Modular symmetry of localized modes
Tatsuo Kobayashi, Hajime Otsuka, Shohei Takada, Hikaru Uchida
Physical Review D, 110, 12, 2024年12月15日
研究論文（学術雑誌）, We study the modular symmetry of localized modes on fixed points of T2/Z2 orbifold. First, we find that the localized modes with even (odd) modular weight generally have Δ(6n2) [Δ′(6n2)] modular flavor symmetry. Moreover, when we consider an additional Ansatz, the localized modes with even (odd) modular weight generally enjoy S3 (S4′) modular flavor symmetry, and we show the concrete wave functions of the localized modes.

Non-invertible flavor symmetries in magnetized extra dimensions
Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2024, 11, 2024年11月
研究論文（学術雑誌）, We discuss non-invertible symmetries in toroidal compactifications of higher dimensional Yang-Mills theory with magnetic fluxes, which can be regarded as an effective action of type IIB string theory with magnetized D-branes. Specifically, we derive fusion rules of discrete isometry operators, which are invariant under the ℤN orbifold twist. It turns out that degenerate chiral zero-modes non-trivially transform under the non-invertible symmetries in the context of quantum mechanics. Hence, non-invertible symmetries correspond to flavor symmetries of chiral zero modes and determine their flavor structure. We explicitly show the representations and selection rules of chiral zero modes on their wave functions. These zero modes may correspond to generations of quarks and leptons in four-dimensional low-energy effective field theory.

Spontaneous CP violation and partially broken modular flavor symmetries
Tetsutaro Higaki, Tatsuo Kobayashi, Kaito Nasu, Hajime Otsuka
Journal of High Energy Physics, 2024, 9, 2024年09月
研究論文（学術雑誌）, We study the realization of spontaneous CP violation through moduli stabilization. In modular flavor models, the source of CP violation is the vacuum expectation values of the complex structure moduli of toroidal compact space. We demonstrate that the combined effects of Type IIB flux compactifications with modular invariant couplings between the moduli and matter fields can induce spontaneous CP violation without or with supersymmetry breaking. Furthermore, some general properties of CP and modular invariant scalar potentials are presented. It is found that certain modifications or partial breakings of modular symmetry are useful in generating spontaneous CP violation.

Modular forms and hierarchical Yukawa couplings in heterotic Calabi-Yau compactifications
Keiya Ishiguro, Tatsuo Kobayashi, Satsuki Nishimura, Hajime Otsuka
Journal of High Energy Physics, 2024, 8, 2024年08月
研究論文（学術雑誌）, We study the modular symmetry in heterotic string theory on Calabi-Yau threefolds. In particular, we examine whether moduli-dependent holomorphic Yukawa couplings are described by modular forms in the context of heterotic string theory with standard embedding. We find that SL(2, ℤ) modular symmetry emerges in asymptotic regions of the Calabi-Yau moduli space. The instanton-corrected holomorphic Yukawa couplings are then given by modular forms under SL(2, ℤ) or its congruence subgroups such as Γ0(3) and Γ0(4). In addition to the modular symmetry, it turns out that another coupling selection rule controls the structure of holomorphic Yukawa couplings. Furthermore, the coexistence of both the positive and negative modular weights for matter fields leads to a hierarchical structure of matter field Kähler metric. Thus, these holomorphic modular forms and the matter field Kähler metric play an important role in realizing a hierarchical structure of physical Yukawa couplings.

Flux Landscape with enhanced symmetry not on SL(2, ℤ) elliptic points
Keiya Ishiguro, Takafumi Kai, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2024, 2, 2024年02月
研究論文（学術雑誌）, We study structures of solutions for SUSY Minkowski F-term equations on two toroidal orientifolds with h2,1 = 1. Following our previous study [1], with fixed upper bounds of a flux D3-brane charge Nflux, we obtain a whole Landscape and a distribution of degeneracies of physically-distinct solutions for each case. In contrast to our previous study, we consider a non-factorizable toroidal orientifold and its Landscape on which SL(2, ℤ) is violated into a certain congruence subgroup, as it had been known in past studies. We find that it is not the entire duality group that a complex-structure modulus U enjoys but its outer semi-direct product with a “scaling” outer automorphism group. The fundamental region is enlarged to include the |U| < 1 region. In addition, we find that high degeneracy is observed at an elliptic point, not of SL(2, Z) but of the outer automorphism group. Furthermore, ℤ2-enhanced symmetry is realized on the elliptic point. The outer automorphism group is exceptional in the sense that it is consistent with a symplectic basis transformation of background three-cycles, as opposed to the outer automorphism group of SL(2, ℤ). We also compare this result with Landscape of another factorizable toroidal orientifold.

Modular flavor models with positive modular weights: a new lepton model building
Tatsuo Kobayashi, Takaaki Nomura, Hiroshi Okada, Hajime Otsuka
Journal of High Energy Physics, 2024, 1, 2024年01月
研究論文（学術雑誌）, We propose an interesting assignment of positive modular weights for fields in a modular non-Abelian discrete flavor symmetry. By this assignment, we can construct inverse seesaw and linear seesaw models without any additional symmetries which possess good testability in current experiments. At first, we discuss possibilities for positive modular weights from a theoretical point of view. Then we show concrete examples of inverse seesaw and linear seesaw scenarios applying modular A 4 symmetry as examples and demonstrate some predictions as well as consistency with experimental results such as neutrino masses and mixings.

Radiative correction on moduli stabilization in modular flavor symmetric models
Tatsuo Kobayashi, Kaito Nasu, Riku Sakuma, Yusuke Yamada
Physical Review D, 108, 11, American Physical Society (APS), 2023年12月29日
研究論文（学術雑誌）

Moduli inflation from modular flavor symmetries
Yoshihiko Abe, Tetsutaro Higaki, Fumiya Kaneko, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2023, 6, 2023年07月
研究論文（学術雑誌）, We study slow-roll inflation model controlled by the modular flavor symmetry. In the model, the modulus field plays a role of inflaton and the introduction of the stabilizer field coupled to a modular form in the superpotential produces the inflaton potential. In order to generate the flat direction for the slow-roll inflation, we consider the Kähler potential corrected by the modular form. It is noted that the modulus field perpendicular to the inflaton direction is stabilized during the inflation. The model turns out to be consistent with the current observations and behaves similarly to the α-attractor models in some parameter spaces. The inflaton rolls down to the CP-symmetric vacuum at the end of inflation.

Moduli inflation from modular flavor symmetries
Yoshihiko Abe, Tetsutaro Higaki, Fumiya Kaneko, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2023, 6, Springer Science and Business Media LLC, 2023年06月27日
研究論文（学術雑誌）, Abstract

We study slow-roll inflation model controlled by the modular flavor symmetry. In the model, the modulus field plays a role of inflaton and the introduction of the stabilizer field coupled to a modular form in the superpotential produces the inflaton potential. In order to generate the flat direction for the slow-roll inflation, we consider the Kähler potential corrected by the modular form. It is noted that the modulus field perpendicular to the inflaton direction is stabilized during the inflation. The model turns out to be consistent with the current observations and behaves similarly to the α-attractor models in some parameter spaces. The inflaton rolls down to the CP-symmetric vacuum at the end of inflation.

Moduli inflation from modular flavor symmetries
Yoshihiko Abe, Tetsutaro Higaki, Fumiya Kaneko, Tatsuo Kobayashi, Hajime Otsuka
JOURNAL OF HIGH ENERGY PHYSICS, 6, SPRINGER, 2023年06月
英語, 研究論文（学術雑誌）, We study slow-roll inflation model controlled by the modular flavor symmetry. In the model, the modulus field plays a role of inflaton and the introduction of the stabilizer field coupled to a modular form in the superpotential produces the inflaton potential. In order to generate the flat direction for the slow-roll inflation, we consider the Kahler potential corrected by the modular form. It is noted that the modulus field perpendicular to the inflaton direction is stabilized during the inflation. The model turns out to be consistent with the current observations and behaves similarly to the & alpha;-attractor models in some parameter spaces. The inflaton rolls down to the CP-symmetric vacuum at the end of inflation.

Index theorem on magnetized blow-up manifold of T2=7LN
Tatsuo Kobayashi, Hajime Otsuka, Makoto Sakamoto, Maki Takeuchi, Yoshiyuki Tatsuta, Hikaru Uchida
PHYSICAL REVIEW D, 107, 7, AMER PHYSICAL SOC, 2023年04月
英語, 研究論文（学術雑誌）, We investigate blow-up manifolds of T2=7LN(N = 2; 3; 4; 6) orbifolds with magnetic flux. First, we construct the blow-up manifolds and zero-mode wave functions on them more precisely. In particular, through an appropriate singular gauge transformation, winding numbers of wave functions on T2=7LN can be replaced with localized curvature and localized flux at orbifold fixed points. In addition, since the blow-up manifolds have no singularities, we apply the Atiyah-Singer index theorem to them; the chiral zero-mode number is given by the total magnetic flux. It can be also applied for T2=7LN orbifolds through the blow-up process, and then we find that it is consistent with the zero-mode counting formula in M. Sakamoto et al. [Zero-mode counting formula and zeros in orbifold compactifications, Phys. Rev. D 102, 025008 (2020).]. Furthermore, the Atiyah-Singer index theorem shows that an additional degree of freedom of localized flux gives new chiral zero modes. We study their wave functions and then we find that they correspond to localized modes at the orbifold singular points. We also calculate their Yukawa couplings.

Generalized matter parities from finite modular symmetries
Tatsuo Kobayashi, Satsuki Nishimura, Hajime Otsuka, Morimitsu Tanimoto, Kei Yamamoto
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, 2023, 4, OXFORD UNIV PRESS INC, 2023年04月
英語, 研究論文（学術雑誌）, We classify a supersymmetric extension of the Standard Model by discrete symmetries originating from finite modular symmetries Gamma(N). Since all the couplings in supersymmetric theories of finite modular symmetries Gamma(N) are described by holomorphic modular forms with even modular weights, renormalizable and non-renormalizable operators such as baryon- and/or lepton-number violating operators are severely constrained. From the modular transformation of matter multiplets with modular weight 1/M, we find Z(2M) symmetries, including the generalized baryon and lepton parities, R-parity, Z(3) baryon triality and Z(6) proton hexality. Such Z(2M) symmetries are enlarged to Z(2M) (sic) Z(2)(CP) symmetries together with the CP transformation.

4D modular flavor symmetric models inspired by a higher-dimensional theory
Shota Kikuchi, Tatsuo Kobayashi, Hajime Otsuka, Morimitsu Tanimoto, Hikaru Uchida, Kei Yamamoto
Physical Review D, 2022年08月01日
研究論文（学術雑誌）, We study a scenario to derive four-dimensional modular flavor symmetric
models from higher dimensional theory by assuming the compactification
consistent with the modular symmetry. In our scenario, wavefunctions in extra
dimensional compact space are modular forms. That leads to constraints on
combinations between modular weights and $\Gamma_N$ ($\Gamma_N')$
representations of matter fields. We also present illustrating examples.

Lepton flavor violation, lepton (g − 2)μ, e and electron EDM in the modular symmetry
Tatsuo Kobayashi, Hajime Otsuka, Morimitsu Tanimoto, Kei Yamamoto
Journal of High Energy Physics, 2022年08月
研究論文（学術雑誌）, We study the lepton flavor violation (LFV), the leptonic magnetic moments
$(g-2)_{\mu,\,e} $ and the electric dipole moment (EDM) of the electron in the
Standard-Model Effective Field Theory with the $\Gamma_N$ modular flavor
symmetry. We employ the stringy Ansatz on coupling structure that 4-point
couplings of matter fields are written by a product of 3-point couplings of
matter fields. We take the level 3 finite modular group, $\Gamma_3$ for the
flavor symmetry, and discuss the dipole operators at nearby fixed point
$\tau=i$, where observed lepton masses and mixing angles are well reproduced.
Suppose the anomaly of the anomalous magnetic moment of the muon to be evidence
of the new physics (NP), we have related it with $(g-2)_{e}$, LFV decays, and
the electron EDM. It is found that the NP contribution to $(g-2)_{e}$ is
proportional to the lepton masses squared likewise the naive scaling. We also
discuss the correlations among the LFV processes $\mu\to e\gamma$, $\tau\to
\mu\gamma$ and $\tau\to e\gamma$, which are testable in the future. The
electron EDM requires the tiny imaginary part of the relevant Wilson
coefficient in the basis of real positive charged lepton masses, which is
related to the $\mu\to e\gamma$ transition in our framework.

Modular symmetry in the SMEFT
Tatsuo Kobayashi, Hajime Otsuka, Morimitsu Tanimoto, Kei Yamamoto
Physical Review D, 105, 5, 2022年03月01日
研究論文（学術雑誌）, We study the modular symmetric standard model effective field theory. We employ the stringy Ansatz on coupling structure that 4-point couplings y(4) of matter fields are written by a product of 3-point couplings y(3) of matter fields, i.e., y(4)=y(3)y(3). In this framework, we discuss the flavor structure of bilinear fermion operators and 4-fermion operators, where the holomorphic and antiholomorphic modular forms appear. From the Ansatz, the A4 modular-invariant semileptonic four-fermion operator [ĒRΓER][D¯RΓDR] does not lead to the flavor changing (FC) processes since this operator would be constructed in terms of gauge couplings g as y(3)∼g. The chirality flipped bilinear operator [D¯RΓDL] also does not lead FC if the mediated mode corresponds to the Higgs boson Hd. In this case, the flavor structure of this operator is the exactly same as the mass matrix. On the other hand, if the flavor structure of the operator is not the exactly same as the mass matrix, the situation would change drastically. Then, we obtain the nontrivial relations of FC transitions at nearby fixed points τ=i,ω,i∞, which are testable in the future. As an application, we discuss the relations of the lepton flavor violation processes μ→eγ,τ→μγ and τ→eγ at nearby τe=i, where the successful lepton mass matrix was obtained. We also study the flavor changing 4-quark operators in the A4 modular symmetry of quarks. As a result, the minimal flavor violation could be realized by taking relevant specific parameter sets of order one.

Symplectic modular symmetry in heterotic string vacua: flavor, CP, and R-symmetries
Keiya Ishiguro, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2022, 1, 2022年01月
研究論文（学術雑誌）, We examine a common origin of four-dimensional flavor, CP, and U(1)R symmetries in the context of heterotic string theory with standard embedding. We find that flavor and U(1)R symmetries are unified into the Sp(2h + 2, ℂ) modular symmetries of Calabi-Yau threefolds with h being the number of moduli fields. Together with the ℤ2CP CP symmetry, they are enhanced to GSp(2h + 2, ℂ) ≃ Sp(2h + 2, ℂ) ⋊ ℤ2CP generalized symplectic modular symmetry. We exemplify the S3, S4, T′, S9 non-Abelian flavor symmetries on explicit toroidal orbifolds with and without resolutions and ℤ2, S4 flavor symmetries on three-parameter examples of Calabi-Yau threefolds. Thus, non-trivial flavor symmetries appear in not only the exact orbifold limit but also a certain class of Calabi-Yau three-folds. These flavor symmetries are further enlarged to non-Abelian discrete groups by the CP symmetry.

Spontaneous CP violation and symplectic modular symmetry in Calabi-Yau compactifications
Keiya Ishiguro, Tatsuo Kobayashi, Hajime Otsuka
Nuclear Physics B, 973, 2021年12月
研究論文（学術雑誌）, We explore the geometrical origin of CP and the spontaneous CP violation in Calabi-Yau compactifications. We find that the CP symmetry is identified with an outer automorphism of the symplectic modular group in the large complex structure regime of Calabi-Yau threefolds, thereby enlarging the symplectic modular group to their semidirect product group. The spontaneous CP violation is realized by the introduction of fluxes, whose effective action is invariant under CP as well as the discrete Z2 symmetry or Z4 R-symmetry. We explicitly demonstrate the spontaneous CP violation on a specific Calabi-Yau threefold.

Hierarchical structure of physical Yukawa couplings from matter field Kähler metric
Keiya Ishiguro, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2021, 7, 2021年07月
研究論文（学術雑誌）, We study the impacts of matter field Kähler metric on physical Yukawa couplings in string compactifications. Since the Kähler metric is non-trivial in general, the kinetic mixing of matter fields opens a new avenue for realizing a hierarchical structure of physical Yukawa couplings, even when holomorphic Yukawa couplings have the trivial structure. The hierarchical Yukawa couplings are demonstrated by couplings of pure untwisted modes on toroidal orbifolds and their resolutions in the context of heterotic string theory with standard embedding. Also, we study the hierarchical couplings among untwisted and twisted modes on resolved orbifolds.

Landscape of modular symmetric flavor models
Keiya Ishiguro, Tatsuo Kobayashi, Hajime Otsuka
Journal of High Energy Physics, 2021, 3, 2021年03月
研究論文（学術雑誌）, We study the moduli stabilization from the viewpoint of modular flavor symmetries. We systematically analyze stabilized moduli values in possible configurations of flux compactifications, investigating probabilities of moduli values and showing which moduli values are favorable from our moduli stabilization. Then, we examine their implications on modular symmetric flavor models. It is found that distributions of complex structure modulus τ determining the flavor structure are clustered at a fixed point with the residual ℤ3 symmetry in the SL(2, ℤ) fundamental region. Also, they are clustered at other specific points such as intersecting points between |τ|2 = k/2 and Re τ = 0,±1/4,±1/2, although their probabilities are less than the ℤ3 fixed point. In general, CP-breaking vacua in the complex structure modulus are statistically disfavored in the string landscape. Among CP-breaking vacua, the values Re τ = ±1/4 are most favorable in particular when the axio-dilaton S is stabilized at Re S = ±1/4. That shows a strong correlation between CP phases originated from string moduli.

Modular symmetry by orbifolding magnetized T ² × T ²: realization of double cover of Γ N
Shota Kikuchi, Tatsuo Kobayashi, Hajime Otsuka, Shintaro Takada, Hikaru Uchida
Journal of High Energy Physics, 2020, 11, 2020年11月
研究論文（学術雑誌）, We study the modular symmetry of zero-modes on T12×T22 and orbifold compactifications with magnetic fluxes, M1, M2, where modulus parameters are identified. This identification breaks the modular symmetry of T12×T22, SL(2, ℤ)1× SL(2, ℤ)2 to SL(2, ℤ) ≡ Γ. Each of the wavefunctions on T12×T22 and orbifolds behaves as the modular forms of weight 1 for the principal congruence subgroup Γ(N), N being 2 times the least common multiple of M1 and M2. Then, zero-modes transform each other under the modular symmetry as multiplets of double covering groups of ΓN such as the double cover of S4.

Common origin of the strong CP and CKM phases in string compactifications
Tatsuo Kobayashi, Hajime Otsuka
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 807, 2020年08月10日
研究論文（学術雑誌）, We explore the scenario where both the strong CP and Cabbibo-Kobayashi-Maskawa (CKM) phases are determined by the same axion field. Such a scenario is naturally realized in string compactifications. We find that there exists parameter region to realize the tiny strong CP phase and observed CKM phase in magnetized D-brane models.

Loop Fayet-Iliopoulos terms in T2/Z2 models: Instability and moduli stabilization
Hiroyuki Abe, Tatsuo Kobayashi, Shohei Uemura, Junji Yamamoto
Physical Review D, 102, 4, American Physical Society (APS), 2020年08月05日
研究論文（学術雑誌）

Challenge for spontaneous CP violation in Type IIB orientifolds with fluxes
Tatsuo Kobayashi, Hajime Otsuka
Physical Review D, 102, 2, 2020年07月15日
研究論文（学術雑誌）, We systematically investigate the possibilities of realizing the spontaneous CP violation in Type IIB flux compactifications on toroidal orientifolds. Our detailed analysis for a generic choice of three-form fluxes leads to the presence of flat directions, where CP-breaking and -conserving vacua are degenerate, indicating that flux compactifications are not sufficient to realize the spontaneous CP violation. Furthermore, the four-dimensional CP can be embedded into the duality symmetries, namely modular symmetries for a particular choice of fluxes.

Classification of discrete modular symmetries in type IIB flux vacua
Tatsuo Kobayashi, Hajime Otsuka
Physical Review D, 101, 10, 2020年05月15日
研究論文（学術雑誌）, We classify discrete modular symmetries in the effective action of Type IIB string on toroidal orientifolds with three-form fluxes, emphasizing on T6/Z2 and T6/(Z2×Z2′) orientifold backgrounds. In the three-form flux background, the modular group is spontaneously broken down to its congruence subgroup whose pattern is severely constrained by a quantization of fluxes and tadpole cancellation conditions. We explicitly demonstrate that the congruence subgroups appearing in the effective action arise on magnetized D-branes wrapping certain cycles of tori.

Flavor structure of magnetized T ² /ℤ2 blow-up models
Tatsuo Kobayashi, Hajime Otsuka, Hikaru Uchida
Journal of High Energy Physics, 2020, 3, 2020年03月01日
研究論文（学術雑誌）, We discuss the flavor structure in resolution of magnetized T2/ℤ2 orbifold models. The flavor structure of Yukawa couplings among chiral zero-modes is sensitive to radii of the resolved fixed points of T2/ℤ2 orbifold. We show in concrete models that the realistic mass hierarchy and mixing angles of the quark sector can be realized at certain values of blow-up radii, where the number of parameters in the blow-up model can be smaller than toroidal orbifold one.

F-term moduli stabilization and uplifting
Tatsuo Kobayashi, Osamu Seto, Shintaro Takada, Takuya H. Tatsuishi, Shohei Uemura, Junji Yamamoto
Progress of Theoretical and Experimental Physics, 2019, 9, 2019年09月26日
研究論文（学術雑誌）, © 2019 The Author(s). We study Kähler moduli stabilization in type IIB superstring theory. We propose a new moduli stabilization mechanism by the supersymmetry breaking chiral superfield which is coupled to Kähler moduli in the Kähler potential. We also study its uplifting of the Large Volume Scenario (LVS). In both cases, the form of the superpotential is crucial for moduli stabilization. We confirm that our uplifting mechanism does not destabilize the vacuum of the LVS drastically.

Revisiting instabilities of S1/Z2 models with loop-induced Fayet-Iliopoulos terms
Hiroyuki Abe, Tatsuo Kobayashi, Shohei Uemura, Junji Yamamoto
Physical Review D, 100, 6, 065020-1, 065020-10, American Physical Society (APS), 2019年09月, ［査読有り］
英語, 研究論文（学術雑誌）

Wavefunctions and Yukawa couplings on resolutions of T²/ℤN orbifolds
Tatsuo Kobayashi, Hajime Otsuka, Hikaru Uchida
Journal of High Energy Physics, 2019, 8, 2019年08月01日
研究論文（学術雑誌）, We propose matter wavefunctions on resolutions of T2/ℤN singularities with constant magnetic fluxes. In the blow-down limit, the obtained wavefunctions of chiral zero-modes result in those on the magnetized T2/ℤN orbifold models, but the wavefunctions of ℤN -invariant zero-modes receive the blow-up effects around fixed points of T2/ℤN orbifolds. Such blow-up effects change the selection rules and Yukawa couplings among the chiral zero-modes as well as the modular symmetry, in contrast to those on the magnetized T2/ℤN orbifold models.

Zero-mode product expansions and higher order couplings in gauge backgrounds
Masaki Honda, Tatsuo Kobayashi, Hajime Otsuka
PHYSICAL REVIEW D, 100, 2, AMER PHYSICAL SOC, 2018年12月08日
英語, 研究論文（学術雑誌）, We study a four-dimensional low-energy effective field theory derived from
extra dimensional field theories with general gauge backgrounds. We find that
products among fermionic zero-modes and lightest scalar modes are expanded by
other fermionic zero-modes and lightest scalar modes. Using this aspect, we
show that higher-order couplings among the fermionic zero-modes and the
lightest scalar mode can be decomposed into three-point couplings. This
selection rule originating from a structure of the Dirac-type operators
indicates the operator product expansion the underlying conformal field theory.

Quark mass matrices in magnetized orbifold models with localized Fayet-Iliopoulos terms
Hiroyuki Abe, Tatsuo Kobayashi, Shintaro Takada, Shio Tamba, Takuya H. Tatsuishi
Physical Review D, 98, 106017, 106017-1, 106017-8, 2018年11月, ［査読有り］
英語, 研究論文（学術雑誌）

20pAL-5 オービフォールド上の複数のDブレーンインスタントンが生成するモジュライポテンシャル
上村 尚平, 小林 達夫
日本物理学会講演概要集, 71, 40, 40, 一般社団法人日本物理学会, 2016年
日本語

II型超弦理論における軽いモジュライ場とグラビティーノ問題
秋田 謙介, 小林 達夫, 及川 茜, 大塚 啓
日本物理学会講演概要集, 71, 32, 32, 一般社団法人 日本物理学会, 2016年
日本語,

私たちは超弦理論の有効理論に基づき、グラビティーノ問題についての研究を行った。 まず、II型超弦理論の枠組みで超対称性を破らない軽いモジュライ場が存在するモデルの構築が可能なことを示す。 IIB型超弦理論では、軽い複素構造モジュライ場が存在する。初期宇宙において、軽い複素構造モジュライ場の崩壊によって、エントロピーが多く生成され、グラビティーノの量が薄まるため、グラビティーノ問題が回避されることを説明する。上記の内容は、arXiv1603.08399[hep-ph]に基づく。

Dilution of axion dark radiation by thermal inflation
Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto
Physical Review D - Particles, Fields, Gravitation and Cosmology, 92, 2, American Physical Society, 2015年07月13日, ［査読有り］
英語, 研究論文（学術雑誌）, Axions in the Peccei-Quinn (PQ) mechanism provide a promising solution to the strong CP problem in the standard model of particle physics. Coherently generated PQ scalar fields could dominate the energy density in the early Universe and decay into relativistic axions, which would conflict with the current dark radiation constraints. We study the possibility that a thermal inflation driven by a U(1) gauged Higgs field dilutes such axions. A well-motivated extra gauged U(1) would be the local B-L symmetry. We also discuss the implication for the case of U(1)B-L and an available baryogenesis mechanism in such cosmology.

D-brane instanton induced μ terms and their hierarchical structure
Hiroyuki Abe, Tatsuo Kobayashi, Yoshiyuki Tatsuta, Shohei Uemura
Physical Review D - Particles, Fields, Gravitation and Cosmology, 92, 2, American Physical Society, 2015年07月06日, ［査読有り］
英語, 研究論文（学術雑誌）, We study the μ-term matrix of Higgs pairs induced by the D-brane instanton effects in intersecting D6-brane models compactified on T6. It is found that the μ-term matrix has a certain permutation symmetry and its eigenvalues have large hierarchical structure without fine-tuning.

Dilution of axion dark radiation
Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto
Proceedings of Science, 22-29-July-2015, 2015年
研究論文（国際会議プロシーディングス）, The Peccei-Quinn (PQ) mechanism provide a promising solution to the strong CP problem in the standard model of particle physics. Axion appears as its pseudo-Nambu-Goldstone boson of the PQ symetry breaking. Coherently generated PQ scalar fields could dominate the energy density in the early Universe and decay into relativistic axions, which would conflict with the current dark radiation constraints. We show that a thermal inflation driven by a U(1) gauged Higgs field dilutes such axions. We discuss an available baryogenesis mechanism for the U(1)B-L gauge symmetry.

Axion Dark Radiation and its Dilution
Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto
Proceedings of the 11th Patras Workshop on Axions, WIMPs and WISPs, PATRAS 2015, 228, 231, 2015年
研究論文（国際会議プロシーディングス）, Axions in the Peccei-Quinn (PQ) mechanism provide a promising solution to the strong CP problem in the standard model of particle physics. Coherently generated PQ scalar fields could dominate the energy density in the early Universe and decay into relativistic axions, which would conflict with the current dark radiation constraints. We show that a thermal inflation driven by a U(1) gauged Higgs field dilutes such axions. We discuss an available baryogenesis mechanism for the U(1)B-L gauge symmetry.

27pSD-6 複数のDブレーンインスタントンによる非摂動効果の現象論的側面
上村 尚平, 小林 達夫, 龍田 佳幸
日本物理学会講演概要集, 70, 37, 37, 一般社団法人日本物理学会, 2015年
日本語

22aDA-1 Dブレーン模型のμターム
上村 尚平, 安倍 博之, 小林 達夫, 龍田 佳幸
日本物理学会講演概要集, 70, 9, 9, 一般社団法人日本物理学会, 2015年
日本語

Non-Abelian discrete flavor symmetries of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta
JOURNAL OF HIGH ENERGY PHYSICS, 1406, 6, SPRINGER, 2014年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We study discrete flavor symmetries of the models based on a ten-dimensional supersymmetric Yang-Mills (10D SYM) theory compactified on magnetized tori. We assume non-vanishing non-factorizable fluxes as well as the orbifold projections. These setups allow model-building with more various flavor structures. Indeed, we show that there exist various classes of non-Abelian discrete flavor symmetries. In particular, we find that S-3 flavor symmetries can be realized in the framework of the magnetized 10D SYM theory for the first time.

Polynomial inflation models after BICEP2
Tatsuo Kobayashi, Osamu Seto
Physical Review D - Particles, Fields, Gravitation and Cosmology, 89, 10, American Physical Society, 2014年05月21日, ［査読有り］
英語, 研究論文（学術雑誌）, Large field inflation models are favored by the recent BICEP2 that has detected gravitational wave modes generated during inflation. We study general large field inflation models for which the potential contains (constant) quadratic and quartic terms of inflaton field. We show, in this framework, those inflation models can generate the fluctuation with the tensor-to-scalar ratio of 0.2 as well as the scalar spectral index of 0.96
those are very close to the center value of the tensor-to-scalar ratio reported by BICEP2 as well as Planck. Finally, we briefly discuss the particle physics model building of inflation. © 2014 American Physical Society.

Polynomial inflation models after BICEP2
Tatsuo Kobayashi, Osamu Seto
PHYSICAL REVIEW D, 89, 10, AMER PHYSICAL SOC, 2014年05月, ［査読有り］
英語, 研究論文（学術雑誌）, Large field inflation models are favored by the recent BICEP2 that has detected gravitational wave modes generated during inflation. We study general large field inflation models for which the potential contains (constant) quadratic and quartic terms of inflaton field. We show, in this framework, those inflation models can generate the fluctuation with the tensor-to-scalar ratio of 0.2 as well as the scalar spectral index of 0.96; those are very close to the center value of the tensor-to- scalar ratio reported by BICEP2 as well as Planck. Finally, we briefly discuss the particle physics model building of inflation.

Flavor structure in D-brane models: Majorana neutrino masses
Yuta Hamada, Tatsuo Kobayashi, Shohei Uemura
JOURNAL OF HIGH ENERGY PHYSICS, 1405, 5, SPRINGER, 2014年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the flavor structure in intersecting D-brane models. We study anomalies of the discrete flavor symmetries. We analyze the Majorana neutrino masses, which can be generated by D-brane instanton effects. It is found that a certain pattern of mass matrix is obtained and the cyclic permutation symmetry remains unbroken. As a result, trimaximal mixing matrix can be realized if Dirac neutrino mass and charged lepton mass matrices are diagonal.

Flavor landscape of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta
JOURNAL OF HIGH ENERGY PHYSICS, 1404, 4, SPRINGER, 2014年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the flavor landscape of the visible sector of particle physics models based on a ten-dimensional super Yang-Mills theory compactified on magnetized tori preserving four-dimensional Nu = 1 supersymmetry. Recently, we constructed a semirealistic model which contains the minimal supersymmetric standard model (MSSM) using an ansatz of magnetic fluxes and orbifolding projections. However, we can consider more various configurations of magnetic fluxes and orbifolding projections preserving fourdimensional N = 1 supersymmetry. We research systematically such possibilities for leading to MSSM-like models and study their phenomenological aspects.

Discrete R-symmetries and anomaly universality in heterotic orbifolds
Nana G. Cabo Bizet, Tatsuo Kobayashi, Damian K. Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala
JOURNAL OF HIGH ENERGY PHYSICS, 1402, 2, SPRINGER, 2014年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We study discrete R-symmetries, which appear in the 4D low energy effective field theory derived from heterotic orbifold models. We derive the R-symmetries directly from the geometrical symmetries of the orbifolds. In particular, we obtain the corresponding R-charges by requiring that the couplings be invariant under these symmetries. This allows for a more general treatment than the explicit computations of correlation functions made previously by the authors, including models with discrete Wilson lines, and orbifold symmetries beyond plane-by-plane rotational invariance. The R-charges obtained in this manner differ from those derived in earlier explicit computations. We study the anomalies associated with these R-symmetries, and comment on the results.

Instability of colliding metastable strings
Takashi Hiramatsu, Minoru Eto, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi
JOURNAL OF HIGH ENERGY PHYSICS, 1401, 1, SPRINGER, 2014年01月, ［査読有り］
英語, 研究論文（学術雑誌）, The breaking of U(1) R symmetry plays a crucial role in modeling the breaking of supersymmetry (SUSY). In the models that possess both SUSY preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes, whose surfaces are constituted by domain walls interpolating a false and a true vacuum with some winding numbers, can exist. Their (in) stability can strongly constrain SUSY breaking models theirselves. In the present study, we investigate the dynamical (in) stability of two colliding metastable tube-like strings by field-theoretic simulations. From them, we find that the strings become unstable, depending on the relative collision angle and speed of two strings, and the false vacuum is eventually filled out by the true vacuum owing to rapid expansion of the strings or unstable bubbles created as remnants of the collision.

Z (N) twisted orbifold models with magnetic flux
Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto
JOURNAL OF HIGH ENERGY PHYSICS, 1, SPRINGER, 2014年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We propose new backgrounds of extra dimensions to lead to four-dimensional chiral models with three generations of matter fermions, that is T (2) /Z (N) twisted orbifolds with magnetic fluxes. We consider gauge theory on six-dimensional space-time, which contains the T (2) /Z (N) orbifold with magnetic flux, Scherk-Schwarz phases and Wilson line phases. We classify all the possible Scherk-Schwarz and Wilson line phases on T (2) /Z (N) orbifolds with magnetic fluxes. The behavior of zero modes is studied. We derive the number of zero modes for each eigenvalue of the Z (N) twist, showing explicitly examples of wave functions. We also investigate Kaluza-Klein mode functions and mass spectra.

Three-generation asymmetric orbifold models from heterotic string theory
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino
JOURNAL OF HIGH ENERGY PHYSICS, 1, SPRINGER, 2014年01月, ［査読有り］
英語, 研究論文（学術雑誌）, Using Z(3) asymmetric orbifolds in heterotic string theory, we construct N = 1 SUSY three-generation models with the standard model gauge group SU(3)(C) x SU(2)(L) x U(1)(Y) and the left-right symmetric group SU(3)(C) x SU(2)(L) x SU(2)(R) x U(1)(B-L). One of the models possesses a gauge flavor symmetry for the Z(3) twisted matter.

More on cosmological constraints on spontaneous R-symmetry breaking models
Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 1, IOP PUBLISHING LTD, 2014年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the spontaneous R-symmetry breaking model and investigate the cosmological constraints on this model due to the pseudo Nambu-Goldstone boson, R-axion. We consider the R-axion which has relatively heavy mass in order to complement our previous work. In this regime, model parameters, R-axions mass and R-symmetry breaking scale, are constrained by Big Bang Nucleosynthesis and overproduction of the gravitino produced from R-axion decay and thermal plasma. We find that the allowed parameter space is very small for high reheating temperature. For low reheating temperature, the U(1)(R) breaking scale f(a) is constrained as f(a) < 10(12-14) GeV regardless of the value of R-axion mass.

Revisiting discrete dark matter model: θ<inf>13</inf> ≠ 0 and ν <inf>R</inf> dark matter
Yuta Hamada, Tatsuo Kobayashi, Atsushi Ogasahara, Yuji Omura, Fumihiro Takayama, Daiki Yasuhara
Journal of High Energy Physics, 2014, 10, Springer Verlag, 2014年, ［査読有り］
英語, 研究論文（学術雑誌）, Abstract: We revisit the discrete dark matter model with the A<
inf>
4<
/inf>
flavor symmetry originally introduced by M.Hirsch et.al. We show that radiative corrections can lead to non-zero θ<
inf>
13<
/inf>
and the non-zero mass for the lightest neutrino. We find an interesting relation among neutrino mixing parameters and it indicates the sizable deviation of s<
inf>
23<
/inf>
from the maximal angle s<
inf>
23<
/inf>
<
sup>
2<
/sup>
= 1/2 and the degenerate mass spectrum for neutrinos. Also we study the possibilities that the right-handed neutrino is a dark matter candidate. Assuming that the thermal freeze-out explains observed dark matter abundance, TeV-scale right-handed neutrino and flavored scalar bosons are required. In such a case, the flavor symmetry plays an important role for the suppression of lepton flavor violating processes as well as for the stability of dark matter. We show that this scenario is viable within currently existing constraints from collider, low energy experiments and cosmological observations.

CKM matrix and flavor symmetries
Takeshi Araki, Hiroyuki Ishida, Hajime Ishimori, Tatsuo Kobayashi, Atsushi Ogasahara
PHYSICAL REVIEW D, 88, 9, AMER PHYSICAL SOC, 2013年11月, ［査読有り］
英語, 研究論文（学術雑誌）, Following the way proposed recently by Hernandez and Smirnov, we seek possible residual symmetries in the quark sector with a focus on the von Dyck groups. We begin with two extreme cases in which both theta(13) and theta(23) or only theta(13) are set to zero. Then, cases where all the Cabibbo-Kobayashi-Maskawa parameters are allowed to take nonzero values are explored. The Z(7) symmetry is favorable to realize only the Cabibbo angle. On the other hand, larger groups are necessary in order to be consistent with all the mixing parameters. Possibilities of embedding the obtained residual symmetries into the Delta(6N(2)) series are also briefly discussed.

Gauge symmetries in heterotic asymmetric orbifolds
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino
NUCLEAR PHYSICS B, 875, 3, 599, 620, ELSEVIER SCIENCE BV, 2013年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study heterotic asymmetric orbifold models. By utilizing the lattice engineering technique, we classify (22,6)-dimensional Narain lattices with right-moving non-Abelian group factors which can be starting points for Z(3) asymmetric orbifold construction. We also calculate gauge symmetry breaking patterns. (C) 2013 Elsevier B.V. All rights reserved.

R-charge conservation and more in factorizable and non-factorizable orbifolds
Nana G. Cabo Bizet, Tatsuo Kobayashi, Damian K. Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala
JOURNAL OF HIGH ENERGY PHYSICS, 5, SPRINGER, 2013年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider the string theory origin of R-charge conservation laws in heterotic orbifold compactifications, deriving the corresponding string coupling selection rule for factorizable and non-factorizable orbifolds, with prime ordered and non-prime ordered point groups. R-charge conservation arises due to symmetries among the worldsheet instantons that can mediate the couplings. Among our results is a previously missed non-trivial contribution to the conserved R-charges from the gamma-phases in non-prime orbifolds, which weakens the R-charge selection rule. Symmetries among the worldsheet instantons can also lead to additional selection rules for some couplings. We make a similar analysis for Rule 4 or the "torus lattice selection rule". Moreover, we identify a new string selection rule, that we call Rule 6 or the "coset vector selection rule".

Phenomenological aspects of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Akane Oikawa, Keigo Sumita
NUCLEAR PHYSICS B, 870, 1, 30, 54, ELSEVIER SCIENCE BV, 2013年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We present a particle physics model based on a ten-dimensional (10D) super Yang-Mills (SYM) theory compactified on magnetized tori preserving four-dimensional N = 1 supersymmetry. The low-energy spectrum contains the minimal supersymmetric standard model with hierarchical Yukawa couplings caused by a wavefunction localization of the chiral matter fields due to the existence of magnetic fluxes, allowing a semi-realistic pattern of the quark and the lepton masses and mixings. We show supersymmetric flavor structures at low energies induced by a moduli-mediated and an anomaly-mediated supersymmetry breaking. (C) 2013 Elsevier B.V. All rights reserved.

Cosmic R-string in thermal history
Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi
JOURNAL OF HIGH ENERGY PHYSICS, 5, SPRINGER, 2013年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study stabilization of an unstable cosmic string associated with spontaneously broken U(1)(R) symmetry, which otherwise causes a dangerous roll-over process. We demonstrate that in a gauge mediation model, messengers can receive enough corrections from the thermal plasma of the supersymmetric standard model particles to stabilize the unstable modes of the string.

Shifted orbifold models with magnetic flux
Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto
Physical Review D - Particles, Fields, Gravitation and Cosmology, 87, 8, 2013年04月08日, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a mechanism to obtain the generation of matter in the standard model. We start from the analysis of the T2/ZN shifted orbifold with magnetic flux, which imposes a ZN symmetry on torus. We also consider several orbifolds such as (T2×T2)/ZN, (T2×T2×T2)/ (ZN×ZN') and (T2×T2×T2)/(Z N×ZN'×ZN'). On such orbifolds, we study the behavior of fermions in two different means - the operator formalism and the explicit analysis of wave functions. For an interesting result, it is found that the number of zero-mode fermions is related to N of the ZN symmetry. In other words, the generation of matter relates to the type of orbifolds. Moreover, we find that shifted orbifold models are severely restricted from realizing three generations. For example, the three-generation model on the type of M4×(T2×T2)/ZN is unique. One can also construct other types of three-generation orbifold models with rich flavor structure. Those results may bring us a realistic model with desired Yukawa structure. © 2013 American Physical Society.

Cosmological constraints on spontaneous R-symmetry breaking models
Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 4, IOP PUBLISHING LTD, 2013年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study general constraints on spontaneous R-symmetry breaking models coming from the cosmological effects of the pseudo Nambu-Goldstone bosons, R-axions. They are substantially produced in the early Universe and may cause several cosmological problems. We focus on relatively long-lived R-axions and find that in a wide range of parameter space, models are severely constrained. In particular, R-axions with mass less than 1 MeV are generally ruled out for relatively high reheating temperature, T-R > 10 GeV.

Cosmic R-string, R-tube and vacuum instability
Minoru Eto, Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi
JOURNAL OF HIGH ENERGY PHYSICS, 3, SPRINGER, 2013年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We show that a cosmic string associated with spontaneous U(1)(R) symmetry breaking gives a constraint for supersymmetric model building. In some models, the string can be viewed as a tube-like domain wall with a winding number interpolating a false vacuum and a true vacuum. Such string causes inhomogeneous decay of the false vacuum to the true vacuum via rapid expansion of the radius of the tube and hence its formation would be inconsistent with the present Universe. However, we demonstrate that there exist metastable solutions which do not expand rapidly. Furthermore, when the true vacua are degenerate, the structure inside the tube becomes involved. As an example, we show a "bamboo"-like solution, which suggests a possibility observing an information of true vacua from outside of the tube through the shape and the tension of the tube.

TeV scale mirage mediation in NMSSM
Tatsuo Kobayashi, Hiroki Makino, Ken-ichi Okumura, Takashi Shimomura, Tsubasa Takahashi
JOURNAL OF HIGH ENERGY PHYSICS, 1, SPRINGER, 2013年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the next-to-minimal supersymmetric standard model. We consider soft supersymmetry breaking parameters, which are induced by the mirage mediation mechanism of supersymmetry breaking. We concentrate on the mirage mediation, where the so-called mirage scale is the TeV scale. In this scenario, we can realize the up-type Higgs soft mass of O(200) GeV, while other masses such as gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation between the effective mu-term and the down-type Higgs soft mass ameliorates the fine-tuning in the electroweak symmetry breaking even for mu = O(500) GeV. The mixing between the doublet and singlet Higgs bosons is suppressed by (kappa/lambda) tan(-1) beta. Then the lightest doublet Higgs mass naturally reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino are light and their linear combination is the lightest superparticle.

Revisiting coupling selection rules in heterotic orbifold models (vol 5, 008, 2012)
Tatsuo Kobayashi, Susha L. Parameswaran, Saul Ramos-Sanchez, Ivonne Zavala
JOURNAL OF HIGH ENERGY PHYSICS, 12, SPRINGER, 2012年12月, ［査読有り］
英語

Runaway, D term and R-symmetry breaking
Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka
PHYSICAL REVIEW D, 86, 9, AMER PHYSICAL SOC, 2012年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the D-term effect on runaway directions of the F-term scalar potential. A minimal renormalizable model is presented where supersymmetry is broken without any pseudomoduli. The model is applied to the hidden sector of gauge mediation for spontaneously breaking R symmetry and generating nonvanishing gaugino masses at the one-loop order.

Massive Modes in Magnetized Brane Models
Yuta Hamada, Tatsuo Kobayashi
PROGRESS OF THEORETICAL PHYSICS, 128, 5, 903, 923, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2012年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We study higher dimensional models with magnetic fluxes, which can be derived from superstring theory. We study mass spectrum and wavefunctions of massless and massive modes for spinor, scalar and vector fields. We compute the 3-point couplings and higher order couplings among massless modes and massive modes in 4D low-energy effective field theory. These couplings have non-trivial behaviors, because wavefunctions of massless and massive modes are non-trivial.

Superfield description of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita
NUCLEAR PHYSICS B, 863, 1, 1, 18, ELSEVIER SCIENCE BV, 2012年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We present a four-dimensional (4D) N = 1 superfield description of supersymmetric Yang-Mills (SYM) theory in ten-dimensional (10D) spacetime with certain magnetic fluxes in compactified extra dimensions preserving partial N = 1 supersymmetry out of full N = 4. We derive a 41) effective action in N = 1 superspace directly from the 10D superfield action via dimensional reduction, and identify its dependence on dilaton and geometric moduli superfields. A concrete model for three generations of quark and lepton superfields are also shown. Our formulation would be useful for building various phenomenological models based on magnetized SYM theories or D-branes. (C) 2012 Elsevier B.V. All rights reserved.

Constraining the Higgs sector from false vacua in the next-to-minimal supersymmetric standard model
Tatsuo Kobayashi, Takashi Shimomura, Tsubasa Takahashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 86, 1, 2012年07月30日, ［査読有り］
英語, 研究論文（学術雑誌）, We study the mass, the mixing, and the coupling with the Z boson of the lightest Higgs boson in the next-to-minimal supersymmetric standard model with the Z 3 symmetry. The vacuum structure of the Higgs potential is analyzed, and the new false vacua are discussed. The significant parameter region can be excluded by requiring the realistic vacuum to be deeper than false vacua. In numerical analysis, we also require the couplings to be perturbative up to the Grand Unified Theory scale. Our analysis results in constraints on the properties of the lightest Higgs boson. © 2012 American Physical Society.

Constraining the Higgs sector from false vacua in the next-to-minimal supersymmetric standard model
Tatsuo Kobayashi, Takashi Shimomura, Tsubasa Takahashi
PHYSICAL REVIEW D, 86, 1, AMER PHYSICAL SOC, 2012年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the mass, the mixing, and the coupling with the Z boson of the lightest Higgs boson in the next- to-minimal supersymmetric standard model with the Z(3) symmetry. The vacuum structure of the Higgs potential is analyzed, and the new false vacua are discussed. The significant parameter region can be excluded by requiring the realistic vacuum to be deeper than false vacua. In numerical analysis, we also require the couplings to be perturbative up to the Grand Unified Theory scale. Our analysis results in constraints on the properties of the lightest Higgs boson.

Lepton flavor models with discrete values of theta(13)
Hajime Ishimori, Tatsuo Kobayashi
PHYSICAL REVIEW D, 85, 12, AMER PHYSICAL SOC, 2012年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the lepton flavor models with the flavor symmetry (Z(N) x Z(N) x Z(N))xZ(3). Our models lead nonvanishing discrete values of theta(13) as well as (12) and theta(23) depending on N. For certain values, our models realize the tribimaximal mixing angles with theta(13) = 0. For other values, our models provide discrete deviation from the tribimaximal mixing angles.

SN
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 21, 30, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the symmetric group SN, which consists of all possible permutations among N objects. In particular, we study S3 and S4, and show their group-theoretical aspects such as conjugacy classes, characters, representations and tensor products.

QD 2N
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 69, 74, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study generic aspects of QD2N and consider QD16 as a simple example.

T′
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 43, 49, Springer, 2012年
英語, 論文集(書籍)内論文, The group T′ is the double covering group of A4=T. In this chapter, we study this group and show its group-theoretical aspects.

Anomalies
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 185, 204, Springer, 2012年
英語, 論文集(書籍)内論文, In general, symmetries at the tree level can be broken by quantum effects, that is, anomalies. We review anomalies of discrete Abelian and non-Abelian symmetries. Also the anomaly-free conditions are given explicitly for the discrete groups, which are studied in the previous chapters.

Σ(2N2)
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 75, 86, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group Σ(2N2), which is isomorphic to (ZN×ZN)⋊Z2. We explain generic aspects and show simple examples, Σ(18), Σ(32) and Σ(50).

Σ(3N3)
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 109, 121, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group Σ(3N3), which is isomorphic to (ZN×ZN×ZN)⋊Z3. We explain generic aspects and show a simple example, Σ(81).

Non-Abelian Discrete Symmetry in Quark/Lepton Flavor Models
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 205, 227, Springer, 2012年
英語, 論文集(書籍)内論文, Non-Abelian discrete groups have been adopted for the flavor models of the quarks and leptons. In this chapter, we present some typical flavor models based on these discrete symmetries. The examples will illustrate how such models are built. However, before discussing the models themselves, we briefly review the main features of recent experimental data regarding neutrino flavor mixing.

Basics of Finite Groups
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 13, 20, Springer, 2012年
英語, 論文集(書籍)内論文, We explain pedagogically the basics of group theory, in particular finite groups. We show several examples in order to obtain a clear understanding of finite groups.

DN
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 51, 60, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the dihedral group, DN. This is the symmetry group of the regular polygon with N sides. We explain group-theoretical aspects for generic DN, and also show explicitly them for simple examples, D4 and D5.

TN
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 97, 108, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group TN, which is isomorphic to ZN⋊Z3. We explain generic aspects and also show simple examples, T7, T13 and T19.

AN
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 31, 41, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group AN, consisting of all even permutations in SN. This group is refered as the alternating group. In particular, we consider A4 and A5, and show their group-theoretical aspects.

Δ(3N2)
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 87, 95, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group Δ(3N2), which is isomorphic to (ZN×ZN)⋊Z3. We explain generic aspects of Δ(3N2) and show a simple example, Δ(27).

Subgroups and Decompositions of Multiplets
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 147, 183, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study systematically subgroups of the discrete groups, which are studied in the previous chapters. We show explicitly breaking patterns of the discrete groups and docompositions of multiplets.

QN
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 61, 68, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the binary dihedral group, QN. Group-theoretical aspects are explained for generic QN and also illustrated for simple examples, Q4 and Q6.

Δ(6N2)
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
Lecture Notes in Physics, 858, 123, 145, Springer, 2012年
英語, 論文集(書籍)内論文, In this chapter, we study the group Δ(6N2), which is isomorphic to (ZN×ZN)⋊S3. We explain generic aspects of Δ(6N2), and give a simple example, Δ(54).

Erratum: Revisiting coupling selection rules in heterotic orbifold models (Journal of High Energy Physics (2012) 05 (008))
Tatsuo Kobayashi, Susha L. Parameswaran, Saúl Ramos-Sánchez, Ivonne Zavala
Journal of High Energy Physics, 2012, 12, 2012年, ［査読有り］
英語, 研究論文（学術雑誌）

Symmetries and vanishing couplings in string-derived low energy effective field theory
Tatsuo Kobayashi
AIP Conference Proceedings, 1467, 194, 199, 2012年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, We study 4D low-energy effective field theory, derived from heterotic string theory on the orbifolds. In particular, we study Abelian and non-Abelian discrete symmetries and their anomalies. Furthermore, stringy computations also provide with stringy coupling selection rules. © 2012 American Institute of Physics.

Constraints from Unrealistic Vacua in the Next-to-Minimal Supersymmetric Standard Model
Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Osamu Seto, Takashi Shimomura
PROGRESS OF THEORETICAL PHYSICS, 126, 6, 1051, 1076, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2011年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study constraints to avoid deep unrealistic minima in the next-to-minimal supersymmetric standard model. We analyze the scalar potential along directions where all of and one of the three Higgs fields develop their vacuum expectation values, and find unrealistic minima deeper than the electroweak symmetry breaking (EWSB) vacuum. These unrealistic minima threaten the realization of successful EWSB and therefore should be avoided. Necessary conditions for avoiding these minima result in constraints on parameters. We show that a wide and significant region of the parameter space, especially a large A, is ruled out by our constraints.

Towards minimal S-4 lepton flavor model
Hajime Ishimori, Tatsuo Kobayashi
JOURNAL OF HIGH ENERGY PHYSICS, 10, SPRINGER, 2011年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study lepton flavor models with the S-4 flavor symmetry. We construct simple models with smaller numbers of flavon fields and free parameters, such that we have predictions among lepton masses and mixing angles. The model with a S-4 triplet flavon is not realistic, but we can construct realistic models with two triplet flavons, or one triplet and one doublet flavons.

NON-ABELIAN DISCRETE FLAVOR SYMMETRIES ON ORBIFOLDS
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, Manabu Sakai
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 26, 23, 4067, 4082, WORLD SCIENTIFIC PUBL CO PTE LTD, 2011年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study non-Abelian flavor symmetries on orbifolds, S-1/Z(2) and T-2/Z(3). Our extra dimensional models realize D-N, Sigma(2N(2)), Delta(3N(2)) and Delta(6N(2)) including A(4) and S-4. In addition, one can also realize their subgroups such as Q(N), T-7, etc. The S-3 flavor symmetry can be realized on both S-1/Z(2) and T-2/Z(3) orbifolds.

D term and gaugino masses in gauge mediation
Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka
JOURNAL OF HIGH ENERGY PHYSICS, 9, SPRINGER, 2011年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We systematically study supersymmetry breaking with non-vanishing F and D terms. We classify the models into two categories and find that a certain class of models necessarily has runaway behavior of scalar potential, while the other needs the Fayet-Iliopoulos term to break supersymmetry. The latter class is useful to have a simple model of gauge mediation where the vacuum is stable everywhere and the gaugino mass is generated at the one-loop order.

Note on moduli stabilization, supersymmetry breaking, and axiverse
Tetsutaro Higaki, Tatsuo Kobayashi
PHYSICAL REVIEW D, 84, 4, AMER PHYSICAL SOC, 2011年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We study properties of moduli stabilization in the four dimensional N = 1 supergravity theory with heavy moduli and would-be saxion-axion multiplets, including light string-theoretic axions. We give general formulation for the scenario that heavy moduli and saxions are stabilized while axions remain light, assuming that moduli are stabilized near the supersymmetric solution. One can find stable vacuum, i.e. nontachyonic saxions, in the nonsupersymmetric Minkowski vacua. We also discuss the cases where the moduli are coupled to the supersymmetry breaking sector and/or moduli have contributions to supersymmetry breaking. Futhermore, we study the models with axions originating from matterlike fields. Our analysis on moduli stabilization is applicable even if there are not light axion multiplets.

(Extra)ordinary gauge/anomaly mediation
Tatsuo Kobayashi, Yuichiro Nakai, Manabu Sakai
JOURNAL OF HIGH ENERGY PHYSICS, 6, SPRINGER, 2011年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We study anomaly mediation models with gauge mediation effects from messengers which have a general renormalizable mass matrix with a supersymmetry-breaking spurion. Our models lead to a rich structure of supersymmetry breaking terms in the visible sector. We derive sum rules among the soft scalar masses for each generation. Our sum rules for the first and second generations are the same as those in general gauge mediation, but the sum rule for the third generation is different because of the top Yukawa coupling. We find the parameter space where the tachyonic slepton problem is solved. We also explore the case in which gauge mediation causes the anomalously small gaugino masses. Since anomaly mediation effects on the gaugino masses exist, we can obtain viable mass spectrum of the visible sector fields.

Towards the MSSM from F-theory
Kang-Sin Choi, Tatsuo Kobayashi
PHYSICS LETTERS B, 693, 3, 330, 333, ELSEVIER SCIENCE BV, 2010年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the MSSM in F-theory. Its group is the commutant to a structure group SU(5) x U(1)gamma of a gauge bundle in E(8). The spectrum contains three generations of quarks and leptons plus vectorlike electroweak and colored Higgses. The minimal MSSM Yukawa couplings with matter parity is obtained at the renormalizable level. (c) 2010 Elsevier B.V. All rights reserved.

Constraints from unrealistic vacua in the supersymmetric standard model with neutrino mass operators
Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Takashi Shimomura
PHYSICAL REVIEW D, 82, 7, AMER PHYSICAL SOC, 2010年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We analyze a scalar potential of the minimal supersymmetric standard model (MSSM) with neutrino mass operators along unbounded-from-below and color and/or charged breaking directions. We show necessary conditions to avoid the potential minima which can be deeper than the realistic vacuum. These conditions would constrain more strongly than conditions in the MSSM without taking into account neutrino mass operators and can improve the predictive power of supersymmetric models with neutrino mass operators.

Revisiting superparticle spectra in superconformal flavor models
Tatsuo Kobayashi, Yuichiro Nakai, Ryo Takahashi
JOURNAL OF HIGH ENERGY PHYSICS, 9, SPRINGER, 2010年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study superparticle spectra in the superconformal flavor scenario with non-universal gaugino masses. The non-universality of gaugino masses can lead to the wino-like or higgsino-like neutralino LSP. Furthermore, it is shown that the parameter space for the higgsino-like LSP includes the region where the fine-tuning problem can be improved. The degeneracy of soft scalar masses does not drastically change when ratios of gaugino masses are of O(1). The degeneracy of scalar masses for squarks and left-handed sleptons would be good enough to avoid the FCNC problem but that of right-handed slepton masses is weak. However, the overall size of right-handed slepton masses becomes larger when the bino becomes heavier. Thus, that would be favorable to avoid the FCNC problem due to soft scalar masses and A-terms.

Constraints from color and/or charge breaking minima in the supersymmetric standard model with right-handed neutrinos
Tatsuo Kobayashi, Takashi Shimomura
PHYSICAL REVIEW D, 82, 3, AMER PHYSICAL SOC, 2010年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider a model where right-handed neutrinos and sneutrinos are introduced to the minimal supersymmetric standard model. In the scalar potential of this model, there exist trilinear and quartic terms in scalar potential that are proportional to Yukawa couplings of neutrinos. Because of these trilinear and quartic terms, color and/or charge breaking (CCB) and unbounded-from-below (UFB) directions appear along which sneutrinos have a vacuum expectation value, making the vacuum of the electroweak symmetry breaking unstable. We analyze the scalar potential of this model and derive necessary conditions for color and/or charge breaking and unbounded-from-below directions to vanish.

Flavor structure from magnetic fluxes and non-Abelian Wilson lines
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
PHYSICAL REVIEW D, 81, 12, AMER PHYSICAL SOC, 2010年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the flavor structure of four-dimensional (4D) effective theories, which are derived from extra dimensional theories with magnetic fluxes and non-Abelian Wilson lines. We study zero-mode wave functions in generic case and compute Yukawa couplings as well as four-point couplings. In our models, we also discuss non-Abelian discrete flavor symmetries such as D-4, Delta(27), and Delta(54). The orbifold background is also studied.

Three-generation models from E-8 magnetized extra dimensional theory
Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Hiroshi Ohki, Manabu Sakai
JOURNAL OF HIGH ENERGY PHYSICS, 5, SPRINGER, 2010年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study 10D super Yang-Mills E-8 theory on the 6D torus compactification with magnetic fluxes. We study systematically the possibilities for realizing 4D supersymmetric standard models with three generations of quarks and leptons. We also study quark mass matrices.

E (6,7,8) magnetized extra-dimensional models
Kang-Sin Choi, Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Yuichiro Nakai, Hiroshi Ohki, Manabu Sakai
EUROPEAN PHYSICAL JOURNAL C, 67, 1-2, 273, 282, SPRINGER, 2010年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study 10D super Yang-Mills theory with the gauge groups E (6), E (7) and E (8). We consider the torus/orbifold compactification with magnetic fluxes and Wilson lines. They lead to 4D interesting models with three families of quarks and leptons, whose profiles in extra dimensions are quasi-localized because of magnetic fluxes.

Non-Abelian Discrete Symmetries in Particle Physics
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yusuke Shimizu, Hiroshi Okada, Morimitsu Tanimoto
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 183, 1, 163, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2010年, ［査読有り］
英語, 研究論文（学術雑誌）, We review pedagogically non-Abelian discrete groups, which play an important role in particle physics. We show group-theoretical aspects for many concrete groups, such as representations and their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discuss them explicitly for S-N, A(N), T', D-N, Q(N), E(2N(2)), Delta(3N(2)), T-7, Sigma(3N(3)), and Delta(6N(2)), which have been applied for model building in particle physics. We also present typical flavor models by using A(4), S-4, and Delta(54) groups. Breaking patterns of discrete groups and decompositions of multiplets are important for applications of the non-Abelian discrete symmetry. We discuss these breaking patterns of the non-Abelian discrete group, which are a powerful tool for model buildings. We also review briefly anomalies of non-Abelian discrete symmetries by using the path integral approach.

Constraints from Color and/or Charge Breaking Minima in the #23;nu SSM
2010年, ［査読有り］

Magnetic flux, Wilson line, and orbifold
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
Physical Review D - Particles, Fields, Gravitation and Cosmology, 80, 12, 2009年12月15日, ［査読有り］
英語, 研究論文（学術雑誌）, We study torus/orbifold models with magnetic flux and Wilson line backgrounds. The number of zero modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology. © 2009 The American Physical Society.

Magnetic flux, Wilson line, and orbifold
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
PHYSICAL REVIEW D, 80, 12, AMER PHYSICAL SOC, 2009年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study torus/orbifold models with magnetic flux and Wilson line backgrounds. The number of zero modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology.

Delta(54) flavor model for leptons and sleptons
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
JOURNAL OF HIGH ENERGY PHYSICS, 12, SPRINGER, 2009年12月, ［査読有り］
英語, We study a Delta(54) x Z(2) flavor model for leptons and sleptons. The tri-bimaximal mixing can be reproduced for arbitrary neutrino masses if certain vacuum alignments of scalar fields are realized. The deviation from the tri-bimaximal mixing of leptons is predicted. The predicted upper bound for sin theta(13) is 0.07. The value of sin theta(23) could be deviated from the maximal mixing considerably while sin theta(12) is hardly deviated from 1/root 3. We also study SUSY breaking terms in the slepton sector. Three families of left-handed and right-handed slepton masses are almost degenerate. Our model leads to smaller values of flavor changing neutral currents than the present experimental bounds.

Non-Abelian discrete flavor symmetries from magnetized/intersecting brane models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
NUCLEAR PHYSICS B, 820, 1-2, 317, 333, ELSEVIER SCIENCE BV, 2009年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study non-Abelian discrete flavor symmetries, which appear in magnetized brane models. For example, D-4, Delta(27) and Delta(54) flavor symmetries can appear with matter fields in several representations. We also study the orbifold background, where non-Abelian flavor symmetries are broken in a certain way. (C) 2009 Published by Elsevier B.V.

Three generation magnetized orbifold models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
NUCLEAR PHYSICS B, 814, 1-2, 265, 292, ELSEVIER SCIENCE BV, 2009年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N = 1 super-Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown. (C) 2009 Elsevier B.V. All rights reserved.

Higher order couplings in magnetized brane models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki
JOURNAL OF HIGH ENERGY PHYSICS, 6, SPRINGER, 2009年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We compute three-point and higher order couplings in magnetized brane models. We show that higher order couplings are written as products of three-point couplings. This behavior is the same as higher order amplitudes by conformal field theory calculations e. g. in intersecting D-brane models.

Lepton flavor model from Delta(54) symmetry
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto
JOURNAL OF HIGH ENERGY PHYSICS, 4, SPRINGER, 2009年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We present the lepton flavor model with Delta(54), which appears typically in heterotic string models on the T-2/Z(3) orbifold. Our model reproduces the tri-bimaximal mixing in the parameter region around degenerate neutrino masses or two massless neutrinos. We predict the deviation from the tri-bimaximal mixing by putting the experimental data of neutrino masses in the normal hierarchy of neutrino masses. The upper bound of sin(2)theta(13) is 0.01. There is the strong correlation between theta(23) and theta(13). Unless theta(23) is deviated from the maximal mixing considerably, theta(13) remains to be tiny.

Duality cascade of softly broken supersymmetric theories
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Kazutoshi Ohta, Yuji Omura, Haruhiko Terao
Physical Review D - Particles, Fields, Gravitation and Cosmology, 79, 4, 2009年02月02日, ［査読有り］
英語, 研究論文（学術雑誌）, We study the duality cascade of softly broken supersymmetric theories. We investigate the renormalization group (RG) flow of SUSY breaking terms as well as supersymmetric couplings. It is found that the magnitudes of SUSY breaking terms are suppressed in most regimes of the RG flow through the duality cascade. At one stage of cascading, the gaugino mass of the strongly coupled sector and scalar masses converge to certain values, which are determined by the gauge coupling and the gaugino mass of the weakly coupled sector. At the next stage, the strongly and weakly coupled sectors are interchanged with each other. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called B-term. © 2009 The American Physical Society.

Duality cascade of softly broken supersymmetric theories
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Kazutoshi Ohta, Yuji Omura, Haruhiko Terao
PHYSICAL REVIEW D, 79, 4, AMER PHYSICAL SOC, 2009年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the duality cascade of softly broken supersymmetric theories. We investigate the renormalization group (RG) flow of SUSY breaking terms as well as supersymmetric couplings. It is found that the magnitudes of SUSY breaking terms are suppressed in most regimes of the RG flow through the duality cascade. At one stage of cascading, the gaugino mass of the strongly coupled sector and scalar masses converge to certain values, which are determined by the gauge coupling and the gaugino mass of the weakly coupled sector. At the next stage, the strongly and weakly coupled sectors are interchanged with each other. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called B-term.

Soft supersymmetry breaking terms from A(4) lepton flavor symmetry
Hajime Ishimori, Tatsuo Kobayashi, Yuji Omura, Morimitsu Tanimoto
JOURNAL OF HIGH ENERGY PHYSICS, 12, SPRINGER, 2008年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the supersymmetric model with the A(4) lepton flavor symmetry, in particular soft supersymmetry breaking terms, which are predicted from the A(4) lepton flavor symmetry. We evaluate soft slepton masses and A-terms within the framework of supergravity theory. Constraints due to experiments of flavor changing neutral current processes are examined.

Soft supersymmetry breaking terms from A(4) lepton flavor symmetry
Hajime Ishimori, Tatsuo Kobayashi, Yuji Omura, Morimitsu Tanimoto
JOURNAL OF HIGH ENERGY PHYSICS, 12, SPRINGER, 2008年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the supersymmetric model with the A(4) lepton flavor symmetry, in particular soft supersymmetry breaking terms, which are predicted from the A(4) lepton flavor symmetry. We evaluate soft slepton masses and A-terms within the framework of supergravity theory. Constraints due to experiments of flavor changing neutral current processes are examined.

Flavor symmetry breaking and vacuum alignment on orbifolds
Tatsuo Kobayashi, Yuji Omura, Koichi Yoshioka
PHYSICAL REVIEW D, 78, 11, AMER PHYSICAL SOC, 2008年12月, ［査読有り］
英語, 研究論文（学術雑誌）, Flavor symmetry has been widely studied for figuring out the masses and mixing angles of standard model fermions. In this paper we present a framework for handling flavor symmetry breaking where the symmetry breaking is triggered by boundary conditions of scalar fields in extra-dimensional space. The alignment of scalar expectation values is achieved without referring to any details of scalar potential and its minimization procedure. As applications to non-Abelian discrete flavor symmetries, illustrative lepton mass models are constructed where the S-3 and A(4) flavor symmetries are broken down to the directions leading to the tribimaximal form of lepton mixing and realistic mass patterns.

(Non-)Abelian discrete anomalies
Takeshi Araki, Tatsuo Kobayashi, Jisuke Kubo, Saul Ramos-Sanchez, Michael Ratz, Patrick K. S. Vaudrevange
NUCLEAR PHYSICS B, 805, 1-2, 124, 147, ELSEVIER SCIENCE BV, 2008年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We derive anomaly constraints for Abelian and non-Abelian discrete symmetries using the path integral approach. We survey anomalies of discrete symmetries in heterotic orbifolds and find a new relation between such anomalies and the so-called 'anomalous' U(1). (C) 2008 Elsevier B.V. All rights reserved.

Magnetized orbifold models
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki
JOURNAL OF HIGH ENERGY PHYSICS, 9, SPRINGER, 2008年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study (4+2n)-dimensional N=1 super Yang-Mills theory on the orbifold background with non-vanishing magnetic fluxes. In particular, we study zero- modes of spinor fields. The flavor structure of our models is different from one in magnetized torus models, and would be interesting in realistic model building.

Higher order couplings from heterotic orbifold theory
Kang-Sin Choi, Tatsuo Kobayashi
NUCLEAR PHYSICS B, 797, 1-2, 295, 321, ELSEVIER SCIENCE BV, 2008年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We calculate couplings of arbitrary order from correlation functions among twisted strings, using conformal field theory. Twisted strings arise in heterotic string compactified on orbifolds yielding matter fields in the low energy limit. We calculate completely the classical and the quantum amplitude including normalization, up to a contribution from Kahler potential. The classical action has saddle points which are interpreted as worldsheet instantons described by metastable untwisted strings, formed by twisted strings distributed at certain fixed points. This understanding generalizes the area rule, in the case that the locations of twisted strings do not form a polygon, and provides a general rule for calculating these kinds of instanton corrections. An interpretation of couplings involving linearly combined states is given, which commonly appear in non-prime order orbifolds. The quantum part of the amplitude is given by ratios of gamma functions with order one arguments. (C) 2008 Elsevier B.V. All rights reserved.

Dynamically sequestered F-term uplifting in extra dimension
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura
JOURNAL OF HIGH ENERGY PHYSICS, 4, SPRINGER, 2008年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study moduli stabilization, the dynamical supersymmetry (SUSY) breaking, the uplifting of SUSY anti-de Sitter (AdS) vacuum and the sequestering of hidden sector in a five-dimensional supergravity model, where all modes of the visible sector and the hidden sector are originated from bulk fields. We clarify couplings between the visible and hidden sectors. The expressions for the visible sector soft SUSY breaking terms as well as the hidden sector potential are shown explicitly in our model. The sequestering is achieved dynamically by a wavefunction localization in extra dimension. We find that the tree-level soft scalar mass and the A-term can be suppressed at a SUSY breaking Minkowski minimum where the radius modulus is stabilized, while gaugino masses would be a mirage type.

Metastable supersymmetry breaking vacua from conformal dynamics
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura
PHYSICAL REVIEW D, 77, 6, AMER PHYSICAL SOC, 2008年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the scenario that conformal dynamics leads to metastable supersymmetry breaking vacua. At a high energy scale, the superpotential is not R-symmetric and has a supersymmetric minimum. However, conformal dynamics suppresses several operators along renormalization group flow toward the infrared fixed point. Then we can find an approximately R-symmetric superpotential, which has a metastable supersymmetry breaking vacuum, and the supersymmetric vacuum moves far away from the metastable supersymmetry breaking vacuum. We show a 4D simple model. Furthermore, we can construct 5D models with the same behavior, because of the AdS/CFT duality.

Prospects for the direct detection of neutralino dark matter in orbifold scenarios
David G. Cerdeno, Carlos Munoz, Tatsuo Kobayashi
JOURNAL OF HIGH ENERGY PHYSICS, 1, SPRINGER, 2008年01月, ［査読有り］
英語, We analyse the phenomenology of orbifold scenarios from the heterotic superstring, and the resulting theoretical predictions for the direct detection of neutralino dark matter. In particular, we study the parameter space of these constructions, computing the low-energy spectrum and taking into account the most recent experimental and astrophysical constraints, as well as imposing the absence of dangerous charge and colour breaking minima. In the remaining allowed regions the spin-independent part of the neutralino-proton cross section is calculated and compared with the sensitivity of dark matter detectors. In addition to the usual non universalities of the soft terms in orbifold scenarios due to the modular weight dependence, we also consider D-term contributions to scalar masses. These are generated by the presence of an anomalous U(1), providing more flexibility in the resulting soft terms, and are crucial in order to avoid charge and colour breaking minima. Thanks to the D-term contribution, large neutralino detection cross sections can be found, within the reach of projected dark matter detectors.

Non-perturbative moduli superpotential with positive exponents
Tatsuo Kobayashi
SUPERSYMMETRY AND THE UNIFICATION OF FUNDAMENTAL INTERACTIONS, 1078, 405, 407, AMER INST PHYSICS, 2008年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, We study nonperturbative superpotentials with positive exponents, i.e. the form like Ae(aT) with positive constant a and the modulus T.

More about F-term uplifting
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 76, 10, 2007年11月05日, ［査読有り］
英語, 研究論文（学術雑誌）, We study moduli stabilization and a realization of de Sitter vacua in generalized F-term uplifting scenarios of the Kachru-Kallosh-Linde-Trivedi-type anti-de Sitter vacuum, where the uplifting sector X directly couples to the light Kähler modulus T in the superpotential through, e.g., stringy instanton effects. F-term uplifting can be achieved by a spontaneous supersymmetry breaking sector, e.g., the Polonyi model, the O'Raifeartaigh model, and the Intriligator-Seiberg-Shih model. Several models with the X-T mixing are examined, and qualitative features in most models even with such mixing are almost the same as those in the Kachru-Kallosh-Linde-Trivedi scenario. One of the quantitative changes, which are relevant to the phenomenology, is a larger hierarchy between the modulus mass mT and the gravitino mass m3/2, i.e., mT/m3/2=O(a2), where a∼4π2. In spite of such a large mass, the modulus F term is suppressed not like FT=O(m3/2/a2), but like FT=O(m3/2/a) for ln (MPl/m3/2)∼a, because of an enhancement factor coming from the X-T mixing. Then we typically find a mirage-mediation pattern of gaugino masses of O(m3/2/a), while the scalar masses would be generically of O(m3/2). © 2007 The American Physical Society.

R-symmetry, supersymmetry breaking and metastable vacua in global and local supersymmetric theories
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura
JOURNAL OF HIGH ENERGY PHYSICS, 11, SPRINGER, 2007年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We study N=1 global and local supersymmetric theories with a continuous global U(1)(R) symmetry as models of dynamical supersymmetry (SUSY) breaking. We introduce explicit R-symmetry breaking terms into such models, in particular a generalized O'Raifeartaigh model. Such explicit R-symmetry breaking terms can lead to a SUSY preserving minimum. We classify explicit R-symmetry breaking terms by the structure of newly appeared SUSY stationary points as a consequence of the R-breaking effect, which could make the SUSY breaking vacuum metastable. We show that the R-breaking terms are basically divided into two categories. One of them does not generate a SUSY solution, or yields SUSY solutions that disappear in the case of supergravity when we tune a parameter so that the original SUSY breaking minimum becomes a Minkowski vacuum. We also show that the general argument by Nelson and Seiberg for a dynamical SUSY breaking still holds with a local SUSY except for a certain nontrivial case, and present concrete examples of the exception.

More about f-term uplifting
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi
PHYSICAL REVIEW D, 76, 10, AMER PHYSICAL SOC, 2007年11月, ［査読有り］
英語, We study moduli stabilization and a realization of de Sitter vacua in generalized F-term uplifting scenarios of the Kachru-Kallosh-Linde-Trivedi-type anti-de Sitter vacuum, where the uplifting sector X directly couples to the light Kahler modulus T in the superpotential through, e.g., stringy instanton effects. F-term uplifting can be achieved by a spontaneous supersymmetry breaking sector, e.g., the Polonyi model, the O'Raifeartaigh model, and the Intriligator-Seiberg-Shih model. Several models with the X-T mixing are examined, and qualitative features in most models even with such mixing are almost the same as those in the Kachru-Kallosh-Linde-Trivedi scenario. One of the quantitative changes, which are relevant to the phenomenology, is a larger hierarchy between the modulus mass m(T) and the gravitino mass m(3/2), i.e., m(T)/m(3/2)=O(a(2)), where a similar to 4 pi(2). In spite of such a large mass, the modulus F term is suppressed not like F-T=O(m(3/2)/a(2)), but like F-T=O(m(3/2)/a) for ln(M-Pl/m(3/2))similar to a, because of an enhancement factor coming from the X-T mixing. Then we typically find a mirage-mediation pattern of gaugino masses of O(m(3/2)/a), while the scalar masses would be generically of O(m(3/2)).

TeV scale partial mirage unification and neutralino dark matter
Hiroyuki Abe, Yeong Gyun Kim, Tatsuo Kobayashi, Yasuhiro Shimizu
JOURNAL OF HIGH ENERGY PHYSICS, 9, SPRINGER, 2007年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the TeV scale partial mirage unification scenario, where the gluino and wino masses are degenerate around a TeV scale, but the bino mass is not degenerate. This scenario has phenomenologically interesting aspects. First, because of the degeneracy between the gluino and wino masses, this scenario does not have the little hierarchy problem, that is, the higgisino mass is around 150 GeV. The lightest superparticle is a mixture of the bino and higgsino, and can lead to a right amount of thermal relic density as a dark matter candidate.

Discrete R-symmetry anomalies in heterotic orbifold models
Takeshi Araki, Kang-Sin Choi, Tatsuo Kobayashi, Jisuke Kubo, Hiroshi Ohki
PHYSICAL REVIEW D, 76, 6, AMER PHYSICAL SOC, 2007年09月, ［査読有り］
英語, Anomalies of discrete R symmetries appearing in heterotic orbifold models are studied. We find that the mixed anomalies for different gauge groups satisfy the universal Green-Schwarz condition, indicating that these anomalies are canceled by the Green-Schwarz mechanism. An exact relation between the anomaly coefficients of the discrete R symmetries and one-loop beta-function coefficients is obtained. We also find that the discrete R symmetries have a good chance to be unbroken down to the supersymmetry breaking scale. Even below this scale a Z(2) subgroup is unbroken, and it may be an origin of the R parity of the minimal supersymmetric standard model. Relations between the R-symmetry anomalies and T-duality anomalies are also investigated.

String-derived D-4 flavor symmetry and phenomenological implications
Pyungwon Ko, Tatsuo Kobayashi, Jae-Hyeon Park, Stuart Raby
PHYSICAL REVIEW D, 76, 3, AMER PHYSICAL SOC, 2007年08月, ［査読有り］
英語, 研究論文（学術雑誌）, In this paper we show how some flavor symmetries may be derived from the heterotic string, when compactified on a 6D orbifold. In the body of the paper we focus on the D-4 family symmetry, recently obtained in Z(3)xZ(2) orbifold constructions. We show how this flavor symmetry constrains fermion masses, as well as the soft SUSY breaking mass terms. Flavor symmetry breaking can generate the hierarchy of fermion masses and at the same time the flavor symmetry suppresses large flavor changing neutral current processes.

Relaxed fine-tuning in models with nonuniversal gaugino masses
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura
Physical Review D - Particles, Fields, Gravitation and Cosmology, 76, 1, 2007年07月09日, ［査読有り］
英語, 研究論文（学術雑誌）, We study, in a bottom-up approach, the fine-tuning problem between soft supersymmetry (SUSY) breaking parameters and the μ term for the successful electroweak symmetry breaking in the minimal supersymmetric standard model. It is shown that certain ratios among nonuniversal gaugino masses at the grand unified theory (GUT) scale are necessary to reduce fine-tuning. In addition, when all the gaugino masses are regarded as independent ones in their origins, a small gluino mass M3 120GeV and a nonvanishing A term At∼O(M3) associated with top squarks are also required at the GUT scale as well as the nonuniversality. On the other hand, when we consider some UV theory, which fixes ratios of soft SUSY breaking parameters as certain values aside from the overall magnitude, heavier spectra are allowed. It is favored that the gluino and W-ino masses are almost degenerate at the weak scale, while a wider region of b-ino mass is favorable. © 2007 The American Physical Society.

TeV scale mirage mediation and natural little supersymmetric hierarchy
Kiwoon Choi, Kwang Sik Jeong, Tatsuo Kobayashi, Ken-Ichi Okumura
Physical Review D - Particles, Fields, Gravitation and Cosmology, 75, 9, 2007年05月31日, ［査読有り］
英語, 研究論文（学術雑誌）, TeV scale mirage mediation has been proposed as a supersymmetry-breaking scheme reducing the fine-tuning for electroweak symmetry breaking in the minimal supersymmetric extension of the standard model. We discuss a moduli stabilization setup for TeV scale mirage mediation which allows an extradimensional interpretation for the origin of supersymmetry breaking and naturally gives a weak-scale size of the Higgs B parameter. The setup utilizes the holomorphic gauge kinetic functions depending on both the heavy dilaton and the light volume modulus whose axion partners are assumed to be periodic fields. We also examine the low-energy phenomenology of TeV scale mirage mediation, particularly the constraints from electroweak symmetry breaking and flavor changing neutral current processes. © 2007 The American Physical Society.

TeV scale mirage mediation and natural little supersymmetric hierarchy
Kiwoon Choi, Kwang Sik Jeong, Tatsuo Kobayashi, Ken-ichi Okumura
PHYSICAL REVIEW D, 75, 9, AMER PHYSICAL SOC, 2007年05月, ［査読有り］
英語, TeV scale mirage mediation has been proposed as a supersymmetry-breaking scheme reducing the fine-tuning for electroweak symmetry breaking in the minimal supersymmetric extension of the standard model. We discuss a moduli stabilization setup for TeV scale mirage mediation which allows an extradimensional interpretation for the origin of supersymmetry breaking and naturally gives a weak-scale size of the Higgs B parameter. The setup utilizes the holomorphic gauge kinetic functions depending on both the heavy dilaton and the light volume modulus whose axion partners are assumed to be periodic fields. We also examine the low-energy phenomenology of TeV scale mirage mediation, particularly the constraints from electroweak symmetry breaking and flavor changing neutral current processes.

Stringy origin of non-Abelian discrete flavor symmetries
Tatsuo Kobayashi, Hans Peter Nilles, Felix Ploeger, Stuart Raby, Michael Ratz
NUCLEAR PHYSICS B, 768, 1-2, 135, 156, ELSEVIER SCIENCE BV, 2007年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the origin of non-Abelian discrete flavor symmetries in superstring theory. We classify all possible non-Abelian discrete flavor symmetries which can appear in heterotic orbifold models. These symmetries include D-4 and Delta(54). We find that the symmetries of the couplings are always larger than the symmetries of the compact space. This is because they are a consequence of the geometry of the orbifold combined with the space group selection rules of the string. We also study possible breaking patterns. Our analysis yields a simple geometric understanding of the realization of non-Abelian flavor symmetries. (c) 2007 Elsevier B.V. All rights reserved.

Non-factorisable Z(2) x Z(2) heterotic orbifold models and Yukawa couplings
Stefan Forste, Tatsuo Kobayashi, Hiroshi Ohki, Kei-jiro Takahashi
JOURNAL OF HIGH ENERGY PHYSICS, 3, SPRINGER, 2007年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We classify compactification lattices for supersymmetric Z(2) x Z(2) orbifolds. These lattices include factorisable as well as non-factorisable six-tori. Different models lead to different numbers of fixed points/tori. A lower bound on the number of fixed tori per twisted sector is given by four, whereas an upper bound consists of 16 fixed tori per twisted sector. Thus, these models have a variety of generation numbers. For example, in the standard embedding, the smallest number of net generations among these classes of models is equal to six, while the largest number is 48. Conditions for allowed Wilson lines and Yukawa couplings are derived.

Time variation of the proton-electron mass ratio and the fine structure constant with a runaway dilaton
Takeshi Chiba, Tatsuo Kobayashi, Masahide Yamaguchi, Jun'ichi Yokoyama
Physical Review D - Particles, Fields, Gravitation and Cosmology, 75, 4, 2007年02月20日, ［査読有り］
英語, 研究論文（学術雑誌）, Recent astrophysical observations indicate that the proton-electron mass ratio and the fine structure constant have gone through nontrivial time evolution. We discuss their time variation in the context of a dilaton runaway scenario with gauge coupling unification at the string scale Ms. We show that the choice of adjustable parameters allows them to fit the same order magnitude of both variations and their (opposite) signs in such a scenario. © 2007 The American Physical Society.

Moduli stabilization, F-term uplifting, and soft supersymmetry breaking terms
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura
PHYSICAL REVIEW D, 75, 2, AMERICAN PHYSICAL SOC, 2007年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study moduli stabilization with F-term uplifting. As a source of uplifting F-term, we consider spontaneous supersymmetry breaking models, e.g. the Polonyi model and the Intriligator-Seiberg-Shih model. We analyze potential minima by requiring almost vanishing vacuum energy and evaluate the size of modulus F-term. We also study soft SUSY-breaking terms. In our scenario, the mirage mediation is dominant in gaugino masses. Scalar masses can be comparable with gaugino masses or much heavier, depending on couplings with spontaneous supersymmetry breaking sector.

Dynamical realization of democratic Yukawa matrices and alignment of A terms
Tatsuo Kobayashi, Yuji Omura, Haruhiko Terao
PHYSICAL REVIEW D, 74, 5, AMERICAN PHYSICAL SOC, 2006年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study realization of the democratic form of Yukawa matrices by infrared fixed points. We investigate renormalization-group flows of Yukawa couplings in models with a single Yukawa matrix for three families, and up and down-sector Yukawa matrices. It is found that each model has its certain pattern of renormalization-group flows of Yukawa matrices. We apply them to the charged lepton sector and quark sector, and examine in which situation our class of models can lead to realistic results for the mass ratios and mixing angles between the second and third families. We also study corresponding A-terms. The A-terms approach toward the universal form with no physical CP-violating phase. Thus, constraints due to various neutral flavor changing processes except for mu -> e gamma are found to be satisfied by this dynamics. In order to suppress the electric dipole moments as well as mu -> e gamma sufficiently, more alignment of the A-terms with some reason is required.

Remark on integrating out heavy moduli in flux compactification
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi
PHYSICAL REVIEW D, 74, 4, AMERICAN PHYSICAL SOC, 2006年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We study two steps of moduli stabilization in type IIB flux compactification with gaugino condensations. We consider the condition that one can integrate out heavy moduli first with light moduli remaining. We give appendix, where detail study is carried out for potential minima of the model with a six dimensional compact space with h(1,1)=h(2,1)=1, including the model, whose respective moduli with h(1,1),h(2,1)not equal 1 are identified.

Fine-tuning in gauge mediated supersymmetry breaking models and induced top Yukawa coupling
Tatsuo Kobayashi, Haruhiko Terao, Akito Tsuchiya
PHYSICAL REVIEW D, 74, 1, AMER PHYSICAL SOC, 2006年07月, ［査読有り］
英語, 研究論文（学術雑誌）, It is shown that fine-tuning of the Higgs parameters stronger than a few percent is required at best in the models with gauge mediated supersymmetry breaking. With the aim of solving this problem, we consider a new type of models in which the top Yukawa coupling is induced at TeV scale through mass mixing with unknown matter fields. Then it is found that the fine-tuning problem can be eliminated essentially. We discuss some phenomenological features of this model and also consider the extension to the next-to-minimal models.

Moduli-mixing racetrack model
H Abe, T Higaki, T Kobayashi
NUCLEAR PHYSICS B, 742, 187, 207, ELSEVIER SCIENCE BV, 2006年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study supersymmetric models with double gaugino condensations in the hidden sector, where the gauge couplings depend on two light moduli of superstring theory. We perform a detailed analysis of this class of model and show that there is no stable supersymmetric minimum with finite vacuum values of moduli fields. Instead, we find that the supersymmetry breaking occurs with moduli stabilized and negative vacuum energy. That yields moduli-dominated soft supersymmetry breaking terms. To realize slightly positive (or vanishing) vacuum energy, we add uplifting potential. We discuss uplifting does not change qualitatively the vacuum expectation values of moduli and the above feature of supersymmetry breaking. (c) 2006 Elsevier B.V. All rights reserved.

Little SUSY hierarchy in mixed modulus-anomaly mediation
K Choi, KS Jeong, T Kobayashi, K Okumura
PHYSICS LETTERS B, 633, 2-3, 355, 361, ELSEVIER SCIENCE BV, 2006年02月, ［査読有り］
英語, 研究論文（学術雑誌）, Motivated by the KKLT string compactification involving a supersymmetry-breaking uplifting potential, we examine 4D effective supergravity with a generic form of uplifting potential, focusing on the possibility that the resulting mixed modulus-anomaly mediated soft terms realize the little hierarchy between the Higgs boson masses m(H) and the sparticle masses m(SUSY). It is noted that for some type of uplifting potential, the anomaly-mediated contribution to m(H)(2) at M-GUT can cancel the subsequent renormalization group evolution of m(H)(2) down to TeV scale, thereby the model can naturally realize the little hierarchy m(H)(2) similar to m(SUSY)(2)/8 pi(2) which is desirable for the lightest Higgs boson mass to satisfy the experimental bound. In such models, the other Higgs mass parameters mu and B can have the desirable size mu similar to B similar to mH without severe fine-tuning of parameters, although the gravitino is much heavier than the Higgs boson. Those models for the little hierarchy avoid naturally the dangerous SUSY flavor and CP violations, and predict nearly degenerate low energy gaugino masses, pure Higgsino LSP and also a specific relation between the stop and gaugino masses. (c) 2005 Elsevier B.V. All rights reserved.

More about soft terms and FCNC in realistic string constructions
T Kobayashi, C Munoz
JOURNAL OF HIGH ENERGY PHYSICS, 1, SPRINGER, 2006年01月, ［査読有り］
英語, 研究論文（学術雑誌）, In realistic four-dimensional string constructions the presence of anomalous U(1)'s is generic. In addition, the associated Fayet-Iliopoulos contribution to the D-term can break the extra gauge symmetries. As a consequence, physical particles can appear combined with other states. We show that even if a three-generation standard-like model has originally flavour-independent soft scalar masses, the particle mixing contribution may generate non-universality among them. Thus FCNC effects which were apparently absent reappear. We also discuss the size of these contributions in an explicit model, and how they can be suppressed.

Kachru-Kallosh-Linde-Trivedi-type models with moduli-mixing superpotential
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 73, 4, 2006年, ［査読有り］
英語, 研究論文（学術雑誌）, We study KKLT type models with moduli-mixing superpotential. In several string models, gauge kinetic functions are written as linear combinations of two or more moduli fields. Their gluino condensation generates moduli-mixing superpotential. We assume one of moduli fields is frozen already around the string scale. It is found that Kähler modulus can be stabilized at a realistic value without tuning 3-form fluxes because of gluino condensation on (non-)magnetized D-brane. Furthermore, we do not need to highly tune parameters in order to realize a weak gauge coupling and a large hierarchy between the gravitino mass and the Planck scale, when there exists nonperturbative effects on D3-brane. SUSY breaking patterns in our models have a rich structure. Also, some of our models have cosmologically important implications, e.g., on the overshooting problem and the destabilization problem due to finite temperature effects as well as the gravitino problem and the moduli problem. © 2006 The American Physical Society.

Fine-tuning in gauge mediated supersymmetry breaking models and induced top Yukawa coupling
Tatsuo Kobayashi, Haruhiko Terao, Akito Tsuchiya
Physical Review D - Particles, Fields, Gravitation and Cosmology, 74, 1, 2006年, ［査読有り］
英語, 研究論文（学術雑誌）, It is shown that fine-tuning of the Higgs parameters stronger than a few percent is required at best in the models with gauge mediated supersymmetry breaking. With the aim of solving this problem, we consider a new type of models in which the top Yukawa coupling is induced at TeV scale through mass mixing with unknown matter fields. Then it is found that the fine-tuning problem can be eliminated essentially. We discuss some phenomenological features of this model and also consider the extension to the next-to-minimal models. © 2006 The American Physical Society.

Flavor structure and coupling selection rule from intersecting D-branes
T Higaki, N Kitazawa, T Kobayashi, K Takahashi
PHYSICAL REVIEW D, 72, 8, AMERICAN PHYSICAL SOC, 2005年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study flavor structure and the coupling selection rule in intersecting D-brane configurations on T(2)xT(2)xT(2) as well as its orbifold/orientifold compactifications. We formulate the selection rule for Yukawa couplings and its extensions to generic n-point couplings. We investigate the possible flavor structure, which can appear from intersecting D-brane configuration. Then, we show there is a certain rule among intersecting numbers for states corresponding to allowed Yukawa couplings, and also it is found that their couplings are determined by discrete Abelian symmetries. Our studies on the flavor structure and the coupling selection rule in this class of models show that there is no solution to derive realistic Yukawa matrices only from stringy 3-point couplings at the tree-level within the framework of the minimal matter content of the supersymmetric standard model.

Induced top-Yukawa coupling and suppressed Higgs mass parameters
T Kobayashi, H Nakano, H Terao
PHYSICAL REVIEW D, 71, 11, AMER PHYSICAL SOC, 2005年06月, ［査読有り］
英語, 研究論文（学術雑誌）, In the scenarios with heavy top squarks, mass parameters of the Higgs field must be fine-tuned due to a large logarithmic correction to the soft scalar mass. We consider a new possibility that the top-Yukawa coupling is small above TeV scale. The large top mass is induced from strong Yukawa interaction of the Higgs with another gauge sector, in which supersymmetry breaking parameters are given to be small. Then it is found that the logarithmic correction to the Higgs soft scalar mass is suppressed in spite of the strong coupling, and the fine-tuning is ameliorated. We propose an explicit model coupled to a superconformal gauge theory which realizes the above situation.

Induced top-Yukawa coupling and suppressed Higgs mass parameters
Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao
Physical Review D - Particles, Fields, Gravitation and Cosmology, 71, 11, American Physical Society, 2005年06月01日, ［査読有り］
英語, 研究論文（学術雑誌）, In the scenarios with heavy top squarks, mass parameters of the Higgs field must be fine-tuned due to a large logarithmic correction to the soft scalar mass. We consider a new possibility that the top-Yukawa coupling is small above TeV scale. The large top mass is induced from strong Yukawa interaction of the Higgs with another gauge sector, in which supersymmetry breaking parameters are given to be small. Then it is found that the logarithmic correction to the Higgs soft scalar mass is suppressed in spite of the strong coupling, and the fine-tuning is ameliorated. We propose an explicit model coupled to a superconformal gauge theory which realizes the above situation. © 2005 The American Physical Society.

Lepton masses and mixing angles from heterotic orbifold models
P Ko, T Kobayashi, JH Park
PHYSICAL REVIEW D, 71, 9, AMER PHYSICAL SOC, 2005年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We systematically study the possibility for realizing realistic values of lepton mass ratios and mixing angles by using only renormalizable Yukawa couplings derived from the heterotic Z(6)-I orbifold. We assume one pair of up and down sector Higgs fields. We consider both the Dirac neutrino mass scenario and the seesaw scenario with degenerate right-handed majorana neutrino masses. It is found that realistic values of the charged lepton mass ratios, m(e)/m(tau) and m(mu)/m(tau), the neutrino mass squared difference ratio, Delta m(31)(2)/Delta m(21)(2), and the lepton mixing angles can be obtained in certain cases.

Democratic mass matrices induced by strong gauge dynamics and large mixing angles for leptons
T Kobayashi, H Shirano, H Terao
PROGRESS OF THEORETICAL PHYSICS, 113, 5, 1077, 1099, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2005年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider the dynamical realization of the democratic type of Yukawa coupling matrices as the Pendelton-Ross infrared fixed points. Such fixed points of the Yukawa couplings become possible through the introduction of many Higgs fields, which are made superheavy, but one massless mode. Explicitly, we consider a strongly coupled supersymmetric GUT based on SU(5) x SU(5), in which rapid convergence to the infrared fixed point generates sufficiently large mass hierarchy for quarks and leptons. In particular, it is found that the remarkable difference between mixing angles in the quark and lepton sectors can be explained as a simple dynamical consequence. We also discuss a possible scenario leading to a realistic mass spectra and mixing angles for quarks and leptons. In this scheme, the Yukawa couplings not only for top but also for bottom appear close to their quasi-fixed points at low energy and, therefore, tan beta should be large.

Lepton masses and mixing angles from heterotic orbifold models
Pyungwon Ko, Tatsuo Kobayashi, Jae-Hyeon Park
Physical Review D - Particles, Fields, Gravitation and Cosmology, 71, 9, 1, 9, 2005年05月01日, ［査読有り］
英語, 研究論文（学術雑誌）, We systematically study the possibility for realizing realistic values of lepton mass ratios and mixing angles by using only renormalizable Yukawa couplings derived from the heterotic Z6-I orbifold. We assume one pair of up and down sector Higgs fields. We consider both the Dirac neutrino mass scenario and the seesaw scenario with degenerate right-handed majorana neutrino masses. It is found that realistic values of the charged lepton mass ratios, me/mτ and mμ/mτ, the neutrino mass squared difference ratio, Δm312/ Δm212, and the lepton mixing angles can be obtained in certain cases. © 2005 The American Physical Society.

Yukawa coupling structure in intersecting D-brane models
N Kitazawa, T Kobayashi, N Maru, N Okada
EUROPEAN PHYSICAL JOURNAL C, 40, 4, 579, 587, SPRINGER, 2005年04月, ［査読有り］
英語, 研究論文（学術雑誌）, The structure of Yukawa coupling matrices is investigated in type IIA T-6/(Z(2) x Z(2)) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T-6 = T-2 x T-2 x T-2. We study the new type of favor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic.

Large mass scale by strong gauge dynamics with infrared fixed point
T Kobayashi, H Nakano, H Terao, Y Yamada
PROGRESS OF THEORETICAL PHYSICS, 113, 2, 413, 427, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2005年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider a mechanism for realizing the desired decoupling of the strongly-coupled sector which is supposed to generate hierarchical structure of the Yukawa couplings. In our mechanism, the same strongly-coupled sector is responsible for generating a sufficiently flat potential and a large vacuum expectation value (VEV) of a gauge-singlet scalar field by suppressing its soft scalar mass and self-coupling. A vacuum instability is caused by a supersymmetry-breaking A-term of order 10 TeV. We explicitly demonstrate the infrared convergence of soft scalar masses due to strongly-coupled dynamics and show that the soft mass of the singlet is at most of the same order as the soft masses of squarks and sleptons, Which are much more strongly suppressed than the A-term. The physical mass scale of the decoupling is calculated in a self-consistent way. We also reinterpret the result in terms of an RG-improved effective potential.

Searching for realistic 4d string models with Pati-Salam symmetry
Orbifold grand uni#12;ed theories from heterotic string compacti#12;cation on a Z6 orbifold, 2005年, ［査読有り］

Radiative stabilization of warped space
T Kobayashi, K Yoshioka
JOURNAL OF HIGH ENERGY PHYSICS, 11, SPRINGER, 2004年11月, ［査読有り］
英語, Higher-dimensional field theory has been applied to explore various issues in recent particle physics such as the gauge hierarchy problem. In order for such approaches to be viable, a crucial ingredient is to fix the sizes of extra dimensions at some finite values, which sizes are generically free parameters in the theory. In this paper, we present several schemes to determine the radius of extra dimension in warped five-dimensional theory. In every case, a non-vanishing Fayet-Iliopoulos term for abelian gauge factor plays a crucial role for the radius stabilization. It is radiatively generated in the presence of charged matter fields and the compactification is therefore spontaneous, not forced by selected operators. The low-energy supersymmetry is broken or unbroken, and the radius can be fixed to give a small or large scale hierarchy without any fine tuning of parameters. We also discuss a model of the radius stabilization correlated with Yukawa hierarchy and supersymmetry breaking.

Quark masses and mixing angles in heterotic orbifold models
P Ko, T Kobayashi, JH Park
PHYSICS LETTERS B, 598, 3-4, 263, 272, ELSEVIER SCIENCE BV, 2004年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study systematically the possibility for realizing realistic values of quark mass ratios m(c)/m(t) and m(s)/m(b) and the mixing angle V-cb by using only renormalizable Yukawa couplings derived from heterotic orbifold models. We assume one pair of up and down sector Higgs fields. We find many realistic Yukawa matrices. (C) 2004 Published by Elsevier B.V.

Suppressed supersymmetry breaking terms in the Higgs sector
T Kobayashi, H Terao
JOURNAL OF HIGH ENERGY PHYSICS, 7, SPRINGER, 2004年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the little hierarchy between mass parameters in the Higgs sector and other SUSY breaking masses. This type of spectrum can relieve the fine-tuning problem in the MSSM Higgs sector. Our scenario can be realized by superconformal dynamics. The spectrum in our scenario has significant implications in other phenomenological aspects like the relic abundance of the lightest neutralino and relaxation of the unbounded-from-below constraints.

D-term inflation and nonperturbative Kahler potential of dilaton
T Higaki, T Kobayashi, O Seto
JOURNAL OF HIGH ENERGY PHYSICS, 7, SPRINGER, 2004年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the D-term inflation scenario with a nonperturbative Kahler potential of the dilaton field. Although the FI term which leads an inflationary expansion is given by the derivative of the Kahler potential with respect to the dilaton in heterotic string models with anomalous U(1), the too large magnitude is problematic for a viable D-term inflation. In this paper, we point out that the Kahler potential with a nonperturbative term can reduce the magnitude of FI term to desired values while both the dilaton stabilization and D-term domination in the potential are realized by nonperturbative superpotential.

Constructing 5d orbifold grand unified theories from heterotic strings
T Kobayashi, S Raby, RJ Zhang
PHYSICS LETTERS B, 593, 262, 270, ELSEVIER SCIENCE BV, 2004年07月, ［査読有り］
英語, 研究論文（学術雑誌）, A three-generation Pati-Salam model is constructed by compactifying the heterotic string on a particular T-6/Z(6) Abelian symmetric orbifold with two discrete Wilson lines. The compactified space is taken to be the Lie algebra lattice G(2) circle plus SU(3) circle plus SO(4). When one dimension of the SO(4) lattice is large compared to the string scale, this model reproduces many features of a 5d SO(10) grand unified theory compactified on an S-1/Z(2) orbifold. (Of course, with two large extra dimensions we can obtain a 6d SO(10) grand unified theory.) We identify the orbifold parities and other ingredients of the orbifold grand unified theories in the string model. Our construction provides a UV completion of orbifold grand unified theories, and gives new insights into both field theoretical and string theoretical constructions. (C) 2004 Elsevier B.V. All rights reserved.

Supersymmetry breaking in warped geometry
K Choi, DY Kim, IW Kim, T Kobayashi
EUROPEAN PHYSICAL JOURNAL C, 35, 2, 267, 275, SPRINGER, 2004年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS(5) which generate the hierarchical Yukawa couplings by dynamically quasi-localizing the bulk matter fields in an extra dimension. Such models can be regarded as the AdS dual of the recently studied 4-dimensional models which contain a supersymmetric CFT to generate the hierarchical Yukawa couplings. In such models, if supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous flavor-violating soft parameters are suppressed with an appropriate correlation with the Yukawa coupling suppression, thereby avoiding the SUSY flavor problem in a natural manner. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework, and discuss the constraints from flavor-changing rare processes. Most of the discussions in this paper can be applied also to models with a flat extra dimension in which the Yukawa hierarchy is generated by quasi-localizing the bulk matter fields in the extra dimension.

Anomalous U(1) D-term contribution in type I string models
T Higaki, Y Kawamura, T Kobayashi, H Nakano
PHYSICAL REVIEW D, 69, 8, AMER PHYSICAL SOC, 2004年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the D-term contribution for anomalous U(1) symmetries in type I string models and derive a general formula for the D-term contribution, assuming that the dominant source of supersymmetry breaking is given by the F terms of the dilaton, (overall) moduli, or twisted moduli fields. On the basis of the formula, we also point out that there are several features different from the case of heterotic string models. The differences originate from the different forms of the Kahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models.

Non-perturbative Kahler potential, dilaton stabilization and Fayet-Iliopoulo term
T Higaki, Y Kawamura, T Kobayashi, H Nakano
PHYSICS LETTERS B, 582, 3-4, 257, 262, ELSEVIER SCIENCE BV, 2004年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the dilaton stabilization in models with anomalous U(l) symmetry by adding specific string-motivated, non-perturbative corrections to the tree-level dilaton Kahler potential. We find that the non-perturbative effects can stabilize the dilaton at a desirably large value. We also observe that the size of Fayet-Iliopoulos term is reduced at the stabilized point. (C) 2004 Published by Elsevier B.V.

Localization of heterotic anomalies on various hypersurfaces of [Formula Presented]
Stefan Groot Nibbelink, Mark Hillenbach, Tatsuo Kobayashi, Martin G. A. Walter
Physical Review D - Particles, Fields, Gravitation and Cosmology, 69, 4, 2004年02月13日, ［査読有り］
英語, 研究論文（学術雑誌）, We investigate the structure of local anomalies of heterotic [Formula Presented] theory on [Formula Presented] We show that the untwisted states lead to anomalies in 10, four, and in particular six dimensions. At each of the six dimensional fixed spaces of this orbifold the twisted states ensure, that the anomalies factorize separately. As some of these twisted states live on [Formula Presented] they give rise to four dimensional anomalies as well. At all four dimensional fixed points at worst a single Abelian anomaly can arise. Additionally we show that the anomalies in all these dimensions factorize in a universal way and can be canceled simultaneously. © 2004 The American Physical Society.

Localization of heterotic anomalies on various hypersurfaces of T-6/Z(4)
SG Nibbelink, M Hillenbach, T Kobayashi, MGA Walter
PHYSICAL REVIEW D, 69, 4, AMERICAN PHYSICAL SOC, 2004年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We investigate the structure of local anomalies of heterotic E(8)xE'(8) theory on T-6/Z(4). We show that the untwisted states lead to anomalies in 10, four, and in particular six dimensions. At each of the six dimensional fixed spaces of this orbifold the twisted states ensure, that the anomalies factorize separately. As some of these twisted states live on T-2/Z(2), they give rise to four dimensional anomalies as well. At all four dimensional fixed points at worst a single Abelian anomaly can arise. Additionally we show that the anomalies in all these dimensions factorize in a universal way and can be canceled simultaneously.

Dilaton and moduli fields in D-term inflation
T Kobayashi, O Seto
PHYSICAL REVIEW D, 69, 2, AMER PHYSICAL SOC, 2004年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We investigate the possibility of D-term inflation within the framework of type-I string-inspired models. Although the D-term inflation model has the excellent property that it is free of the so-called eta problem, two serious problems appear when we embed D-term inflation in string theory: the magnitude of the FI term and the rolling motion of the dilaton. In the present paper, we analyze the potential of D-term inflation in type-I-inspired models and study the behavior of dilaton and twisted moduli fields. Adopting the nonperturbative superpotential induced by gaugino condensation, the twisted moduli can be stabilized. If the dilaton is in a certain range, it evolves very slowly and does not run away to infinity. Thus D-term-dominated vacuum energy becomes available for driving inflation. By studying the density perturbation generated by the inflation model, we derive the constraints on model parameters and give some implications on D-term inflation in type-I-inspired models.

Anomalous [Formula Presented] D-term contribution in type I string models
Tetsutaro Higaki, Yoshiharu Kawamura, Tatsuo Kobayashi, Hiroaki Nakano
Physical Review D - Particles, Fields, Gravitation and Cosmology, 69, 8, 9, 2004年, ［査読有り］
英語, 研究論文（学術雑誌）, We study the D-term contribution for anomalous [Formula Presented] symmetries in type I string models and derive a general formula for the D-term contribution, assuming that the dominant source of supersymmetry breaking is given by the F terms of the dilaton, (overall) moduli, or twisted moduli fields. On the basis of the formula, we also point out that there are several features different from the case of heterotic string models. The differences originate from the different forms of the Kähler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models. © 2004 The American Physical Society.

Anomalous U(1) D-term contribution in type i string models
Tetsutaro Higaki, Yoshiharu Kawamura, Tatsuo Kobayashi, Hiroaki Nakano
Physical Review D, 69, 8, 2004年, ［査読有り］
英語, 研究論文（学術雑誌）, We study the D-term contribution for anomalous U(1) symmetries in type I string models and derive a general formula for the D-term contribution, assuming that the dominant source of supersymmetry breaking is given by the F terms of the dilaton, (overall) moduli, or twisted moduli fields. On the basis of the formula, we also point out that there are several features different from the case of heterotic string models. The differences originate from the different forms of the Kahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models. © 2004 The American Physical Society.

Exact S3 symmetry solving the supersymmetric flavor problem
Tatsuo Kobayashi, Jisuke Kubo, Haruhiko Terao
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 568, 1-2, 83, 91, Elsevier, 2003年08月21日, ［査読有り］
英語, 研究論文（学術雑誌）, The exact discrete flavor symmetry, S3 in the hadronic sector and S3 x Z2 in the leptonic sector, which has been recently found, is introduced in a supersymmetric extension of the standard model. We investigate the supersymmetric flavor problem, and explicitly find that thanks to the flavor symmetry the dangerous FCNC processes and CP-violating phases are sufficiently suppressed. © 2003 Elsevier B.V. All rights reserved.

Twisted moduli stabilization in type I string models
T Higaki, T Kobayashi
PHYSICAL REVIEW D, 68, 4, AMER PHYSICAL SOC, 2003年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We consider a model with dilaton and twisted moduli fields, which is inspired by type I string models. The stabilization of their vacuum expectation values is studied. We find that the stabilization of the twisted moduli field has different aspects from dilaton stabilization.

Flavor violation in supersymmetric theories with gauged flavor symmetries
T Kobayashi, H Nakano, H Terao, K Yoshioka
PROGRESS OF THEORETICAL PHYSICS, 110, 2, 247, 267, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2003年08月, ［査読有り］
英語, In this paper, we study flavor violation in supersymmetric models with gauged flavor symmetries. There are several sources of flavor violation in these theories. The dominant flavor violation is the tree-level D-term contribution to scalar masses generated by flavor symmetry breaking. We present a new approach for suppressing these phenomenologically dangerous effects by separating the flavor-breaking sector from the supersymmetry-breaking sector. This separation can be achieved either in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor symmetries can yield sizable generation-dependent masses of scalars. Generically the gaugino mass effects are not suppressed, even if the dominant D-term contribution is suppressed. We also analyze the constraints on the flavor symmetry sector resulting from these flavor-violating corrections.

Heterotic Yukawa couplings and continuous Wilson lines
T Kobayashi, O Lebedev
PHYSICS LETTERS B, 566, 1-2, 164, 170, ELSEVIER SCIENCE BV, 2003年07月, ［査読有り］
英語, 研究論文（学術雑誌）, Realistic heterotic string models require the presence of the Wilson lines. We study the effect of continuous Wilson lines on the heterotic Yukawa couplings for Abelian orbifold compactifications and find that the presence of continuous Wilson lines affects the magnitude of the twisted Yukawa couplings resulting in their stronger hierarchy. (C) 2003 Published by Elsevier B.V.

Heterotic string backgrounds and CP violation
T Kobayashi, O Lebedev
PHYSICS LETTERS B, 565, 1-4, 193, 200, ELSEVIER SCIENCE BV, 2003年07月, ［査読有り］
英語, 研究論文（学術雑誌）, In the framework of Z(N) orbifolds, we discuss effects of heterotic string backgrounds including discrete Wilson lines on the Yukawa matrices and their connection to CP violation. (C) 2003 Published by Elsevier B.V.

Four-dimensional construction of bulk supersymmetry breaking
T Kobayashi, N Maru, K Yoshioka
EUROPEAN PHYSICAL JOURNAL C, 29, 2, 277, 284, SPRINGER-VERLAG, 2003年07月, ［査読有り］
英語, 研究論文（学術雑誌）, In this letter, we discuss a four-dimensional model with modulus fields which are responsible for supersymmetry breaking. Given a non-trivial moduli dependence of the action, the model is found to give a proper description of higher-dimensional supersymmetry breaking. We explicitly calculate the gaugino and scalar mass spectrum and show that several classes of scenarios proposed in the literature are described in certain regions of the parameter space of the moduli vacuum expectation values. The model in other generic regions of the moduli space gives unexplored scenarios (mass spectra) of supersymmetry breaking in four dimensions.

Wave-function profile and SUSY breaking in 5D model with Fayet-Iliopoulos terms
H Abe, T Higaki, T Kobayashi
PROGRESS OF THEORETICAL PHYSICS, 109, 5, 809, 830, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2003年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We systematically study VEVs of a gauge scalar field Sigma in a bulk U(1) vector multiplet and scalar fields in brane/bulk hypermultiplets charged under U(1) in the 5D S-1/Z(2) orbifold model with generic FI terms. A non-trivial VEV of Sigma generates bulk mass terms for U(1) charged fields, and their zero modes have non-trivial profiles. In particular, in the SUSY-breaking case, bosonic and fermionic zero modes have Gaussian profiles. Such non-trivial profiles are useful to explain hierarchical couplings. A toy model for SUSY breaking is studied, and it yields sizable D-term contributions to scalar masses. Because the overall magnitude of D-term contributions is the same everywhere in the bulk and also on both branes, we have to take into account these contributions and other SUSY-breaking terms to obtain a realistic description. We also give profiles and mass eigenvalues of higher modes.

Yukawa hierarchy transfer based on superconformal dynamics and geometrical realization in string models
T Kobayashi, H Nakano, T Noguchi, H Terao
JOURNAL OF HIGH ENERGY PHYSICS, 2, SPRINGER, 2003年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a scenario that leads to hierarchical Yukawa couplings and degenerate sfermion masses at the same time, in the context of extra-dimensional models, which can be naturally embedded in a wide class of string models. The hierarchy of Yukawa couplings and degeneracy of sfermion masses can be realized thanks to superconformal gauge dynamics. The sfermion mass degeneracy is guaranteed by taking the superconformal fixed point to be family independent. In our scenario, the origin of Yukawa hierarchy is attributed to geometry of compactified dimensions and the consequent volume dependence of gauge couplings in the superconformal sectors. The difference in these gauge couplings is dynamically transferred to the hierarchy of the Yukawa couplings. Thus, our scenario combines a new dynamical approach and the conventional geometrical approach of the supersymmetric flavor problem.

Field localization in warped gauge theories
H Abe, T Kobayashi, N Maru, K Yoshioka
PHYSICAL REVIEW D, 67, 4, AMERICAN PHYSICAL SOC, 2003年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We present four-dimensional gauge theories that describe physics on five-dimensional curved (warped) backgrounds, which includes bulk fields with various spins (vectors, spinors, and scalars). Field theory on the AdS(5) geometry is examined as a simple example of our formulation. Various properties of bulk fields on this background, e.g., the mass spectrum and field localization behavior, can be achieved within a fully four-dimensional framework. Moreover, that gives a localization mechanism for massless vector fields. We also consider supersymmetric cases, and show in particular that the conditions on bulk masses imposed by supersymmetry on warped backgrounds are derived from a four-dimensional supersymmetric theory on the flat background. As a phenomenological application, models are shown to generate hierarchical Yukawa couplings. Finally, we discuss possible underlying mechanisms which dynamically realize the required couplings to generate curved geometries.

Finite theories and the supersymmetry flavor problem
K. S. Babu, Tatsuo Kobayashi, Jisuke Kubo
Physical Review D - Particles, Fields, Gravitation and Cosmology, 67, 7, 2003年, ［査読有り］
英語, 研究論文（学術雑誌）, We study a finite [Formula Presented] grand unified model based on the non-Abelian discrete symmetry [Formula Presented] This model leads to the democratic structure of the mass matrices for the quarks and leptons. In the soft supersymmetry breaking sector, the scalar trilinear couplings are aligned and the soft scalar masses are degenerate, thus solving the SUSY flavor problem. © 2003 The American Physical Society.

Field localization in warped gauge theories
Hiroyuki Abe, Tatsuo Kobayashi, Nobuhito Maru, Koichi Yoshioka
Physical Review D - Particles, Fields, Gravitation and Cosmology, 67, 4, 2003年, ［査読有り］
英語, 研究論文（学術雑誌）, We present four-dimensional gauge theories that describe physics on five-dimensional curved (warped) backgrounds, which includes bulk fields with various spins (vectors, spinors, and scalars). Field theory on the (Formula presented) geometry is examined as a simple example of our formulation. Various properties of bulk fields on this background, e.g., the mass spectrum and field localization behavior, can be achieved within a fully four-dimensional framework. Moreover, that gives a localization mechanism for massless vector fields. We also consider supersymmetric cases, and show in particular that the conditions on bulk masses imposed by supersymmetry on warped backgrounds are derived from a four-dimensional supersymmetric theory on the flat background. As a phenomenological application, models are shown to generate hierarchical Yukawa couplings. Finally, we discuss possible underlying mechanisms which dynamically realize the required couplings to generate curved geometries. © 2003 The American Physical Society.

Yukawa hierarchy transfer from the superconformal sector and degenerate sfermion masses
Tatsuo Kobayashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 65, 1, 2002年12月11日, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a new type of supersymmetric model coupled to superconformal (SC) field theories, leading simultaneously to hierarchical Yukawa couplings and completely degenerate sfermion masses. We consider models with an extra Abelian gauge symmetry to generate hierarchical structure for couplings between the standard model (SM) sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of model, the flavor-independent structure of the superconformal fixed point guarantees that the sfermion masses of the first and the second generations are completely degenerate at low energy. © 2001 The American Physical Society.

Sfermion mass degeneracy, superconformal dynamics, and supersymmetric grand unified theories
Tatsuo Kobayashi, Hiroaki Nakano, Tatsuya Noguchi, Haruhiko Terao
Physical Review D - Particles, Fields, Gravitation and Cosmology, 66, 9, 2002年11月25日, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss issues in a scenario where hierarchical Yukawa couplings are generated through the strong dynamics of superconformal field theories (SCFTs). Independently of the mediation mechanism of supersymmetry breaking, the infrared convergence property of SCFTs can provide an interesting solution to the supersymmetric flavor problem
sfermion masses are suppressed around the decoupling scale of SCFTs and eventually become degenerate to some degree, thanks to family-independent radiative corrections governed by the gaugino masses of the minimal supersymmetric standard model (MSSM). We discuss under what conditions the degeneracy of the sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then explicitly study sfermion mass degeneracy within the framework of grand unified theories coupled to SCFTs. It is found that the degeneracy for right-handed sleptons becomes worse in the conventional SU(5) model than in the MSSM. On the other hand, in the flipped (Formula presented) model, each right-handed lepton is still an SU(5) singlet, whereas the B-ino mass (Formula presented) is determined by two independent gaugino masses of (Formula presented) These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate on how further improvement can be obtained in the SCFT approach. © 2002 The American Physical Society.

Sfermion mass degeneracy, superconformal dynamics, and supersymmetric grand unified theories
T Kobayashi, H Nakano, T Noguchi, H Terao
PHYSICAL REVIEW D, 66, 9, AMER PHYSICAL SOC, 2002年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss issues in a scenario where hierarchical Yukawa couplings are generated through the strong dynamics of superconformal field theories (SCFTs). Independently of the mediation mechanism of supersymmetry breaking, the infrared convergence property of SCFTs can provide an interesting solution to the supersymmetric flavor problem; sfermion masses are suppressed around the decoupling scale of SCFTs and eventually become degenerate to some degree, thanks to family-independent radiative corrections governed by the gaugino masses of the minimal supersymmetric standard model (MSSM). We discuss under what conditions the degeneracy of the sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then explicitly study sfermion mass degeneracy within the framework of grand unified theories coupled to SCFTs. It is found that the degeneracy for right-handed sleptons becomes worse in the conventional SU(5) model than in the MSSM. On the other hand, in the flipped SU(5)xU(1) model, each right-handed lepton is still an SU(5) singlet, whereas the B-ino mass M-1 is determined by two independent gaugino masses of SU(5)xU(1). These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate on how further improvement can be obtained in the SCFT approach.

More about Kaluza-Klein regularization
T Kobayashi, H Terao
PROGRESS OF THEORETICAL PHYSICS, 107, 4, 785, 792, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 2002年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the so-called "'Kaluza-Klein regularization". We calculate one-loop corrections to the Higgs mass due to Kaluza-Klein modes explicitly in a model with SUSY breaking mass splitting between bosonic and fermionic modes. We perform the proper time cutoff at 1/Lambda(2) and the KK level truncation at l. It is shown that a finite result is obtained as long as l >> RLambda for the compactification radius R.

Yukawa hierarchy transfer from the superconformal sector and degenerate sfermion masses - art. no. 015004
T Kobayashi, H Nakano, H Terao
PHYSICAL REVIEW D, 65, 1, AMER PHYSICAL SOC, 2002年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a new type of supersymmetric model coupled to superconformal (SC) field theories, leading simultaneously to hierarchical Yukawa couplings and completely degenerate sfermion masses. We consider models with an extra Abelian gauge symmetry to generate hierarchical structure for couplings between the standard model (SM) sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of model, the flavor-independent structure of the superconformal fixed point guarantees that the sfermion masses of the first and the second generations are completely degenerate at low energy.

Yukawa hierarchy transfer from the superconformal sector and degenerate sfermion masses
Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao
Physical Review D, 65, 1, 2002年, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a new type of supersymmetric model coupled to superconformal (SC) field theories, leading simultaneously to hierarchical Yukawa couplings and completely degenerate sfermion masses. We consider models with an extra Abelian gauge symmetry to generate hierarchical structure for couplings between the standard model (SM) sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of model, the flavor-independent structure of the superconformal fixed point guarantees that the sfermion masses of the first and the second generations are completely degenerate at low energy. © 2001 The American Physical Society.

Sfermion masses in Nelson-Strassler-type models: Supersymmetric standard models coupled with superconformal field theories
T Kobayashi, H Terao
PHYSICAL REVIEW D, 64, 7, AMER PHYSICAL SOC, 2001年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study soft supersymmetric (SUSY) breaking parameters in the Nelson-Strassler-type models: SUSY standard models coupled with superconformal field theories (SCFT's). In this type of model, soft SUSY breaking parameters including sfermion masses can be suppressed around the decoupling scale of SCFT's. We clarify the condition to derive exponential suppression of sfermion masses within the framework of pure SCFT's. Such behavior is favorable for degeneracy of sfermion masses. However, the realistic sfermion masses are not quite degenerate due to the gauge couplings and the gaugino masses in the standard model sector. We show the sfermion mass spectrum obtained in such models. The aspect of suppression for the soft SUSY breaking parameters is also demonstrated in an explicit model. We also give a mechanism generating the mu term of the electroweak scale by a singlet field coupled with the SCFT.

Fermion mass hierarchies and small mixing angles from extra dimensions
M Bando, T Kobayashi, T Noguchi, K Yoshioka
PHYSICAL REVIEW D, 63, 11, AMERICAN PHYSICAL SOC, 2001年06月, ［査読有り］
英語, 研究論文（学術雑誌）, In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive the necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimensions. Several specific mechanisms to realize the conditions are presented. We also take into account the generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at a high-energy scale. A toy model is shown to lead to realistic quark mass matrices.

Direct detection of neutralino dark matter and the anomalons dipole moment of the muon
M Drees, YG Kim, T Kobayashi, MM Nojiri
PHYSICAL REVIEW D, 63, 11, AMERICAN PHYSICAL SOC, 2001年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We compare predictions for the spin-independent contribution to the neutralino-proton scattering cross section sigma (xp) and for the anomalous magnetic dipole moment of the muon, a(mu)= (g(mu) - 2)/2, in models with gravity-mediated supersymmetry breaking. We nearly always find a positive correlation between these two measurables; i.e., scenarios with larger a(mu) also tend to have larger sigma (xp), but the detailed prediction differs greatly between models. Tn particular, we find that for the popular MSUGRA scenario with universal soft breaking masses at the scale of grand unification, measurements of a(mu) currently seem more promising. On the other hand, if scalar soft breaking masses at the GUT scale receive sizable contributions from SO(10) D terms, one often finds scenarios with large sigma (xp) but a(mu) below the currently foreseen sensitivity. A string-inspired model with a nonuniversal scalar spectrum at the GUT scale falls between these two cases.

Restricted flavor structure of soft SUSY breaking trilinear couplings
T Kobayashi, O Vives
PHYSICS LETTERS B, 506, 3-4, 323, 330, ELSEVIER SCIENCE BV, 2001年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We analyze the flavor structure of the trilinear couplings in the different theoretical models of SUSY breaking. We generically obtain A(ij) = A(i)(L) + A(j)(R) in all the models examined. In fact, this is the rigorous form when SUSY breaking effects appear through the Kahler metric of chiral fields or through wave-function renormalization. Indeed, the low-energy phenomenological requirements from the absence of charge and color breaking minima and the measurements in flavor changing neutral current (FCNC) observables strongly favor this restricted form of the trilinear matrices. As a straightforward consequence the number of unknown parameters associated with the trilinear couplings is decreased in a factor of 2. (C) 2001 Elsevier Science B.V. All rights reserved.

Can we distinguish SUSY breaking terms between weakly and strongly coupled heterotic string theories?
T Kobayashi
PHYSICS LETTERS B, 506, 1-2, 187, 192, ELSEVIER SCIENCE BV, 2001年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study soft SUSY breaking terms in heterotic M-theory. We show that both weakly and strongly coupled heterotic string models lead to the same relations of soft SUSY breaking terms, A = -M and m(2) = M-2/3, up to O((alphaT/S)(2)). (C) 2001 Published by Elsevier Science B.V.

Exact finite unified theories
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 16, 11, 2053, 2057, WORLD SCIENTIFIC PUBL CO PTE LTD, 2001年04月, ［査読有り］
英語, 研究論文（学術雑誌）, Finite Unified Theories are N = 1 supersymmetric GUT's that can be made finite beyond the unification point, including the softly broken sector. The new characteristic predictions of FUTs are: 1) The lightest Higgs boson mass is predicted to be in the window 120-130 GeV, in case the LSP is neutralino, while in case the LSP is the <(<tau>)over bar> (which can be consistently accommodated in presence of bilinear R-parity violating terms) it can be as light as 111 GeV. 2) The s-spectrum starts above several hundreds of GeV.

Sfermion masses in Nelson-Strassler type of models
SUSY standard models coupled with SCFTs, 2001年, ［査読有り］

Sfermion masses in Nelson-Strassler-type models: Supersymmetric standard models coupled with superconformal field theories
Tatsuo Kobayashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 64, 7, 15, 2001年, ［査読有り］
英語, 研究論文（学術雑誌）, We study soft supersymmetric (SUSY) breaking parameters in the Nelson-Strassler-type models: SUSY standard models coupled with superconformal field theories (SCFT’s). In this type of model, soft SUSY breaking parameters including sfermion masses can be suppressed around the decoupling scale of SCFT’s. We clarify the condition to derive exponential suppression of sfermion masses within the framework of pure SCFT’s. Such behavior is favorable for degeneracy of sfermion masses. However, the realistic sfermion masses are not quite degenerate due to the gauge couplings and the gaugino masses in the standard model sector. We show the sfermion mass spectrum obtained in such models. The aspect of suppression for the soft SUSY breaking parameters is also demonstrated in an explicit model. We also give a mechanism generating the μ term of the electroweak scale by a singlet field coupled with the SCFT. © 2001 The American Physical Society.

Fermion mass hierarchies and small mixing angles from extra dimensions
Masako Bando, Tatsuo Kobayashi, Tatsuya Noguchi, Koichi Yoshioka
Physical Review D - Particles, Fields, Gravitation and Cosmology, 63, 11, 9, 2001年, ［査読有り］
英語, 研究論文（学術雑誌）, In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive the necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimensions. Several specific mechanisms to realize the conditions are presented. We also take into account the generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at a high-energy scale. A toy model is shown to lead to realistic quark mass matrices. © 2001 The American Physical Society.

Kaluza-Klein mediated supersymmetry breaking
T Kobayashi, K Yoshioka
PHYSICAL REVIEW LETTERS, 85, 26, 5527, 5530, AMER PHYSICAL SOC, 2000年12月, ［査読有り］
英語, 研究論文（学術雑誌）, The four-dimensional effective theories with compactified extra dimensions are considered. We then discuss a new framework for communicating supersymmetry breaking to the visible sector where the radius modulus, which determines the size of extra dimensions, has an auxiliary vacuum expectation value. The modulus couplings generate mass splitting in Kaluza-Klein supermultiplets and they act as messengers of supersymmetry breaking. The soft mas ses are expressed in terms of renormalization-group functions and the sparticle spectrum is determined by what kind of field propagates in the bulk.

Softly broken supersymmetric Gauge-Higgs-Yukawa theories as renormalizable composite models
T Kobayashi, H Terao
PHYSICS LETTERS B, 489, 1-2, 233, 242, ELSEVIER SCIENCE BV, 2000年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We examine the (softly broken) supersymmetric gauge-Higgs-Yukawa theories satisfying the compositeness conditions at a certain scale. In these theories the Higgs superfields can be regarded as the chiral composite fields. It is found that there are the fundamental theories, which contain the dimension 5 interactions and the hard SUSY breaking in perturbation, turn to be renormalizable and also softly broken theories in the nonperturbative framework. The soft SUSY breaking parameters as well as the Yukawa coupling in the corresponding gauge-Higgs-Yukawa theories are restricted by the renormalization group invariant relations. (C) 2000 Published by Elsevier Science B.V.

New RG-invariants of soft supersymmetry breaking parameters
T Kobayashi, K Yoshioka
PHYSICS LETTERS B, 486, 1-2, 223, 227, ELSEVIER SCIENCE BV, 2000年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study new renormalization-group invariant quantities of soft supersymmetry breaking parameters other than the ratio of gaugino mass to gauge coupling squared by using the spurion method. The obtained invariants are useful to probe supersymmetry breaking and mu-term generation mechanisms at high-energy scale. We also discuss the convergence behavior of fixed points of supersymmetry breaking parameters. (C) 2000 Elsevier Science B.V. All rights reserved.

Electroweak symmetry breaking and s-spectrum in M-theory
T Kobayashi, J Kubo, H Shimabukuro
NUCLEAR PHYSICS B, 580, 1-2, 3, 28, ELSEVIER SCIENCE BV, 2000年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study soft SUSY breaking parameters in M-theory with and without 5-brane moduli fields. We investigate successful electroweak symmetry breaking and the positivity of stau mass squared. A value of alpha(T + (T) over bar) is phenomenologically constrained. Also we have phenomenological constraints on magnitudes of derivatives of the Kahler potential for the 5-brane moduli field. We study mass spectra in the allowed regions. (C) 2000 Elsevier Science B.V. All rights reserved.

EDM-free supersymmetric CP violation with non-universal soft terms
S Khalil, T Kobayashi, O Vives
NUCLEAR PHYSICS B, 580, 1-2, 275, 288, ELSEVIER SCIENCE BV, 2000年07月, ［査読有り］
英語, 研究論文（学術雑誌）, Non-universality in the soft breaking terms is a common feature in most superstring inspired SUSY models. This property is required to obtain sizeable CP violation effects from SUSY and, on the other hand, can be used to avoid the electric dipole moment (EDM) constraints. We take advantage of these qualities and explore a class of SUSY models based on type I string theory where scalar masses, gaugino masses and trilinear couplings are non-universal. In this framework, we show that, in the presence of large SUSY phases, the bounds on the electric dipole moments can be controlled without fine-tuning. At the same time, we find that these phases, free from EDM constraints, lead to large contributions to the observed CP phenomena in Kaon system and, in particular, to direct CP violation in epsilon'/epsilon. (C) 2000 Elsevier Science B.V. All rights reserved.

Yukawa hierarchy from extra dimensions and infrared fixed points
M Bando, T Kobayashi, T Noguchi, K Yoshioka
PHYSICS LETTERS B, 480, 1-2, 187, 192, ELSEVIER SCIENCE BV, 2000年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We discuss the existence of hierarchy of Yukawa couplings in the models with extra spatial dimensions. The hierarchical structure is induced by the power behavior of the cutoff dependence of the evolution equations which yield large suppressions of couplings at the compactification scale. The values of coupling constants at this scale can be made stable almost independently of the initial input parameters by utilizing the infrared fixed point. We find that the Yukawa couplings converge to the fixed points very quickly because of the enhanced energy dependence of the suppression factor from extra dimensions as well as in the case of large gauge couplings at high-energy scale. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

On different criteria for confinement
M Chaichian, T Kobayashi
PHYSICS LETTERS B, 481, 1, 26, 32, ELSEVIER SCIENCE BV, 2000年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We compare two approaches in supersymmetric confinement, the Seiberg formulation and the superconvergence rule. For the latter, the critical point is gamma(00) = 0 in the Landau gauge We find 4 gamma(00) = beta(0) is the critical point for most of confining theories without a tree-level superpotential in the Seiberg formulation, in particular, in the large N-c and N-f limit. We show how confining theories with a discrete symmetry and a tree-level superpotential connect these two critical points: the large and small discrete symmetry limits correspond to the critical points 4 gamma(00) = beta(0) and gamma(00) = 0 respectively. (C) 2000 Elsevier Science B.V. All rights reserved.

RG-invariant Sum Rule in a Generalization of Anomaly-Mediated SUSY Breaking Models
2000年, ［査読有り］

Phenomenological constraints on SUSYSU(5) GUTs with non-universal gaugino masses
K Huitu, Y Kawamura, T Kobayashi, K Puolamaki
HIGH ENERGY PHYSICS 99, PROCEEDINGS, 786, 788, IOP PUBLISHING LTD, 2000年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, We study phenomenological aspects of supersymmetric SU(5) grand unified theories with non-universal gaugino masses. For large tan beta, we investigate constraints from the requirement of successful electroweak symmetry breaking, the positivity of stau mass squared and the b --> s gamma decay rate. We also calculate loop corrections to the bottom mass due to superpartners.

Infrared alignment of SUSY
2000年, ［査読有り］

Bottom-up approach to B-parameter in minimal supersymmetric standard model
Y Kawamura, T Kobayashi, M Watanabe
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 15, 1, 81, 103, WORLD SCIENTIFIC PUBL CO PTE LTD, 2000年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study mu and B-parameters in the minimal supersymmetric standard model (MSSM) based on the radiative electroweak symmetry breaking scenario using "bottom-up" approach and show how useful our approach is to select a phenomenologically viable model beyond the MSSM under the assumption that the underlying theory is a string model or a gauge-Yukawa unified gauge model.

Prediction of the Higgs mass from finite and minimal susy Gauge-Yukawa GUTs
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
HIGH ENERGY PHYSICS 99, PROCEEDINGS, 804, 806, IOP PUBLISHING LTD, 2000年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, The search for renormalization group invariant (RGI) relations among the couplings of GUTs holding beyond the unification point leads to the predictive scheme of Gauge-Yukawa Unified Theories. In this class of theories, of particular interest are those GUTs which are finite beyond the unification paint even to all orders in perturbation theory, i.e. exactly finite. Extending the search to the soft supersymmetry-breaking (SSB) sector of these theories we obtain exact RGI relations and exact finite theories also in this sector. Taking into account several phenomenological constraints we obtain an accurate prediction of the standard model (SM) Higgs mass in addition to the previous successful prediction of the top quark mass. Another interesting and distinct feature of these models is that their predictions for the spectrum beyond the SM starts above several hundreds of GeV.

Gauge coupling unification with extra dimensions and correction due to higher dimensional operators
K Huitu, T Kobayashi
PHYSICS LETTERS B, 470, 1-4, 90, 94, ELSEVIER SCIENCE BV, 1999年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the gauge coupling unification with extra dimensions. We Lake into account corrections due to the higher dimensional operators. We show the prediction of alpha(3)(M-Z) is sensitive to such corrections, even if c(Phi)/M = O(0.01). We also discuss the b - tau Yukawa unification. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Generic gravitational corrections to gauge couplings in SUSYSU(5) GUTs
K Huitu, Y Kawamura, T Kobayashi, K Puolamaki
PHYSICS LETTERS B, 468, 1-2, 111, 117, ELSEVIER SCIENCE BV, 1999年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We study non-universal corrections to the gauge couplings due to higher dimensional operators in supersymmetric SU(5) grand unified theories. The corrections are, in general, parametrized by three components originating from 24, 75 and 200 representations. We consider the prediction of alpha(3)(M-z) along each 24, 75 and 200 direction, and their linear combinations. The magnitude of GUT scale and its effects on proton decay are discussed. Non-SUSY case is also examined. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

F-term inflation in M-theory with five-branes
SM Harun-or-Rashid, T Kobayashi, H Shimabukuro
PHYSICS LETTERS B, 466, 2-4, 95, 99, ELSEVIER SCIENCE BV, 1999年11月, ［査読有り］
英語, 研究論文（学術雑誌）, We study F-term inflation in M-theory with and without five-brane moduli fields. We show the slow rolling condition is not satisfied in M-theory without five-brane moduli fields, but it can be satisfied in the case with non-vanishing F-terms of five-brane moduli fields. (C) 1999 Elsevier Science B.V. All rights reserved.

CP violation in a supersymmetric model with nondegenerate A terms
S Khalil, T Kobayashi, A Masiero
PHYSICAL REVIEW D, 60, 7, AMERICAN PHYSICAL SOC, 1999年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the CP phases of the soft supersymmetry breaking terms in string-inspired models with nonuniversal trilinear couplings. We show that such nonuniversality plays an important role on all CP violating processes. In particular these new supersymmetric sources of CP violation may significantly contribute to the observed CP phenomena in kaon physics while respecting the severe bound on the electric dipole moment of the neutron. [S0556-2821(99)03217-8].

Supersymmetric CP violation epsilon '/epsilon due to asymmetric A-matrix
S Khalil, T Kobayashi
PHYSICS LETTERS B, 460, 3-4, 341, 347, ELSEVIER SCIENCE BV, 1999年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We study contributions of supersymmetric CP phases to the CP violation epsilon'/epsilon in models with asymmetric A-matrices. We consider asymmetric A-matrices, which are obtained from string-inspired supergravity. We show that a certain type of asymmetry of A-matrices enhances supersymmetric contributions to the CP violation epsilon'/epsilon and the supersymmetric contribution to epsilon'/epsilon can be of order of the KTeV result, epsilon'/epsilon similar to 10(-3). (C) 1999 Elsevier Science B.V. All rights reserved.

Running of soft parameters in extra space-time dimensions
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
NUCLEAR PHYSICS B, 550, 1-2, 99, 122, ELSEVIER SCIENCE BV, 1999年06月, ［査読有り］
英語, 研究論文（学術雑誌）, The evolution of the parameters including those in the soft supersymmetry-breaking (SSB) sector is studied in the minimal supersymmetric standard model (MSSM) with a certain set of Kaluza-Klein towers which has been recently considered by Dienes et al. We use the continuous Wilson renormalization group technique to derive the one-loop matching condition between the effective, renormalizable and original, unrenormalizable theories. We investigate whether the assumption of a large compactification radius in the model is consistent with the gauge coupling unification, the b-tau unification and the radiative breaking of the electroweak gauge symmetry with the universal SSB terms. We calculate the superpartner spectrum under the assumption of the universal SSB parameters to find differences between the model and the MSSM. (C) 1999 Elsevier Science B.V. All rights reserved.

Exact finite and Gauge-Yukawa unified theories and their predictions
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
ACTA PHYSICA POLONICA B, 30, 6, 2013, 2027, JAGIELLONIAN UNIV PRESS, 1999年06月, ［査読有り］
英語, 研究論文（学術雑誌）, The recent developments in the soft supersymmetry breaking (SSB) sector of Gauge-Yukawa and Finite Unified Theories permit the derivation of exact renormalization group invariant results also in this sector of the theory. Of particular interest is a RGI sum rule for the soft scalar masses holding to all-orders in perturbation theory. In the case of Finite Unified Theories the sum rule ensures the all-loop finiteness also in their SSB sector and in this way are promoted to completely finite ones. Using the sum rule we investigate the minimal supersymmetric Gauge-Yukawa and two Finite-Gauge-Yukawa SU(5) models. The characteristic features of these models are: a) the old agreement of the top quark mass prediction remains unchanged, b) the lightest Higgs boson is predicted to be around 120 GeV; c) the s-spectrum starts above several hundreds of GeV.

Finite and Gauge-Yukawa Unified Theories: Theory and predictions
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
PARTICLES AND FIELDS, 490, 279, 309, AMER INST PHYSICS, 1999年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, All - loop Finite Unified Theories (FUTs) are very interesting N = 1 GUTs in which a complete reduction of couplings has been achieved. FUTs realise an old field theoretical dream and have remarkable predictive power. Reduction of dimensionless couplings in N = 1 GUTs is achieved by searching for renormalization group invariant (RGI) relations among them holding beyond the unification scale. Finiteness results from the fact that there exists RGI relations among dimensionless couplings that guarantee the vanishing of the beta - functions in certain N = 1 supersymmetric GUTS even to all orders. Recent developments in the soft supersymmetry breaking (SSB) sector of N = 1 GUTs and FUTs lead to exact RGI relations also in this sector of the theories. Of particular interest is a RGI sum rule for the sok scaler masses holding to all orders. The characteristic features of SU(5) models that have been constructed based on the above tools are: a) the old agreement of the top quark prediction with the measured value remains unchanged, b) the lightest Higgs boson is predicted to be around 120 GeV, c) the s - spectrum starts above several hundreds of GeV.

Vacuum structure of softly broken N = 1 supersymmetric QCD
M Chaichian, T Kobayashi
PHYSICS LETTERS B, 442, 1-4, 192, 198, ELSEVIER SCIENCE BV, 1998年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study softly broken N = 1 supersymmetric QCD with the gauge group SU(N-c) and N-f flavors of quark pairs. We investigate vacuum structure of the theory with generic soft supersymmetry breaking terms. Trilinear soft breaking terms play an essential role in determining vacua. For N-f = N-c + 1, chiral symmetry is broken for a sufficiently large magnitude of trilinear couplings, while it is unbroken in the case with only soft masses. In the case where appearance of trilinear coupling terms is allowed, i.e. for N-f greater than or equal to N-c + 1, we have two possible vacua, the trivial and non-trivial ones. Otherwise, we only have the non-trivial vacuum. which corresponds to the non-trivial vacuum in the N-f greater than or equal to N-c + 1 theory. (C) 1998 Elsevier Science B.V. All rights reserved.

Vacuum structure of softly broken N = 1 supersymmetric QCD
M Chaichian, T Kobayashi
PHYSICS LETTERS B, 442, 1-4, 192, 198, ELSEVIER SCIENCE BV, 1998年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study softly broken N = 1 supersymmetric QCD with the gauge group SU(N-c) and N-f flavors of quark pairs. We investigate vacuum structure of the theory with generic soft supersymmetry breaking terms. Trilinear soft breaking terms play an essential role in determining vacua. For N-f = N-c + 1, chiral symmetry is broken for a sufficiently large magnitude of trilinear couplings, while it is unbroken in the case with only soft masses. In the case where appearance of trilinear coupling terms is allowed, i.e. for N-f greater than or equal to N-c + 1, we have two possible vacua, the trivial and non-trivial ones. Otherwise, we only have the non-trivial vacuum. which corresponds to the non-trivial vacuum in the N-f greater than or equal to N-c + 1 theory. (C) 1998 Elsevier Science B.V. All rights reserved.

Infrared behaviour of softly broken SQCD and its dual
A Karch, T Kobayashi, J Kubo, G Zoupanos
PHYSICS LETTERS B, 441, 1-4, 235, 242, ELSEVIER SCIENCE BV, 1998年11月, ［査読有り］
英語, 研究論文（学術雑誌）, Applying the recently obtained results on the renormalization of soft supersymmetry-breaking parameters, we investigate the infrared behaviour of the softly broken supersymmetric QCD as well as its dual theory in the conformal window. Under general assumptions on beta-functions, it is shown that the soft supersymmetry-breaking parameters asymptotically vanish in the infrared limit so that superconformal symmetry in softly broken supersymmetric QCD and in its dual theory revives at the infrared fixed point, provided the soft scalar masses satisfy certain renormalization group invariant relations. If these relations are not satisfied, there exist marginal operators in both theories that lead to the breaking of supersymmetry and also colour symmetry. (C) 1998 Elsevier Science B.V. All rights reserved.

Constraints on supersymmetric SO(10) GUTs with sum rules among soft masses
Y Kawamura, T Kobayashi, H Shimabukuro
PHYSICS LETTERS B, 436, 1-2, 108, 116, ELSEVIER SCIENCE BV, 1998年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study phenomenological aspects of supersymmetric SO(10) GUTs with sum rules among soft SUSY breaking parameters, In particular, the sum rule related to the stau mass leads to the constraints from the requirements of successful electroweak breaking and the positivity of stau mass squared. The bottom quark mass is also estimated. (C) 1998 Elsevier Science B.V. All rights reserved.

Yukawa unification in moduli-dominant SUSY breaking
S Khalil, T Kobayashi
NUCLEAR PHYSICS B, 526, 1-3, 99, 114, ELSEVIER SCIENCE BV, 1998年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We study Yukawa unification in string models with moduli-dominant SUSY breaking. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Such non-universality is important for phenomenological aspects of Yukawa unification, i.e., successful electroweak breaking, SUSY corrections to the bottom mass and the branching ratio of b --> s gamma, We show three regions in the whole parameter space that lead to successful electroweak breaking and allow small SUSY corrections to the bottom mass. For these three regions we investigate the b --> s gamma decay and mass spectra, (C) 1998 Elsevier Science B.V.

Sum rules in the superpartner spectrum of the minimal supersymmetric standard model
Y Kawamura, T Kobayashi, J Kubo
PHYSICS LETTERS B, 432, 1-2, 108, 113, ELSEVIER SCIENCE BV, 1998年07月, ［査読有り］
英語, 研究論文（学術雑誌）, Assuming that the universal sum rules for soft supersymmetry-breaking terms, which have been recently found both in four-dimensional superstring models and in supersymmertic gauge-Yukawa unified gauge models, are satisfied above and at the grand unification scale, we investigate their low energy consequences and derive sum rules in the superpartner spectrum of the minimal supersymmetric standard model (MSSM). These sum rules contain only observable parameters of the MSSM, and could be experimentally verified in future. (C) 1998 Elsevier Science B.V. All rights reserved.

Quark mass matrices in superstring models
T Kobayashi, ZZ Xing
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 13, 13, 2201, 2215, WORLD SCIENTIFIC PUBL CO PTE LTD, 1998年05月, ［査読有り］
英語, 研究論文（学術雑誌）, Four simple but realistic patterns of quark mass matrices are derived from orbifold models of superstring theory in the absence of gauge symmetries. Two of them correspond to the Ramond-Roberts-Ross types, which have five texture zeros in up and down quark sectors. The other two, with four texture zeros, preserve the structural parallelism between up and down sectors. The phenomenological consequences of these mass matrices on flavor mixings and CP violation are analyzed at the weak scale. With the same input values of quark mass ratios, we find that only one or two of the four patterns can be in good agreement with current experimental data.

Further all-loop results in softly-broken supersymmetric gauge theories
T Kobayashi, J Kubo, G Zoupanos
PHYSICS LETTERS B, 427, 3-4, 291, 299, ELSEVIER SCIENCE BV, 1998年05月, ［査読有り］
英語, 研究論文（学術雑誌）, It is proven that the recently found, renormalization-group invariant sum rule for the soft scalar masses in softly-broken N=l supersymmetric gauge-Yukawa unified theories can be extended to all orders in perturbation theory. Ln the case of finite unified theories, the sum rule ensures the all-loop finiteness in the soft supersymmetry breaking sector. As a byproduct the exact beta function for the soft scalar masses in the Novikov-Shifman-Vainstein-Zakharov (NSVZ) scheme for softly-broken supersymmetric QCD is obtained. It is also found that the singularity appearing in the sum rule in the NSVZ scheme exactly coincides with that which has been previously found in a certain class of superstring models in which the massive string states are organized into N=4 supermultiplets. (C) 1998 Elsevier Science B.V. All rights reserved.

Probing mu-term generation mechanism in string models
Y Kawamura, T Kobayashi, M Watanabe
PHYSICS LETTERS B, 419, 1-4, 157, 166, ELSEVIER SCIENCE BV, 1998年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We give a generic method to select a realistic mu-term generation mechanism based on the radiative electroweak symmetry breaking scenario and study which type is hopeful within the framework of string theory. We discuss effects of the moduli F-term condensation and D-term contribution to soft scalar masses. (C) 1998 Elsevier Science B.V.

Constraints on finite soft supersymmetry-breaking terms
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
NUCLEAR PHYSICS B, 511, 1-2, 45, 68, ELSEVIER SCIENCE BV, 1998年02月, ［査読有り］
英語, Requiring the soft supersymmetry-breaking (SSB) parameters in finite gauge-Yukawa unified models to be finite up to and including two-loop order, we derive a two-loop sum rule for the soft scalar masses, It is shown that this sum rule coincides with that of a certain class of string models in which the massive string states are organized into N = 4 supermultiplets. We investigate the SSB sector of two finite SU(5) models. Using the sum rule which allows non-universality of the SSB terms and requiring that the lightest superparticle is neutral, we constrain the parameter space of the SSB sector in each model. (C) 1998 Elsevier Science B.V.

Reduction of couplings in supersymmetric GUTs　　　　　　　　　　　　　　　
J. Kubo, T. Kobayashi, M. Mondragon, G. Zoupanos
Proceedings of Science, 1, Sissa Medialab Srl, 1998年
英語, 研究論文（国際会議プロシーディングス）, Applications of the principle of reduction of couplings to the standard model and supersymmetric grand unified theories are reviewed. Phenomenological applications of renormalization group invariant sum rules for soft supersymmetry-breaking parameters are also discussed.

Gauge-Yukawa-finite unified theories and their predictions
T Kobayashi, J Kubo, M Mondragon, G Zoupanos
BEYOND THE STANDARD MODEL, 464, 471, WORLD SCIENTIFIC PUBL CO PTE LTD, 1998年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）, Gauge-Yukawa unified theories, and in particular those which are finite beyond the unification scale, have been extended to include a soft supersymmetry breaking (SSB) sector. In the case of the Finite Unified Theories a new solution to the condition of two-loop finiteness of the SSB parameters is found, which requires a sum rule for the relevant scalar masses. The sum rule permits violations of the universality of the scalar masses which is found to lead to phenomenological problems. The minimal supersymmetric SU(5) Gauge-Yukawa model and two Finite-Gauge-Yukawa models have been examined using the sum rule. The characteristic features of these models are: a) the old agreement of the top quark mass prediction persists using the new data, b) the lightest Higgs boson is predicted to be around 120 GeV, c) the s-spectrum starts above 200 GeV.

Notes on Curtright-Zachos deformations of osp(1,2) and super Virasoro algebras
N Aizawa, T Kobayashi, HT Sato
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 12, 32, 5867, 5883, WORLD SCIENTIFIC PUBL CO PTE LTD, 1997年12月, ［査読有り］
英語, 研究論文（学術雑誌）, Based on the quantum superspace construction of q-deformed algebra, we discuss a supersymmetric extension of the deformed Virasoro algebra, which is a subset of the q-W-infinity algebra which recently appeared in the context of two-dimensional string theory. We analyze two types of deformed super Virasoro algebra as well as their osp(1,2) subalgebras. Applying our quantum superspace structure to conformal field theory, we find the same type of deformation of affine sl(2) algebra.

Generic formula of soft scalar masses in string models
Y Kawamura, T Kobayashi
PHYSICAL REVIEW D, 56, 7, 3844, 3859, AMER PHYSICAL SOC, 1997年10月, ［査読有り］
英語, We derive a formula of soft supersymmetry-breaking scalar masses from four-dimensional string models within a more generic framework. We consider the effects of extra gauge symmetry breaking including an anomalous U(1) breaking through flat directions, that is, D-term and F-term contributions, particle mixing effects, and heavy-light mass mixing effects. Some phenomenological implications are discussed based on our mass formula.

Phenomenological implications of moduli-dominant SUSY breaking
Y Kawamura, S Khalil, T Kobayashi
NUCLEAR PHYSICS B, 502, 1-2, 37, 58, ELSEVIER SCIENCE BV, 1997年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study moduli-dominated SUSY breaking within the framework of string models. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Further gauginos are Lighter than sfermions. This non-universality has phenomenologically important implications. We investigate radiative electroweak symmetry breaking in the mass spectrum derived from moduli-dominated SUSY breaking, where the lightest chargino and neutralino are almost gauginos. Moreover, constraints from the branching ratio of b --> s gamma and the relic abundance of the LSP are also considered. The mass spectrum of moduli-dominated SUSY breaking is favorable to the experimental bound of the b --> s gamma decay decreasing its branching ratio. We obtain an upper bound for the gravitino mass from the cosmological constraint. (C) 1997 Elsevier Science B.V.

Soft scalar-mass sum rule in gauge-Yukawa unified models and its superstring interpretation
Y Kawamura, T Kobayashi, J Kubo
PHYSICS LETTERS B, 405, 1-2, 64, 70, ELSEVIER SCIENCE BV, 1997年07月, ［査読有り］
英語, 研究論文（学術雑誌）, It is shown that a certain sum rule for soft supersymmetry-breaking scalar masses, which has been recently found in a certain class of superstring models, is universal for gauge-Yukawa unified models. To explain this coincidence, we argue that the low-energy remnant of the target-space duality invariance in the effective supergravity of compactified superstrings can be identified with the (broken) scale invariance in gauge-Yukawa unified models, and that gauge-Yukawa unification which is indispensable for the sum rule to be satisfied follows from the matching of anomalies. (C) 1997 Published by Elsevier Science B.V.

''Anomalous'' U(1) symmetry in orbifold string models
T Kobayashi, H Nakano
NUCLEAR PHYSICS B, 496, 1-2, 103, 131, ELSEVIER SCIENCE BV, 1997年07月, ［査読有り］
英語, 研究論文（学術雑誌）, ''Anomalous'' U(1) gauge symmetry with a Green-Schwarz anomaly cancellation mechanism is discussed in the orbifold construction of four-dimensional heterotic string models. Some conditions are given as criteria to have ''anomalous'' U(1) in orbifold string models. In particular, ''anomalous'' U(1) is absent if the massless twisted matter has no mixing between visible and hidden sectors or if a certain type of discrete symmetries are found. We then give a general procedure for classifying orbifold models with ''anomalous'' U(1) and for identifying the ''anomalous'' U(1) basis. We illustrate our procedure in Z(3) and Z(4) orbifold models. According to our procedure, the classification of ''anomalous'' U(1) can be reduced to classification in the absence of a Wilson line. We also discuss discrete symmetries left unbroken after the ''anomalous'' U(1) breaking. This includes a possible relation between ''anomalous'' U(1) and discrete R symmetries. (C) 1997 Elsevier Science B.V.

Specific scalar mass relations in SU(3)xSu(2)xU(1)
Y Kawamura, T Kobayashi, T Komatsu
PHYSICS LETTERS B, 400, 3-4, 284, 294, ELSEVIER SCIENCE BV, 1997年05月, ［査読有り］
英語, 研究論文（学術雑誌）, We study flat directions and soft scalar masses using a Z(3) orbifold model with SU(3) x SU(2) x U(1) gauge group and extra gauge symmetries including an anomalous U(1) symmetry. Soft scalar masses contain D-term contributions and particle mixing effects after symmetry breaking and they are parametrized by a few parameters. Some specific relations among scalar masses are obtained. (C) 1997 Elsevier Science B.V.

A string-inspired ansatz for quark masses and mixing
T Kobayashi, ZZ Xing
MODERN PHYSICS LETTERS A, 12, 8, 561, 571, WORLD SCIENTIFIC PUBL CO PTE LTD, 1997年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We propose a simple but realistic pattern of quark mass matrices at the string scale, which can be derived from orbifold models of superstring theory with no use of gauge symmetries. This pattern is left-right symmetric and preserves the structural parallelism between up and down quark sectors. Its phenomenological consequences on flavor mixing and CP-violation are confronted with current experiments at the weak scale by using the renormalization group equations in the framework of minimal supersymmetric standard model. We find that good agreement is achievable without fine-tuning.

Generic formula of soft scalar masses in string models
Yoshiharu Kawamura, Tatsuo Kobayashi
Physical Review D - Particles, Fields, Gravitation and Cosmology, 56, 7, 3844, 3859, 1997年, ［査読有り］
英語, 研究論文（学術雑誌）, We derive a formula of soft supersymmetry-breaking scalar masses from four-dimensional string models within a more generic framework. We consider the effects of extra gauge symmetry breaking including an anomalous U(1) breaking through flat directions, that is, [Formula presented]-term and [Formula presented]-term contributions, particle mixing effects, and heavy-light mass mixing effects. Some phenomenological implications are discussed based on our mass formula. © 1997 The American Physical Society.

Flat directions in Z(2n) orbifold models
Y Kawamura, T Kobayashi
NUCLEAR PHYSICS B, 481, 3, 539, 576, ELSEVIER SCIENCE BV, 1996年12月, ［査読有り］
英語, 研究論文（学術雑誌）, We study generic features related to matter contents and flat directions in Z(2n) orbifold models. It is shown that Z(2n) orbifold models have massless conjugate pairs, R and (R) over bar, in certain twisted sectors as well as one of untwisted subsectors. Using these twisted sectors, Z(2n) orbifold models are classified into two types. Conjugate pairs, R and (R) over bar,lead to D-flatness as [R] = [ (R) over bar] not equal 0. We investigate generic superpotentials derived from orbifold models so as to show that this direction is indeed a flat direction.

Soft scalar masses in string models with anomalous U(1) symmetry (vol 375, pg 141, 1996)
Y Kawamura, T Kobayashi
PHYSICS LETTERS B, 388, 4, 867, 868, ELSEVIER SCIENCE BV, 1996年11月, ［査読有り］
英語

Remarks on the Kielanowski parametrization of the Kobayashi-Maskawa matrix
T Kobayashi, ZZ Xing
MODERN PHYSICS LETTERS A, 11, 31, 2531, 2537, WORLD SCIENTIFIC PUBL CO PTE LTD, 1996年10月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the Kielanowski parametrization of the Kobayashi-Maskawa (KM) matrix V. A new two-angle parametrization is investigated explicitly and compared with the Kielanowski ansatz. Both of them are symmetric matrices and lead to \V-13/V-23\ = 0.129. Necessary corrections to the off-diagonal symmetry of Si are also discussed.

Quasi Yukawa fixed point due to decoupling of SUSY particles
T Kobayashi, Y Yamagishi
PHYSICS LETTERS B, 381, 1-3, 169, 176, ELSEVIER SCIENCE BV, 1996年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study effects of SUSY particle decouplings on a quasi fixed point (QFP) of Yukawa coupling. From renormalization group analysis it is shown that if the SUSY breaking scale M(S) is large (greater than or similar to 1 TeV), effects of decoupling of Higgsinos and squarks raise the top Yukawa QFP. Tnis tendency is enhanced in most cases of non-universal SUSY breaking. For the case of M(S) less than or similar to 1 TeV, the decoupling of gluinos lowers m(t)(QFP). We checked some parameter dependencies for the top Yukawa QFP. The bottom-top Yukawa unified case is also studied. When top quark mass is measured more precisely, some patterns of soft mass spectra could be excluded if a rather large initial top Yukawa coupling is realized by the underlying theory.

Quantum deformation of igl(n) algebra on quantum space
T Kobayashi, HT Sato
MODERN PHYSICS LETTERS A, 11, 7, 535, 543, WORLD SCIENTIFIC PUBL CO PTE LTD, 1996年03月, ［査読有り］
英語, 研究論文（学術雑誌）, We study quantum deformed gl(n) and igl(n) algebras on a quantum space discussing multi-parametric extension. We realize elements of deformed gl(n) and igl(n) algebras by a quantum fermionic space. We investigate a map between deformed igl(2) algebras of our basis and other basis.

Implications of nonuniversal soft masses for gauge coupling unification
R Altendorfer, T Kobayashi
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 11, 5, 903, 920, WORLD SCIENTIFIC PUBL CO PTE LTD, 1996年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the gauge coupling unification of the minimal supersymmetric standard model with nonuniversal soft scalar and gaugino masses. The unification scale of the gauge couplings is estimated for nonuniversal cases. It is sensitive to the nonuniversality. It turns out that these cases can be combined with the assumption of string unification, which leads to a prediction of sin(2) theta(W)(M(Z)) and k(1), the normalization of the U(1)(Y) generator. String unification predicts that k(1) = 1.3-1.4. These values have nontrivial implications for string model building. Two-loop corrections are also calculated. Some of these cases exhibit a large discrepancy between experiment and string unification. We calculate string threshold corrections to explain the discrepancy.

QUARK MASS MATRICES IN ORBIFOLD MODELS
T KOBAYASHI
PHYSICS LETTERS B, 358, 3-4, 253, 258, ELSEVIER SCIENCE BV, 1995年09月, ［査読有り］
英語, 研究論文（学術雑誌）, We study left-right symmetric quark mass matrices whose up- and down-sectors have the same structure. This type of realistic mass matrices are derived from orbifold models.

NEUTRON ELECTRIC-DIPOLE MOMENT UNDER NONUNIVERSAL SOFT SUSY BREAKING TERMS
T KOBAYASHI, M KONMURA, D SUEMATSU, K YAMADA, Y YAMAGISHI
PROGRESS OF THEORETICAL PHYSICS, 94, 3, 417, 433, KYOTO UNIV, 1995年09月, ［査読有り］
英語, 研究論文（学術雑誌）, The electric dipole moment of the neutron (EDMN) is re-examined in the framework of non-universal soft supersymmetry breaking. We review some features of the relation between the EDMN and non-universal soft supersymmetry breaking terms. It is shown that the constraints on the soft scalar masses and soft CP phases have a rather strong dependence on the non-universality of soft breaking terms. We also show that the soft CP phase phi(B) which has no natural suppression mechanism may not contribute significantly to the EDMN in a certain parameter region where the radiative symmetry breaking occurs successfully. If this is the case, phi(B) may not need to be so small.

SELECTION-RULES FOR NONRENORMALIZABLE COUPLINGS IN SUPERSTRING THEORIES
T KOBAYASHI
PHYSICS LETTERS B, 354, 3-4, 264, 270, ELSEVIER SCIENCE BV, 1995年07月, ［査読有り］
英語, 研究論文（学術雑誌）, We study nonrenormalizable coupling terms in Z(N) orbifold models. Nontrivial selection rules of couplings are provided and cannot be understood in terms of a simple symmetry of effective field theories. We also discuss phenomenological implications of theses selection rules for the quark mass matrices.

NONUNIVERSAL SOFT SCALAR MASSES IN SUPERSTRING THEORIES
T KOBAYASHI, D SUEMATSU, K YAMADA, Y YAMAGISHI
PHYSICS LETTERS B, 348, 3-4, 402, 410, ELSEVIER SCIENCE BV, 1995年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study soft scalar masses in comparison with gaugino masses in 4-dimensional string models. In general non-universal soft masses are derived in orbifold models. We give conditions on modular weights which lead to a large non-degeneracy in the soft scalar mass spectrum. This non-universality is applied to the unification of gauge coupling constants in the minimal string model.

MINIMAL STRING UNIFICATION AND YUKAWA COUPLINGS IN ORBIFOLD MODELS
T KOBAYASHI
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 10, 10, 1393, 1411, WORLD SCIENTIFIC PUBL CO PTE LTD, 1995年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the minimal supersymmetric standard model derived from Z(N) x Z(M) orbifold models. Moduli-dependent threshold corrections of gauge couplings are investigated to explain the measured values of the coupling constants. We also study the Yukawa couplings of the models. We find that the Z(2) x Z'(6), Z(2) x Z(6), Z(3) x Z(6) and Z(6) x Z(6) orbifold models have the possibility of deriving Yukawa couplings for the second and third generations as well as the measured gauge coupling constants. Allowed models are shown explicitly by combinations of modular weights for the matter fields.

MINIMAL STRING UNIFICATION AND CONSTRAINT ON HIDDEN SECTOR
H KAWABE, T KOBAYASHI, N OHTSUBO
NUCLEAR PHYSICS B, 434, 1-2, 210, 230, ELSEVIER SCIENCE BV, 1995年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We examine whether a minimal string model possessing the same massless spectra as the MSSM can be obtained from Z(4), Z(6) and Z(8) orbifold constructions. Using an anomaly cancellation condition of the target space duality symmetry, we derive allowable values of a level k(1) of U(1)(Y) for the minimal string model on the orbifolds through computer analyses. We investigate threshold corrections of the gauge coupling constants of SU(3), SU(2) and U(1)Y and examine consistencies of the model with the LEP experiments. It is found that Z(4) and Z(8)-II cannot derive the minimal string model but Z(6)-I, Z(6)-II and Z(8)-I are possible to derive it with k(1) = 29/21, 1 less than or equal to k(1) less than or equal to 32/21 and 1 less than or equal to k(1) less than or equal to 41/21, respectively, We obtain explicitly allowed combinations of modular weights. The minimum values of the moduli on unrotated planes are estimated within the ranges of the levels. Further we investigate what kinds of hidden sectors are consistent with the minimal string models. Also their gauge coupling constants of the hidden groups are estimated, We discuss Yukawa couplings of the models.

CP IN ORBIFOLD MODELS
T KOBAYASHI, CS LIM
PHYSICS LETTERS B, 343, 1-4, 122, 127, ELSEVIER SCIENCE BV, 1995年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study CP in orbifold models. It is found that the orbifolds always have some automorphisms as CP symmetry. The symmetries are restricted non-trivially due to geometrical structure of the orbifolds. Explicit analysis on Yukawa couplings also shows that CP is not violated in orbifold models.

GAUGE COUPLING UNIFICATION DUE TO NONUNIVERSAL SOFT SUPERSYMMETRY BREAKING
T KOBAYASHI, D SUEMATSU, Y YAMAGISHI
PHYSICS LETTERS B, 329, 1, 27, 32, ELSEVIER SCIENCE BV, 1994年06月, ［査読有り］
英語, 研究論文（学術雑誌）, Gauge coupling unification is studied in the MSSM with non-universal soft supersymmetry breaking terms. If gaugino masses are sufficiently smaller than scalar soft masses and the scalar soft masses have also certain types of non-universality, the gauge coupling unification scale can be larger than 3 x 10(16) GeV even within the MSSM contents. String unification may not need a large threshold correction or a large modulus value. We also discuss the relation to the string model building.

LEVELS OF U(1)Y IN MINIMAL STRING MODEL ON Z(N)XZ(M) ORBIFOLDS
H KAWABE, T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 325, 1-2, 77, 84, ELSEVIER SCIENCE BV, 1994年04月, ［査読有り］
英語, 研究論文（学術雑誌）, We study a minimal string model possessing the same massless spectra as the MSSM on Z(N) x Z(M) orbifolds. Threshold corrections of the gauge coupling constants of SU(3), SU(2) and U(1)Y are investigated in a case of an overall modulus. Using computer analyses, we search ranges of levels of U(1)Y allowed by the LEP experiments. It is found that Z3 x Z3 can not derive the minimal string model for a M(Z) SUSY breaking scale. The minimum values of the overall moduli are estimated within the ranges of the levels.

STUDY OF MINIMAL STRING UNIFICATION IN Z8 ORBIFOLD MODELS
H KAWABE, T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 322, 4, 331, 339, ELSEVIER SCIENCE BV, 1994年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the construction of the minimal supersymmetric standard model from the Z8 orbifold models. We use a target-space duality anomaly cancellation and a unification of gauge couplings as constraints. It is shown that some models obtained through a systematical search realize the unification of SU(3) and SU(2) coupling constants.

STUDY OF MINIMAL STRING UNIFICATION IN Z8 ORBIFOLD MODELS
H KAWABE, T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 322, 4, 331, 339, ELSEVIER SCIENCE BV, 1994年02月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the construction of the minimal supersymmetric standard model from the Z8 orbifold models. We use a target-space duality anomaly cancellation and a unification of gauge couplings as constraints. It is shown that some models obtained through a systematical search realize the unification of SU(3) and SU(2) coupling constants.

GEOMETRICAL ASPECTS OF Z(N) ORBIFOLD PHENOMENOLOGY
T KOBAYASHI, N OHTSUBO
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 9, 1, 87, 125, WORLD SCIENTIFIC PUBL CO PTE LTD, 1994年01月, ［査読有り］
英語, 研究論文（学術雑誌）, We study the geometrical and phenomenological aspects of Z(N) orbifold models. Conditions on-the background moduli and Wilson lines are clarified. We investigate the explicit Z(N)-invariant states through a modified GSO projection and calculate Yukawa coupling conditions due to space-group and SO(10) invariance. We estimate a contribution of a holomorphic instanton to the couplings.

Di#11;erential Calculi on h-deformed Bosonic and Fermionic Quantum Planes
1994年, ［査読有り］

THE Z(4)XZ(4) ORBIFOLD MODEL AT AN ENHANCEMENT POINT AND THE 2(6) MODEL
T KOBAYASHI, N OHTSUBO, K TANIOKA
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 8, 20, 3553, 3563, WORLD SCIENTIFIC PUBL CO PTE LTD, 1993年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We construct a ''shifted'' Z4 x Z4 orbifold model equivalent to a twisted Z4 X Z4 orbifold model at an enhancement point. It is proved that the N = 2 algebra of the 2(6) model is coincident with that of the ''shifted'' orbifold model. The correspondence between the Z4 x Z4 orbifold model and the 2(6) model is investigated with respect to massless spectra and Yukawa couplings. Also studied are Yukawa couplings and some other aspects of the models away from the enhancement point.

Q-DEFORMED CONFORMAL AND POINCARE ALGEBRAS ON QUANTUM 4-SPINORS
T KOBAYASHI, T UEMATSU
ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS, 58, 4, 559, 565, SPRINGER VERLAG, 1993年06月, ［査読有り］
英語, 研究論文（学術雑誌）, We investigate quantum deformation of conformal algebras by constructing the quantum space for sl(q)(4). The differential calculus on the quantum space and the action of the quantum generators are studied. We derive deformed su(2, 2) algebra from the deformed sl(4) algebra using the quantum 4-spinor and its conjugate spinor. The quantum 6-vector in so(q)(4, 2) is constructed as a tensor product of two sets of 4-spinors. We obtain the q-deformed conformal algebra with the suitable assignment of the generators which satisfy the reality condition. The deformed Poincare algebra is derived through a contraction procedure.

Q-DEFORMED SUPERCONFORMAL ALGEBRA ON QUANTUM SUPERSPACE
T KOBAYASHI, T UEMATSU
PHYSICS LETTERS B, 306, 1-2, 27, 33, ELSEVIER SCIENCE BV, 1993年05月, ［査読有り］
英語, 研究論文（学術雑誌）, A quantum deformation of four-dimensional superconformal algebra realized on quantum superspace is investigated. We study the differential calculus and the action of the quantum generators corresponding to sl(q)(1\4) which act on the quantum superspace. We derive deformed su(1\2, 2) algebras from the deformed sl(1\4) algebra. Through a contraction procedure we obtain a deformed super-Poincare algebra.

Q-DEFORMED SUPERCONFORMAL ALGEBRA ON QUANTUM SUPERSPACE
T KOBAYASHI, T UEMATSU
PHYSICS LETTERS B, 306, 1-2, 27, 33, ELSEVIER SCIENCE BV, 1993年05月, ［査読有り］
英語, 研究論文（学術雑誌）, A quantum deformation of four-dimensional superconformal algebra realized on quantum superspace is investigated. We study the differential calculus and the action of the quantum generators corresponding to sl(q)(1\4) which act on the quantum superspace. We derive deformed su(1\2, 2) algebras from the deformed sl(1\4) algebra. Through a contraction procedure we obtain a deformed super-Poincare algebra.

SHIFTED Z6 ORBIFOLD MODEL AND 1.4 MODEL
H KAWABE, T KOBAYASHI, N OHTSUBO
PROGRESS OF THEORETICAL PHYSICS, 88, 2, 431, 442, KYOTO UNIV, 1992年08月, ［査読有り］
英語, 研究論文（学術雑誌）, We explicitly construct a two-dimensional 'shifted' Z6 orbifold model equivalent to a two-dimensional twisted Z6 orbifold model at an enhancement point. Then we study equivalence of the shifted Z6 super-orbifold model and the 1.4 model. As applications to the (2,2) heterotic string theories, we investigate correspondence of the Z6 X Z6 (Z3 X Z6) orbifold model and (1.4)3 (1(3)(1.4)2) model.

CORRESPONDENCE OF Z4XZ4 ORBIFOLD MODEL AND 2(6) MODEL
T KOBAYASHI
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 110, 277, 290, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 1992年, ［査読有り］
英語, 研究論文（学術雑誌）, We construct a 'shifted' Z4 x Z4 orbifold model equivalent to a twisted Z4 x Z4 orbifold model at an enhancement point. It is proved that an N=2 superconformal algebra of a 2(2) theory coincides with that of the 2-dim 'shifted' Z4 orbifold model. We relate chiral primary states of the 2(6) model to 'shifted' ground states of the Z4 x Z4 orbifold model. Yukawa couplings are also studied.

ALLOWED YUKAWA COUPLINGS OF ZNXZM ORBIFOLD MODELS
T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 262, 4, 425, 431, ELSEVIER SCIENCE BV, 1991年06月, ［査読有り］
英語, 研究論文（学術雑誌）, SO(10) momenta and fixed points are studied for obtaining non-vanishing Yukawa couplings of Z(N) x Z(M) orbifold models. As an example, we investigate explicity three-point couplings of Z4 x Z4 and Z3 x Z3 orbifolds with the standard embedding and no discrete torsion. Comparing with the 2(6) and 1(9) model by Gepner's coset construction, respectively, we find discrepancies with respect to the numbers of (27) (27) (27) couplings, while the numbers of 27 are identical.

YUKAWA COUPLING CONDITION OF ZN ORBIFOLD MODELS
T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 245, 3-4, 441, 446, ELSEVIER SCIENCE BV, 1990年08月, ［査読有り］
英語, 研究論文（学術雑誌）

YUKAWA COUPLING CONDITION OF ZN ORBIFOLD MODELS
T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 245, 3-4, 441, 446, ELSEVIER SCIENCE BV, 1990年08月, ［査読有り］
英語, 研究論文（学術雑誌）

Z8 AND Z12 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, Y ONO, K TANIOKA
PHYSICS LETTERS B, 227, 3-4, 381, 386, ELSEVIER SCIENCE BV, 1989年08月, ［査読有り］
英語, 研究論文（学術雑誌）

Z8 AND Z12 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, Y ONO, K TANIOKA
PHYSICS LETTERS B, 227, 3-4, 381, 386, ELSEVIER SCIENCE BV, 1989年08月, ［査読有り］
英語, 研究論文（学術雑誌）

GAUGE GROUPS OF ZN ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, K TANIOKA
PROGRESS OF THEORETICAL PHYSICS, 82, 1, 171, 182, KYOTO UNIV, 1989年07月, ［査読有り］
英語, 研究論文（学術雑誌）

Z7 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO
PHYSICS LETTERS B, 212, 3, 339, 342, ELSEVIER SCIENCE BV, 1988年09月, ［査読有り］
英語, 研究論文（学術雑誌）

Remark on modular weights in low-energy effective field theory from type II string theory
Shota Kikuchi, Tatsuo Kobayashi, Kaito Nasu, Hajime Otsuka, Shohei Takada, Hikaru Uchida, Journal of High Energy Physics, 2023, 4, 2023年01月24日
We revisit the modular weights in type IIB magnetized D-brane models. The
simple analysis of wave function shows that the four-dimensional matter fields
have the modular weight -1/2, but it may shift as one in type IIA intersecting
D-brane models. For example, the localized gauge flux as well as the localized
curvature can shift the modular weight in the magnetized D-brane models. Such
corrections do not affect physical couplings such as physical Yukawa couplings.
However, it leads to differences in supersymmetry breaking sfermion masses,
which depend on the modular weights, although the $A$-term coefficients and the
sum of sfermion masses squared seem to be the same between two models.

Quark hierarchical structures in modular symmetric flavor models at level 6
Shota Kikuchi, Tatsuo Kobayashi, Kaito Nasu, Shohei Takada, Hikaru Uchida, 2023年01月10日
We study modular symmetric quark flavor models without fine-tuning. Mass
matrices are written in terms of modular forms, and modular forms in the
vicinity of the modular fixed points become hierarchical depending on their
residual charges. Thus modular symmetric flavor models in the vicinity of the
modular fixed points have a possibility to describe mass hierarchies without
fine-tuning. Since describing quark hierarchies without fine-tuning requires
$Z_n$ residual symmetry with $n\geq 6$, we focus on $\Gamma_6$ modular symmetry
in the vicinity of the cusp $\tau=i\infty$ where $Z_6$ residual symmetry
remains. We use only modular forms belonging to singlet representations of
$\Gamma_6$ to make our analysis simple. Consequently, viable quark flavor
models are obtained without fine-tuning.

Quark and lepton flavor structure in magnetized orbifold models at residual modular symmetric points
Kouki Hoshiya, Shota Kikuchi, Tatsuo Kobayashi, Hikaru Uchida, 2022年09月15日
We study quark and lepton mass matrices derived from magnetized
$T^2/\mathbb{Z}_2$ orbifold models. Quark and lepton masses have a large
hierarchy. In addition, mixing angles are large in the lepton sector, while
those are small in the quark sector. We find that this structure can be
realized in certain flavor models, which are identified by the zero points of
the zero-mode wave functions of fermions and Higgs modes. We classify such
realistic flavor models. Fixed points $\tau=i$, $e^{2\pi i/3}$ and $i\infty$ of
the modulus $\tau$ play a role in realizing a large mass hierarchy through our
scenario, where residual $S$, $ST$, and $T$ symmetries remain and the lightest
Higgs modes can correspond to eigenstates of residual symmetries at the leading
order. As a result, we find that there are 24 flavor models in total which can
be realistic in a vicinity of $S$-symmetric vacuum but no flavor models for
$ST$ and $T$-symmetric vacua.

Mass matrices with CP phase in modular flavor symmetry
Shota Kikuchi, Tatsuo Kobayashi, Morimitsu Tanimoto, Hikaru Uchida, 2022年06月17日
We study the CP violation and the CP phase of quark mass matrices in modular
flavor symmetric models. The CP symmetry remains at $\tau = e^{2 \pi i/3}$ by a
combination of the $T$-symmetry of the modular symmetry. However, the
$T$-symmetry breaking may lead to the CP violation at the fixed point $\tau =
e^{2 \pi i/3}$. We study such a possibility in magnetized orbifold models as
examples of modular flavor symmetric models. These models, in general, have
more than one candidates for Higgs modes, while generic string
compactifications also lead to several Higgs modes. These Higgs modes have
different behaviors under the $T$-transformation. The light Higgs mode can be a
linear combination of those modes so as to lead to realistic quark mass
matrices. The CP phase of mass matrix does not appear in a certain case, which
is determined by the $T$-transformation behavior. Deviation from it is
important to realize the physical CP phase. We discuss an example leading to
non-vanishing CP phase at the fixed point $\tau = e^{2 \pi i/3}$.

Modular symmetry of soft supersymmetry breaking terms
Shota Kikuchi, Tatsuo Kobayashi, Kaito Nasu, Hajime Otsuka, Shohei Takada, Hikaru Uchida, 2022年03月28日
We study the modular symmetry of soft supersymmetry breaking terms. Soft
scalar masses and $A$-term coefficients are invariant under the modular
symmetry when we regard $F$-term as a spurion with the modular weight $-2$.
Their flavor structure is determined by the same symmetry as Yukawa couplings,
i.e., fermion masses. The modular symmetric behavior of $\mu$-term and $B$-term
depends on how the $\mu$-term is generated.

Modular symmetry anomaly and non-perturbative neutrino mass terms in magnetized orbifold models
Shota Kikuchi, Tatsuo Kobayashi, Kaito Nasu, Hikaru Uchida, Shohei Uemura, 2022年02月11日
We study the modular symmetry anomaly in magnetized orbifold models. The
non-perturbative effects such as D-brane instanton effects can break tree-level
symmetry. We study which part of the modular symmetry is broken explicitly by
Majorana mass terms with three generations of neutrinos. The modular weight of
neutrino mass terms does not match with other coupling terms in tree-level
Lagrangian. In addition, the $Z_N$ symmetry of the modular flavor symmetry is
broken and a certain normal subgroup of the modular flavor symmetry remains in
neutrino mass terms.

4D modular flavor symmetric models inspired by higher dimensional theory
Shota Kikuchi, Tatsuo Kobayashi, Hajime Otsuka, Morimitsu Tanimoto, Hikaru Uchida, Kei Yamamoto, 2022年01月12日
We study a scenario to derive four-dimensional modular flavor symmetric
models from higher dimensional theory by assuming the compactification
consistent with the modular symmetry. In our scenario, wavefunctions in extra
dimensional compact space are modular forms. That leads to constraints on
combinations between modular weights and $\Gamma_N$ ($\Gamma_N')$
representations of matter fields. We also present illustrating examples.

On stringy origin of minimal flavor violation
Tatsuo Kobayashi, Hajime Otsuka, European Physical Journal C, 82, 1, 2022年01月
We study the minimal flavor violation in the context of string effective field theory. Stringy selection rules indicate that n-point couplings among fermionic zero-modes and lightest scalar modes in the string effective action are given by a product of Yukawa couplings which are regarded as spurion fields of stringy and geometrical symmetries. Hence, Yukawa couplings determine the dynamics of flavor and CP violations. This observation strongly supports the hypothesis of minimal flavor violation in the Standard Model effective field theory., 速報，短報，研究ノート等（学術雑誌）

Yukawa textures in modular symmetric vacuum of magnetized orbifold models
Shota Kikuchi, Tatsuo Kobayashi, Yuya Ogawa, Hikaru Uchida, 2021年12月03日
We study quark mass matrices derived from magnetized $T^2/\mathbb{Z}_2$
orbifold models. Yukawa matrices at three modular fixed points, $\tau=i,
e^{2\pi i/3}$ and $i\infty$ are invariant under $S$, $ST$ and
$T$-transformations. We study these invariances on $T^2/\mathbb{Z}_2$ twisted
orbifold. We find that Yukawa matrices have a kind of texture structures
although ones at $\tau=i\infty$ are not realistic. We classify Yukawa textures
at $\tau=i$ and $e^{2\pi i/3}$. Moreover we investigate the conditions such
that quark mass matrix constructed by Yukawa textures becomes approximately
rank one matrix, which is favorable to lead to hierarchical masses between the
third generation and the others. It is found that realistic quark mass matrices
can be obtained around the $S$-invariant vacuum and $ST$-invariant vacuum. As
an illustrating example, we show the realization of the quark mass ratios and
mixing based on Fritzch and Fritzch-Xing mass matrices.

Anomaly of non-Abelian discrete symmetries
Tatsuo Kobayashi, Hikaru Uchida, 2021年11月21日
We study anomalies of non-Abelian discrete symmetries; which part of
non-Abelian group is anomaly free and which part can be anomalous. It is found
that the anomaly-free elements of the group $G$ generate a normal subgroup
$G_0$ of $G$ and the residue class group $G/G_0$, which becomes the anomalous
part of $G$, is isomorphic to a single cyclic group. The derived subgroup
$D(G)$ of $G$ is useful to study the anomaly structure. This structure also
constrains the structure of the anomaly-free subgroup; the derived subgroup
$D(G)$ should be included in the anomaly-free subgroup. We study the detail
structure of the anomaly-free subgroup from the structure of the derived
subgroup in various discrete groups. For example, when $G=S_n \simeq A_n
\rtimes Z_2$ and $G=\Delta(6n^2) \simeq \Delta(3n^2) \rtimes Z_2$, in
particular, $A_n$ and $\Delta(3n^2)$ are at least included in the anomaly-free
subgroup, respectively. This result holds in any arbitrary representations.

Dark matter stability at fixed points in a modular $A_4$ symmetry
Tatsuo Kobayashi, Hiroshi Okada, Yuta Orikasa, 2021年11月10日
We propose a new mechanism of stabilization for dark matter under fixed
points of modular $A_4$ symmetry, thanks to recovering a residual symmetry for
each of fixed points at $\tau=\omega,\ i, i\times\infty$. We find that a model
at $\tau =i$ successfully reproduces the neutrino oscillation data without
conflict of the DM stability.

Majorana neutrino masses by D-brane instanton effects in magnetized orbifold models
Kouki Hoshiya, Shota Kikuchi, Tatsuo Kobayashi, Kaito Nasu, Hikaru Uchida, Shohei Uemura, 2021年03月12日
We study Majorana neutrino masses induced by D-brane instanton effects in
magnetized orbifold models. We classify possible cases, where neutrino masses
can be induced. Three and four generations are favored in order to generate
neutrino masses by D-brane instantons. Explicit mass matrices have specific
features. Their diagonalizing matrices correspond to the bimaximal mixing
matrix in the case with even magnetic fluxes, independently of the modulus
value $\tau$. On the other hand, for odd magnetic fluxes, diagonalizing
matrices correspond nearly to the tri-bimaximal mixing matrix near $\tau =i$,
while they become the bimaximal mixing matrix for larger ${\rm Im}\tau$. For
even fluxes, neutrino masses are modular forms of the weight 1 on
$T^2/\mathbb{Z}_2$, and they have symmetries such as $S_4'$ and
${\Delta'}(96)\times \mathbb{Z}_3$.

Soft supersymmetry breaking terms and lepton flavor violations in modular flavor models
Tatsuo Kobayashi, Takashi Shimomura, Morimitsu Tanimoto, 2021年02月20日
We study the soft supersymmetry (SUSY) breaking terms due to the modulus
F-term in the modular flavor models of leptons. It is found that the soft SUSY
breaking terms are constrained by the modular forms, and specific patterns are
derived. Those phenomenological implications are discussed in such as the
lepton flavor violation, $\mu \rightarrow e + \gamma$ decay. In order to
examine numerically, two modular flavor $A_4$ models are taken. The SUSY
breaking scale is significantly constrained by inputting the observed upper
bound of the $\mu \rightarrow e + \gamma$ decay. The SUSY mass scale is larger
than around $8$ TeV and $5$ TeV for the two $A_4$ models, respectively.
Therefore, the current experimental upper bound for the $\mu \to e + \gamma$
decay corresponds to the new physics of the SUSY particle at the $5$ -- $10$
TeV scale in the modular flavor models. The predicted branching ratio depends
on a modulus $\tau$ significantly. It decreases of one order at the large ${\rm
Im}\,\tau$. We also calculate the branching ratios of tauon decays to $e +
\gamma$ and $\mu + \gamma$. Predicted ones are at most ${\cal O}(10^{-15})$,
which are much below the current experimental bounds.

Modular flavor symmetries of three-generation modes on magnetized toroidal orbifolds
Shota Kikuchi, Tatsuo Kobayashi, Hikaru Uchida, 2021年01月04日
We study the modular symmetry on magnetized toroidal orbifolds with
Scherk-Schwarz phases. In particular, we investigate finite modular flavor
groups for three-generation modes on magnetized orbifolds. The three-generation
modes can be the three-dimensional irreducible representations of covering
groups and central extended groups of $\Gamma_N$ for $N=3,4,5,7,8,16$, that is,
covering groups of $\Delta(6(N/2)^2)$ for $N=$ even and central extensions of
$PSL(2,\mathbb{Z}_{N})$ for $N=$odd with Scherk-Schwarz phases. We also study
anomaly behaviors.

Classification of three generation models by orbifolding magnetized $T^2 \times T^2$
Kouki Hoshiya, Shota Kikuchi, Tatsuo Kobayashi, Yuya Ogawa, Hikaru Uchida, 2020年12月01日
We study orbifolding by the $\mathbb{Z}_2^{\rm (per)}$ permutaion of $T^2_1
\times T^2_2$ with magnetic fluxes and its twisted orbifolds. We classify the
possible three generation models which lead to non-vanishing Yukawa couplings
on the magnetized $T^2_1 \times T^2_2$ and orbifolds including the
$\mathbb{Z}_2^{\rm (per)}$ permutation and $\mathbb{Z}_2^{\rm (t)}$ twist. We
also study the modular symmetry on such orbifold models. As an illustrating
model, we examine the realization of quark masses and mixing angles.

Revisiting modular symmetry in magnetized torus and orbifold compactifications
Shota Kikuchi, Tatsuo Kobayashi, Shintaro Takada, Takuya H. Tatsuishi, Hikaru Uchida, 2020年05月26日
We study the modular symmetry in $T^2$ and orbifold comfactifications with
magnetic fluxes. There are $|M|$ zero-modes on $T^2$ with the magnetic flux
$M$. Their wavefunctions as well as massive modes behave as modular forms of
weight $1/2$ and represent the double covering group of $\Gamma \equiv
SL(2,\mathbb{Z})$, $\widetilde{\Gamma} \equiv \widetilde{SL}(2,\mathbb{Z})$.
Each wavefunction on $T^2$ with the magnetic flux $M$ transforms under
$\widetilde{\Gamma}(2|M|)$, which is the normal subgroup of
$\widetilde{SL}(2,\mathbb{Z})$. Then, $|M|$ zero-modes are representations of
the quotient group $\widetilde{\Gamma}'_{2|M|} \equiv
\widetilde{\Gamma}/\widetilde{\Gamma}(2|M|)$. We also study the modular
symmetry on twisted and shifted orbifolds $T^2/\mathbb{Z}_N$. Wavefunctions are
decomposed into smaller representations by eigenvalues of twist and shift. They
provide us with reduction of reducible representations on $T^2$.

Type II seesaw models with modular $A_4$ symmetry
Tatsuo Kobayashi, Takaaki Nomura, Takashi Shimomura, 2019年12月02日
We discuss type-II seesaw models adopting modular $A_4$ symmetry in
supersymmetric framework. In our approach, the models are classified by the
assignment of $A_4$ representations and modular weights for leptons and triplet
Higgs fields. Then neutrino mass matrix is characterized by modulus $\tau$ and
two free parameters. Carrying out numerical analysis, we find allowed parameter
sets which can fit the neutrino oscillation data. For the allowed parameter
sets, we obtain the predictions in neutrino sector such as CP violating phases
and the lightest neutrino mass. Finally we also show the predictions for the
branching ratios of doubly charged scalar boson focusing on the case where the
doubly charged scalar boson dominantly decays into charged leptons.

$CP$ violation in modular invariant flavor models
Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, Hikaru Uchida, 2019年10月25日
We study the spontaneous $CP$ violation through the stabilization of the
modulus $\tau$ in modular invariant flavor models. The $CP$-invaraiant
potentential has the minimum only at ${\rm Re}[\tau] = 0$ or 1/2. From this
prediction, we study $CP$ violation in modular invariant flavor models. The
physical $CP$ phase is vanishing. The important point for the $CP$ conservation
is the $T$ transformation in the modular symmetry. One needs the violation of
$T$ symmetry to realize the spontaneous $CP$ violation.

$A_4$ lepton flavor model and modulus stabilization from $S_4$ modular symmetry
Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, 2019年09月09日
We study the modulus stabilization in an $A_4$ model whose $A_4$ flavor
symmetry is originated from the $S_4$ modular symmetry. We can stabilize the
modulus so that the $A_4$ invariant superpotential leads to the realistic
lepton masses and mixing angles. We also discuss the phenomenological aspect of
the present model as a consequence of the modulus stabilization.

New $A_4$ lepton flavor model from $S_4$ modular symmetry
Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, 2019年07月22日
We study a flavor model with $A_4$ symmetry which originates from $S_4$
modular group. In $S_4$ symmetry, $Z_2$ subgroup can be anomalous, and then
$S_4$ can be violated to $A_4$. Starting with a $S_4$ symmetric Lagrangian at
the tree level, the Lagrangian at the quantum level has only $A_4$ symmetry
when $Z_2$ in $S_4$ is anomalous. We obtain modular forms of two singlets and a
triplet representations of $A_4$ by decomposing $S_4$ modular forms into $A_4$
representations. We propose a new $A_4$ flavor model of leptons by using those
$A_4$ modular forms. We succeed in constructing a viable neutrino mass matrix
through the Weinberg operator for both normal hierarchy (NH) and inverted
hierarchy (IH) of neutrino masses. Our predictions of the CP violating Dirac
phase $\delta_{CP}$ and the mixing $\sin^2\theta_{23}$ depend on the sum of
neutrino masses for NH.

Modular $S_3$ invariant flavor model in SU(5) GUT
Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, 2019年06月25日
We present a flavor model with the $S_3$ modular invariance in the framework
of SU(5) GUT. The $S_3$ modular forms of weights $2$ and $4$ give the quark and
lepton mass matrices with a common complex parameter, the modulus $\tau$. The
GUT relation of down-type quarks and charged leptons is imposed by the VEV of
adjoint 24-dimensional Higgs multiplet in addition to the VEVs of $5$ and $\bar
5$ Higgs multiples of SU(5). The observed CKM and PMNS mixing parameters as
well as the mass eigenvalues are reproduced properly. We discuss the leptonic
CP phase and the effective mass of the neutrinoless double beta decay with the
sum of neutrino masses.

Modular symmetry anomaly in magnetic flux compactification
Yuki Kariyazono, Tatsuo Kobayashi, Shintaro Takada, Shio Tamba, Hikaru Uchida, 2019年04月16日
We study modular symmetry anomalies in four-dimensional low-energy effective
field theory, which is derived from six-dimensional supersymmetric $U(N)$
Yang-Mills theory by magnetic flux compactification. The gauge symmetry $U(N)$
is broken to $U(N_a) \times U(N_b)$ by magnetic fluxes. It is found that
Abelian subgroup of the modular symmetry corresponding to discrete part of
$U(1)$ can be anomalous, but other elements independent of $U(1)$ in the
modular symmetry are always anomaly-free.

Finite modular subgroups for fermion mass matrices and baryon/lepton number violation
Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, Hikaru Uchida, 2018年12月23日
We study a flavor model that the quark sector has the $S_3$ modular
symmetry,while the lepton sector has the $A_4$ modular symmetry. Our model
leads to characteristic quark mass matrices which are consistent with
experimental data of quark masses, mixing angles and the CP violating phase.
The lepton sector is also consistent with the experimental data of neutrino
oscillations. We also study baryon and lepton number violations in our flavor
model.

Modular forms of finite modular subgroups from magnetized D-brane models
Tatsuo Kobayashi, Shio Tamba, 2018年11月28日
We study modular transformation of holomorphic Yukawa couplings in magnetized
D-brane models. It is found that their products are modular forms, which are
non-trivial representations of finite modular subgroups, e.g. $S_3$, $S_4$,
$\Delta(96)$ and $\Delta(384)$.

Non-Universal Gaugino Masses in the NMSSM
Junichiro Kawamura, Tatsuo Kobayashi, Natsumi Nagata, 2018年08月24日
The Next-to-Minimal Supersymmetric Standard Model (NMSSM) provides a natural

framework to realize a low-scale supersymmetric (SUSY) model, where a singlet

superfield is added to the minimal model to generate a SUSY-scale higgsino mass

term with its vacuum expectation value. Due to the presence of the extra

singlet field, the vacuum conditions to realize the correct electroweak

symmetry-breaking become fairly restrictive especially if we impose

universality conditions at the unification scale. In this paper, we show that a

non-universal gaugino mass spectrum can significantly relax this restriction

even though the scalar masses and trilinear couplings are subject to

universality conditions. With the gaugino non-universality, we find that

higgsino can be the lightest SUSY particle and its thermal relic abundance can

reproduce the observed dark matter density in a wide range of parameter space

in which the 125~GeV Higgs-boson mass is obtained. This higgsino-like dark

matter may be probed in direct detection experiments. We also find that there

is an upper bound on the masses of supersymmetric particles in this scenario,

and many model points predict colored particles such as gluino to be within the

reach of a future 100~TeV collider. Implications for no-scale/gaugino-mediation

models are also discussed., 機関テクニカルレポート，技術報告書，プレプリント等

Modular $A_4$ invariance and neutrino mixing
Tatsuo Kobayashi, Naoya Omoto, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, 2018年08月09日
We study the phenomenological implications of the modular symmetry $\Gamma(3)

\simeq A_4$ of lepton flavors facing recent experimental data of neutrino

oscillations. The mass matrices of neutrinos and charged leptons are

essentially given by fixing the expectation value of modulus $\tau$, which is

the only source of modular invariance breaking. We introduce no flavons in

contrast with the conventional flavor models with $A_4$ symmetry. We classify

our neutrino models along with the type I seesaw model, the Weinberg operator

model and the Dirac neutrino model. In the normal hierarchy of neutrino masses,

the seesaw model is available by taking account of recent experimental data of

neutrino oscillations and the cosmological bound of sum of neutrino masses. The

predicted $\sin^2\theta_{23}$ is restricted to be larger than $0.54$ and

$\delta_{CP}=\pm (50^{\circ}\mbox{--}180^{\circ})$. Since the correlation of

$\sin^2\theta_{23}$ and $\delta_{CP}$ is sharp, the prediction is testable in

the future. It is remarkable that the effective mass $m_{ee}$ of the

neutrinoless double beta decay is around $22$\,meV while the sum of neutrino

masses is predicted to be $145$\,meV. On the other hand, for the inverted

hierarchy of neutrino masses, only the Dirac neutrino model is consistent with

the experimental data., 機関テクニカルレポート，技術報告書，プレプリント等

Predictive neutrino mass textures with origin of flavor symmetries
Tatsuo Kobayashi, Takaaki Nomura, Hiroshi Okada, Phys. Rev. D 98, 055025 (2018), 2018年05月18日
We investigate origins of predictive one-zero neutrino mass textures in a

systematic way. Here we search Abelian continuous(discrete) global symmetries,

and non-Abelian discrete symmetries, and show how to realize these neutrino

masses. Then we propose a concrete model involving a dark matter candidate and

an extra gauge boson, and show their phenomenologies., 機関テクニカルレポート，技術報告書，プレプリント等

Radiative Kähler moduli stabilization
Tatsuo Kobayashi, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi, Phys. Rev. D 97, 106006 (2018), 97, 10, 2018年05月15日
We propose a new type of K\"ahler moduli stabilization mechanisms in type IIB

superstring theory on Calabi-Yau manifolds with the positive Euler number. The

overall K\"ahler modulus can be perturbatively stabilized by radiative

corrections due to sparticles. Its minimum is the anti-de Sitter vacuum, where

supersymmetry is broken. We can uplift it to the de Sitter vacuum by

introducing anti-D-branes, keeping the modulus stabilized. Although our

numerical results depend on the choice of the cutoff scale and degeneracies of

sparticles, at any rate there exist the parameter spaces where the masses of

Kaluza-Klein and stringy modes are larger than the cutoff scale. Furthermore,

this stabilization scenario predicts an ultralight axion., American Physical Society, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Modular symmetry and non-Abelian discrete flavor symmetries in string compactification
Tatsuo Kobayashi, Satoshi Nagamoto, Shintaro Takada, Shio Tamba, Takuya H. Tatsuishi, Phys. Rev. D 97, 116002 (2018), 2018年04月18日
We study the modular symmetry in magnetized D-brane models on $T^2$.

Non-Abelian flavor symmetry $D_4$ in the model with magnetic flux $M=2$ (in a

certain unit) is a subgroup of the modular symmetry. We also study the modular

symmetry in heterotic orbifold models. The $T^2/Z_4$ orbifold model has the

same modular symmetry as the magnetized brane model with $M=2$, and its flavor

symmetry $D_4$ is a subgroup of the modular symmetry., 機関テクニカルレポート，技術報告書，プレプリント等

Modulus D-term inflation
Kenji Kadota, Tatsuo Kobayashi, Ikumi Saga, Keigo Sumita, Journal of High Energy Physics, 2018, 4, 2018年04月01日
We propose a new model of single-field D-term inflation in supergravity, where the inflation is driven by a single modulus field which transforms non-linearly under the U(1) gauge symmetry. One of the notable features of our modulus D-term inflation scenario is that the global U(1) remains unbroken in the vacuum and hence our model is not plagued by the cosmic string problem which can exclude most of the conventional D-term inflation models proposed so far due to the CMB observations., Springer Verlag, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Neutrino mixing from finite modular groups
Tatsuo Kobayashi, Kentaro Tanaka, Takuya H. Tatsuishi, Phys. Rev. D 98, 016004 (2018), 2018年03月28日
We study the lepton flavor models, whose flavor symmetries are finite

subgroups of the modular group such as $S_3$ and $A_4$. In our models,

couplings are also nontrivial representations of these groups and modular

functions of the modulus. We study the possibilities that these models realize

realistic values of neutrino masses and lepton mixing angles., 機関テクニカルレポート，技術報告書，プレプリント等

A viable D-term hybrid inflation model
Kenji Kadota, Tatsuo Kobayashi, Keigo Sumita, Journal of Cosmology and Astroparticle Physics, 2017, 11, 2017年11月21日
We propose a new model of the D-term hybrid inflation in the framework of supergravity. Although our model introduces, analogously to the conventional D-term inflation, the inflaton and a pair of scalar fields charged under a U(1) gauge symmetry, we study the logarithmic and exponential dependence on the inflaton field, respectively, for the Kähler and superpotential. This results in a characteristic one-loop scalar potential consisting of linear and exponential terms, which realizes the small-field inflation dominated by the Fayet-Iliopoulos term. With the reasonable values for the coupling coefficients and, in particular, with the U(1) gauge coupling constant comparable to that of the Standard Model, our D-term inflation model can solve the notorious problems in the conventional D-term inflation, namely, the CMB constraints on the spectral index and the generation of cosmic strings., Institute of Physics Publishing, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Realization of a spontaneous gauge and supersymmetry breaking vacuum
Tatsuo Kobayashi, Yuji Omura, Osamu Seto, Kazuki Ueda, JOURNAL OF HIGH ENERGY PHYSICS, 11, 2017年11月
It is one of the major issues to realize a vacuum which breaks supersymmetry (SUSY) and R-symmetry, in a supersymmetric model. We study the model, where the same sector breaks the gauge symmetry and SUSY. In general, the SUSY breaking model without gauge symmetry has a flat direction at the minimum of F-term scalar potential. When we introduce U(1) gauge symmetry to such a SUSY breaking model, there can appear a runaway direction. Such a runway direction can be lifted by loop effects, and the gauge symmetry breaking and SUSY breaking are realized. The R-symmetry, that is assigned to break SUSY, is also spontaneously broken at the vacuum. This scenario can be extended to non-Abelian gauge theories. We also discuss application to the Pati-Salam model and the SU(5) grand unified theory. We see that non-vanishing gaugino masses are radiatively generated by the R-symmetry breaking and the gauge messenger contribution., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Zero-modes on orbifolds: Magnetized orbifold models by modular transformation
Tatsuo Kobayashi, Satoshi Nagamoto, PHYSICAL REVIEW D, 96, 9, 2017年11月
We study T-2/Z(N) orbifold models with magnetic fluxes. We propose a systematic way to analyze the number of zero-modes and their wave functions by use of modular transformation. Our results are consistent with the previous results, and our approach is more direct and analytical than the previous ones. The index theorem implies that the zero-mode number of the Dirac operator on T-2 is equal to the index M, which corresponds to the magnetic flux in a certain unit. Our results show that the zero-mode number of the Dirac operator on T-2/Z(N) is equal to left perpendicularM/Nright perpendicular + 1 except one case on the T-2/Z(3) orbifold., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Relaxion window
Tatsuo Kobayashi, Osamu Seto, Takashi Shimomura, Yuko Urakawa, MODERN PHYSICS LETTERS A, 32, 27, 2017年09月
We investigate cosmological constraints on the original relaxion scenario proposed by Graham, Kaplan and Rajendran. We first discuss the appropriate sign choice of the terms in the scalar potential, when the QCD axion is the relaxion with a relaxion-inflaton coupling proposed in the original paper. We next derive the cosmologically consistent ranges of the mass and a coupling of the relaxion for both the QCD relaxion and non-QCD relaxion. The mass range is obtained by 10(-5) eV << m(phi) less than or similar to 10(4) eV. We also find that a strong correlation between the Hubble parameter at the relaxion stabilization and the scale A of non-QCD strong dynamics, which generates the non-perturbative relaxion cosine potential. For a higher relaxion mass, a large scale A becomes available. However, for its lower mass, A should be small and constructing such a particle physics model is challenging., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Supersymmetry preserving and breaking degenerate vacua, and radiative moduli stabilization
Tatsuo Kobayashi, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi, PHYSICAL REVIEW D, 96, 4, 2017年08月
We propose a new type of moduli stabilization scenario where the supersymmetric and supersymmetry-breaking minima are degenerate at the leading level. The inclusion of the loop corrections originating from the matter fields resolves this degeneracy of vacua. Light axions are predicted in one of our models., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Kähler moduli stabilization in semi-realistic magnetized orbifold models
Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Shohei Uemura, Phys. Rev. D 96, 026019 (2017), 96, 2, 2017年07月
We study K\"ahler moduli stabilizations in semi-realistic magnetized D-brane

models based on $ Z_2\times Z_2'$ toroidal orbifolds. In type IIB

compactifications, 3-form fluxes can stabilize the dilaton and complex

structure moduli fields, but there remain some massless closed string moduli

fields, K\"ahler moduli. The magnetic fluxes generate Fayet-Iliopoulos terms,

which can fix ratios of K\"ahler moduli. On top of that, we consider D-brane

instanton effects to stabilize them in concrete D-brane models and investigate

the brane configurations to confirm that the moduli fields can be stabilized

successfully. In this paper, we treat two types of D-brane models. One is based

on D9-brane systems respecting the Pati-Salam model. The other is realized in a

D7-brane system breaking the Pati-Salam gauge group. We find suitable

configurations where the D-brane instantons can stabilize the moduli fields

within both types of D-brane models, explaining an origin of a small constant

term of the superpotential which is a key ingredient for successful moduli

stabilizations., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Polyinstanton axion inflation
Tatsuo Kobayashi, Shohei Uemura, Junji Yamamoto, PHYSICAL REVIEW D, 96, 2, 2017年07月
We investigate the axion inflation model derived by polyinstanton effects in type II superstring theories. Polyinstanton effects are instanton effects corrected by another instanton and they can generate the modulus-axion potential with the double exponential function. Although the axion has a period of small value, this potential can have a flat region because its derivatives are exponentially suppressed by nonperturbative effects. From the view point of the cosmic inflation, such a potential is interesting. In this paper, we numerically study the possibilities of realizing the cosmic inflation. We also study their spectral index and other cosmological observables, numerically., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Axion inflation and Affleck-Dine baryogenesis
Kensuke Akita, Tatsuo Kobayashi, Hajime Otsuka, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 4, 2017年04月
String theory generically predicts the coupling between the Affleck-Dine field and axion field through higher-dimensional operators. We thus explore the Affleck-Dine baryogenesis on an axion background. It turns out that the axion oscillation produces an enough amount of baryon asymmetry of the Universe just after the inflation, even without a soft supersymmetry-breaking A-term. This baryogenesis scenario is applicable to the string axion inflation., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

CP-violating phase on magnetized toroidal orbifolds
Tatsuo Kobayashi, Kenji Nishiwaki, Yoshiyuki Tatsuta, JOURNAL OF HIGH ENERGY PHYSICS, 4, 2017年04月
We study the CP-violating phase of the quark sector on T-2/Z(N) (N = 2, 3, 4, 6) with non-vanishing magnetic fluxes, where properties of possible origins of the CP violation are investigated minutely. In this system, a non-vanishing value is mandatory in the real part of the complex modulus parameter tau of the two-dimensional torus in order to explain the CP violation in the quark sector. On T-2 without orbifolding, underlying discrete flavor symmetries severely restrict the form of Yukawa couplings and it is very difficult to reproduce the observed pattern in the quark sector including the CP-violating phase delta(CP). When multiple Higgs doublets emerge on T-2/Z(2), the mass matrices of the zero -mode fermions can be written in the Gaussian textures by choosing appropriate configurations of vacuum expectation values of the Higgs fields. When such Gaussian textures of mass matrices are realized, we show that all of the quark profiles, which are mass hierarchies among the quarks, quark mixing angles, and delta(CP) can be simultaneously realized., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Toward pole inflation and attractors in supergravity : Chiral matter field inflation
Tatsuo Kobayashi, Osamu Seto, Takuya H. Tatsuishi, 2017年03月29日
In string-inspired supergravity theory, K\"{a}hler metric of chiral matter

fields often has a pole. Such K\"{a}hler metric is interesting from the

viewpoint of the framework of the pole inflation, where the scalar potential

can be stretched out to be flat around the pole for a canonically normalized

field and inflation can be realized. However, when K\"{a}hler metric has a

pole, the scalar potential can also have a pole at the same point in

supergravity theory. We study such supergravity models with the pole, and

provide numerical analysis of inflationary dynamics and resultant density

perturbation. In contrast with usual pole inflation models, inflation in this

supergravity based model occurs not on the pole but region apart from the pole.

We show that the existence of the pole in the scalar potential is crucial

nevertheless. We also examine attractor behavior of our model., 機関テクニカルレポート，技術報告書，プレプリント等

Constraints on small-field axion inflation
Tatsuo Kobayashi, Akane Oikawa, Naoya Omoto, Hajime Otsuka, Ikumi Saga, PHYSICAL REVIEW D, 95, 6, 2017年03月
We study general class of small-field axion inflations, which are the mixture of polynomial and sinusoidal functions suggested by the natural and axion monodromy inflations. The axion decay constants leading to the successful axion inflations are severely constrained in order not to spoil the big bang nucleosynthesis and overproduce the isocurvature perturbation originating from the QCD axion. We in turn find that the cosmologically favorable axion decay constants are typically of order the grand unification scale or the string scale, which is consistent with the prediction of closed-string axions., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Supersymmetric models on magnetized orbifolds with flux-induced Fayet-Iliopoulos terms
Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Yoshiyuki Tatsuta, PHYSICAL REVIEW D, 95, 1, 2017年01月
We study supersymmetric (SUSY) models derived from the ten-dimensional SUSY Yang-Mills theory compactified on magnetized orbifolds, with nonvanishing Fayet-Iliopoulos (FI) terms induced by magnetic fluxes in extra dimensions. Allowing the presence of FI- terms relaxes a constraint on flux configurations in SUSY model building based on magnetized backgrounds. In this case, charged fields develop their vacuum expectation values to cancel the FI- terms in the D-flat directions of fluxed gauge symmetries, which break the gauge symmetries and lead to a SUSY vacuum. Based on this idea, we propose a new class of SUSY magnetized orbifold models with three generations of quarks and leptons. Especially, we construct a model where the right-handed sneutrinos develop their vacuum expectation values which restore the supersymmetry but yield lepton number violating terms below the compactification scale, and show their phenomenological consequences., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Flavor structure in SO(32) heterotic string theory
Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano, Takuya H. Tatsuishi, PHYSICAL REVIEW D, 94, 12, 2016年12月
We study the flavor structure in SO(32) heterotic string theory on six-dimensional tori with magnetic fluxes. Specifically, we focus on models with the flavor symmetries SU(3)(f) and Delta(27). In both models, we can realize the realistic quark masses and mixing angles., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Small field axion inflation with sub-Planckian decay constant
Kenji Kadota, Tatsuo Kobayashi, Akane Oikawa, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 10, 2016年10月
We study an axion inflation model recently proposed within the framework of type IIB superstring theory, where we pay a particular attention to a sub-Planckian axion decay constant. Our axion potential can lead to the small field inflation with a small tensor-to-scalar ratio, and a typical reheating temperature can be as low as GeV., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dynamical supersymmetry breaking on magnetized tori and orbifolds
Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, NUCLEAR PHYSICS B, 911, 606, 622, 2016年10月
We construct several dynamical supersymmetry breaking (DSB) models within a single ten-dimensional supersymmetric Yang-Mills (SYM) theory, compactified on magnetized tori with or without orbifolding. We study the case that the supersymmetry breaking is triggered by a strong dynamics of SU(NC) SYM theory with N-F flavors contained in the four-dimensional effective theory. We show several configurations of magnetic fluxes and orbifolds, those potentially yield, below the compactification scale, the field contents and couplings required for triggering DSB. We especially find a class of self-complete DSB models on orbifolds, where all the extra fields are eliminated by the orbifold projection and DSB successfully occurs within the given framework. Comments on some perspectives for associating the obtained DSB models with the other sectors, such as the visible sector and another hidden sector for, e.g., stabilizing moduli, are also given. (C) 2016 The Authors. Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dilaton stabilization in three-generation heterotic string model
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino, PHYSICS LETTERS B, 760, 63, 68, 2016年09月
We study dilaton stabilization in heterotic string models. By utilizing the asymmetric orbifold construction, we construct an explicit three-generation model whose matter content in the visible sector is the supersymmetric standard model with additional vectorlike matter. This model does not contain any geometric moduli fields except the dilaton field. Model building at a symmetry enhancement point in moduli space enlarges the rank of the hidden gauge group. By analyzing multiple hidden gauge sectors, the dilaton field is stabilized by the racetrack mechanism. We also discuss a supersymmetry breaking scenario and F-term uplifting. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Modular symmetry in magnetized/intersecting D-brane models
Tatsuo Kobayashi, Satoshi Nagamoto, Shohei Uemura, 2016年08月22日
We study the modular symmetry in four-dimensional low-energy effective field

theory, which is derived from type IIB magnetized D-brane models and type IIA

intersecting D-brane models. We analyze modular symmetric behaviors of

perturbative terms and non-perturbative terms induced by D-brane instanton

effects. Anomalies are also investigated and such an analysis on anomalies

suggests corrections in effective field theory., 機関テクニカルレポート，技術報告書，プレプリント等

Comprehensive analysis of Yukawa hierarchies on T-2/Z(N) with magnetic fluxes
Yukihiro Fujimoto, Tatsuo Kobayashi, Kenji Nishiwaki, Makoto Sakamoto, Yoshiyuki Tatsuta, PHYSICAL REVIEW D, 94, 3, 2016年08月
Based on the results of the classification by T.-h. Abe et al., Nucl. Phys. B894, 374 (2015)., we exhaustively investigate Yukawa sector of U(8) model on magnetized orbifolds T-2 / Z(2), T-2 / Z(3), T-2 / Z(4) and T-2 / Z(6) by evaluating ratios of the mass eigenvalues of the three states in all the possible configurations with one and two Higgs pairs where three generations are realized in fermions. Because of the smearing effect via kinetic mixing, one can realize a hierarchy such as 10(-2)-10(-3), but it is very difficult to achieve the mass ratio between the up and top quarks (m(up) / m(top) similar to 10(-5)) on the complicated magnetized orbifolds T-2 / Z(N) (N similar to 3,4,6)., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Modular invariant inflation
Tatsuo Kobayashi, Daisuke Nitta, Yuko Urakawa, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 8, 2016年08月
Modular invariance is a striking symmetry in string theory, which may keep stringy corrections under control. In this paper, we investigate a phenomenological consequence of the modular invariance, assuming that this symmetry is preserved as well as in a four dimensional (4D) low energy effective field theory. As a concrete setup, we consider a modulus field T whose contribution in the 4D effective field theory remains invariant under the modular transformation and study inflation drived by T. The modular invariance restricts a possible form of the scalar potenntial. As a result, large field models of inflation are hardly realized. Meanwhile, a small field model of inflation can be still accomodated in this restricted setup. The scalar potential traced during the slow-roll inflation mimics the hilltop potential V-ht, but it also has a non-negligible deviation from V-ht. Detecting the primordial gravitational waves predicted in this model is rather challenging. Yet, we argue that it may be still possible to falsify this model by combining the information in the reheating process which can be determined self-completely in this setup., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Gauge coupling unification in SO(32) heterotic string theory with magnetic fluxes
Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano, Takuya H. Tatsuishi, PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, 5, 2016年05月
We study SO(32) heterotic string theory on a torus with magnetic fluxes. Non-vanishing fluxes can lead to non-universal gauge kinetic functions for SU(3) x SU(2) x U(1)gamma, which is an important feature of SO(32) heterotic string theory in contrast to the E-8 x E-8 theory. It is found that the experimental values of gauge couplings are realized with O(1) values of moduli fields based on realistic models with the SU(3) x SU(2) x U(1)gamma gauge symmetry and three chiral generations of quarks and leptons without chiral exotics., OXFORD UNIV PRESS INC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Moduli mediation without moduli-induced gravitino problem
Kensuke Akita, Tatsuo Kobayashi, Akane Oikawa, Hajime Otsuka, JOURNAL OF HIGH ENERGY PHYSICS, 5, 2016年05月
We study the moduli-induced gravitino problem within the framework of the phenomenologically attractive mirage mediations. The huge amount of gravitino generated by the moduli decay can be successfully diluted by introducing an extra light modulus field which does not induce the supersymmetry breaking. Since the lifetime of extra modulus field becomes longer than usually considered modulus field, our proposed mechanism is applied to both the low- and high-scale supersymmetry breaking scenarios. We also point out that such an extra modulus field appears in the flux compactification of type II string theory., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

New potentials for string axion inflation
Tatsuo Kobayashi, Akane Oikawa, Hajime Otsuka, PHYSICAL REVIEW D, 93, 8, 2016年04月
We propose a new type of axion inflation with complex structure moduli in the framework of type IIB superstring theory compactified on the Calabi-Yau manifold. The inflaton is identified as the axion for the complex structure moduli whose potential is originating from instantonic corrections appearing through the period vector of the mirror Calabi-Yau manifold. The axionic shift symmetry is broken down to the discrete one by the inclusion of the instantonic correction and certain three-form fluxes. Our proposed inflation scenario is compatible with Kahler moduli stabilization. We also study a typical reheating temperature in the case of complex structure moduli inflation., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Majorana neutrino mass structure induced by rigid instantons on toroidal orbifold
Tatsuo Kobayashi, Yoshiyuki Tatsuta, Shohei Uemura, PHYSICAL REVIEW D, 93, 6, 2016年03月
We study the effects of D-brane instantons wrapping rigid cycles on the Z(2) x Z(2)' toroidal orbifold. We compute Majorana masses induced by rigid D-brane instantons and realize bimaximal mixing matrices in certain models. We can also derive more generic mass matrices in other models. The bimaximal mixing Majorana mass matrix provides a possibility for explaining observed mixing angles. We also compute the mu-term matrix among more than one pair of Higgs fields induced by rigid D-brane instantons., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenology of NMSSM in TeV scale mirage mediation
Kei Hagimoto, Tatsuo Kobayashi, Hiroki Makino, Ken-ichi Okumura, Takashi Shimomura, JOURNAL OF HIGH ENERGY PHYSICS, 2, 2016年02月
We study the next-to-minimal supersymmetric standard model (NMSSM) with the TeV scale mirage mediation, which is known as a solution for the little hierarchy problem in supersymmetry. Our previous study showed that 125 GeV Higgs boson is realized with O (10)% fine-tuning for 1.5 TeV gluino (1TeV stop) mass. The mu term could be as large as 500 GeV without sacrificing the fine-tuning thanks to a cancellation mechanism. The singlet-doublet mixing is suppressed by tan beta. In this paper, we further extend this analysis. We argue that approximate scale symmetries play a role behind the suppression of the singlet-doublet mixing. They reduce the mixing matrix to a simple form that is useful to understand the results of the numerical analysis. We perform a comprehensive analysis of the fine-tuning including the singlet sector by introducing a simple formula for the fine-tuning measure. This shows that the singlet mass of the least fine-tuning is favored by the LEP anomaly for moderate tan beta. We also discuss prospects for the precision measurements of the Higgs couplings at LHC and ILC and direct/indirect dark matter searches in the model., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Axion inflation with cross-correlated axion isocurvature perturbations
Kenji Kadota, Tatsuo Kobayashi, Hajime Otsuka, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 1, 2016年01月
We study the inflation scenarios, in the framework of superstring theory, where the inflaton is an axion producing the adiabatic curvature perturbations while there exists another light, axion producing the isocurvature perturbations. We discuss how the non-trivial couplings among string axions can generically arise, and calculate the consequent cross-correlations between the adiabatic and isocurvature modes through concrete examples. Based on the Planck analysis on the generally correlated isocurvature perturbations, we show that there is a preference for the existence of the correlated isocurvature modes for the axion monodromy inflation while the natural inflation disfavors such isocurvature modes., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Entropy production by domain wall decay in the NMSSM
Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto, PHYSICAL REVIEW D, 92, 10, 2015年11月
We consider domain walls in the Z(3) symmetric next-to-minimal supersymmetric standard model. The spontaneous Z(3) discrete symmetry breaking produces domain walls, and the stable domain walls are problematic. Thus, we assume the Z(3) symmetry is slightly but explicitly broken and the domain walls decay. Such a decay causes a large late-time entropy production. We study its cosmological implications on unwanted relics such as the moduli, gravitino, lightest superparticle, and axion., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Realistic three-generation models from SO (32) heterotic string theory
Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano, JOURNAL OF HIGH ENERGY PHYSICS, 9, 2015年09月
We search for realistic supersymmetric standard-like models from SO(32) heterotic string theory on factorizable tori with multiple magnetic fluxes. Three chiral ganerations of quarks and leptons are derived from the adjoint and vector representations of SO(12) gauge groups embedded in SO(32) adjoint representation. Massless spectra of our models also include Higgs fields, which have desired Yukawa couplings to quarks and leptons at the tree-level., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Standard model-like D-brane models and gauge couplings
Yuta Hamada, Tatsuo Kobayashi, Shohei Uemura, NUCLEAR PHYSICS B, 897, 563, 582, 2015年08月
We systematically search intersecting D-brane models, which just realize the Standard Model chiral matter contents and gauge symmetry. We construct new classes of non-supersymmetric Standard Model-like models. We also study the gauge coupling constants of these models. The tree level gauge coupling is a function of the compactification moduli, the string scale, the string coupling and the winding numbers of D-branes. By tuning them, we examine whether the models can explain the experimental values of gauge couplings. As a result, we find that the string scale should be greater than 10(14-15) GeV if the compactification scale and the string scale are of the same order. (C) 2015 The Authors. Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dilution of axion dark radiation by thermal inflation
Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto, PHYSICAL REVIEW D, 92, 2, 2015年07月
Axions in the Peccei-Quinn (PQ) mechanism provide a promising solution to the strong CP problem in the standard model of particle physics. Coherently generated PQ scalar fields could dominate the energy density in the early Universe and decay into relativistic axions, which would conflict with the current dark radiation constraints. We study the possibility that a thermal inflation driven by a U(1) gauged Higgs field dilutes such axions. A well-motivated extra gauged U(1) would be the local B - L symmetry. We also discuss the implication for the case of U(1)(B-L) and an available baryogenesis mechanism in such cosmology., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

D-brane instanton induced mu terms and their hierarchical structure
Hiroyuki Abe, Tatsuo Kobayashi, Yoshiyuki Tatsuta, Shohei Uemura, PHYSICAL REVIEW D, 92, 2, 2015年07月
We study the mu-term matrix of Higgs pairs induced by the D-brane instanton effects in intersecting D6-brane models compactified on T-6. It is found that the mu-term matrix has a certain permutation symmetry and its eigenvalues have large hierarchical structure without fine-tuning., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Beginning of Universe through large field hybrid inflation
Tatsuo Kobayashi, Osamu Seto, MODERN PHYSICS LETTERS A, 30, 21, 2015年07月
Recent detection of B-mode polarization induced from tensor perturbations by the BICEP2 experiment implies the so-called large field inflation, where an inflaton field takes super-Planckian expectation value during inflation, at a high energy scale. We show however, if another inflation follows hybrid inflation, the hybrid inflation can generate a large tensor perturbation with not super-Planckian but Planckian field value. This scenario would relax the tension between BICEP2 and Planck concerning the tensor-to-scalar ratio, because a negative large running can also be obtained for a certain number of e-fold of the hybrid inflation. A natural interpretation of a large gravitational wave mode with or without the scalar spectral running might be multiple inflation in the early Universe., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Towards natural inflation from weakly coupled heterotic string theory
Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, 6, 2015年06月
We propose natural inflation from the heterotic string theory on the "Swiss-Cheese" Calabi-Yau manifold with multiple U(1) magnetic fluxes. Such multiple U(1) magnetic fluxes stabilize the same number of the linear combination of the universal axion and Kahler axions, and one of the Kahler axions is identified as the inflaton. This axion decay constant can be determined by the size of one-loop corrections to the gauge kinetic function of the hidden gauge groups, which leads effectively to the trans-Planckian axion decay constant consistent with the Planck data. During the inflation, the real parts of the moduli are also stabilized by employing the nature of the "Swiss-Cheese" Calabi-Yau manifold., OXFORD UNIV PRESS INC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Study of lepton flavor violation in flavor symmetric models for lepton sector
Tatsuo Kobayashi, Yuji Omura, Fumihiro Takayama, Daiki Yasuhara, 2015年05月28日
Flavor symmetric model is one of the attractive Beyond Standard Models (BSMs)

to reveal the flavor structure of the Standard Model (SM). A lot of efforts

have been put into the model building and we find many kinds of flavor

symmetries and setups are able to explain the observed fermion mass matrices.

In this paper, we look for common predictions of physical observables among the

ones in flavor symmetric models, and try to understand how to test flavor

symmetry in experiments. Especially, we focus on the BSMs for leptons with

extra Higgs $SU(2)_L$ doublets charged under flavor symmetry. In many flavor

models for leptons, remnant symmetry is partially respected after the flavor

symmetry breaking, and it controls well the Flavor Changing Neutral Currents

(FCNCs) and suggests some crucial predictions against the flavor changing

process, although the remnant symmetry is not respected in the full lagrangian.

In fact, we see that $\tau^- \to e^+ \mu^- \mu^-$ $( \mu^+ e^- e^-)$ and $e^+

e^- \to \tau^+\tau^-$ $(\mu^-\mu^+)$ processes are the most important in the

flavor models that the extra Higgs doublets belong to triplet representation of

flavor symmetry. For instance, the stringent constraint from the $\mu \to e

\gamma$ process could be evaded according to the partial remnant symmetry. We

also investigate the breaking effect of the remnant symmetry mediated by the

Higgs scalars, and investigate the constraints from the flavor physics: the

flavor violating $\tau$ and $\mu$ decays, the electric dipole moments, and the

muon anomalous magnetic moment. We also discuss the correlation between FCNCs

and nonzero $\theta_{13}$, and point out the physical observables in the

charged lepton sector to test the BSMs for the neutrino mixing., 機関テクニカルレポート，技術報告書，プレプリント等

Classification of three-generation models on magnetized orbifolds
Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto, Yoshiyuki Tatsuta, NUCLEAR PHYSICS B, 894, 374, 406, 2015年05月
We classify the combinations of parameters which lead three generations of quarks and leptons in the framework of magnetized twisted orbifolds on T-2/Z(2), T-2/Z(3), T-2/Z(4) and T-2/Z(6) with allowing nonzero discretized Wilson line phases and Scherk-Schwarz phases. We also analyze two actual examples with nonzero phases leading to one-pair Higgs and five-pair Higgses and discuss the difference from the results without nonzero phases studied previously. (Note: this article is registered under preprint number: arXiv:1501.02787 [hep-ph].) (C) 2015 The Authors. Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Natural inflation with and without modulations in type IIB string theory
Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, JOURNAL OF HIGH ENERGY PHYSICS, 4, 2015年04月
We propose a mechanism for the natural inflation with and without modulation in the framework of type IIB string theory on toroidal orientifold or orbifold. We explicitly construct the stabilization potential of complex structure, dilaton and Kahler moduli, where one of the imaginary component of complex structure moduli becomes light which is identified as the inflaton. The inflaton potential is generated by the gaugino-condensation term which receives the one-loop threshold corrections determined by the field value of complex structure moduli and the axion decay constant of inflaton is enhanced by the inverse of one-loop factor. We also find the threshold corrections can also induce the modulations to the original scalar potential for the natural inflation. Depending on these modulations, we can predict several sizes of tensor-to-scalar ratio as well as the other cosmological observables reported by WMAP, Planck and/or BICEP2 collaborations., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Gauge extension of non-Abelian discrete flavor symmetry
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino, JOURNAL OF HIGH ENERGY PHYSICS, 3, 2015年03月
We investigate a gauge theory realization of non-Abelian discrete flavor symmetries and apply the gauge enhancement mechanism in heterotic orbifold models to field-theoretical model building. Several phenomenologically interesting non-Abelian discrete symmetries are realized effectively from a U(1) gauge theory with a permutation symmetry. We also construct a concrete model for the lepton sector based on a U(1)(2) x S-3 symmetry., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Unification of SUSY breaking and GUT breaking
Tatsuo Kobayashi, Yuji Omura, JOURNAL OF HIGH ENERGY PHYSICS, 2, 1, 24, 2015年02月
We build explicit supersymmetric unification models where grand unified gauge symmetry breaking and supersymmetry (SUSY) breaking are caused by the same sector. Besides, the SM-charged particles are also predicted by the symmetry breaking sector, and they give the soft SUSY breaking terms through the so-called gauge mediation. We investigate the mass spectrums in an explicit model with SU(5) and additional gauge groups, and discuss its phenomenological aspects. Especially, nonzero A-term and B-term are generated at one-loop level according to the mediation via the vector superfields, so that the electro-weak symmetry breaking and 125 GeV Higgs mass may be achieved by the large B-term and A-term even if the stop mass is around 1 TeV., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Operator analysis of physical states on magnetized T-2/Z(N) orbifolds
Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto, NUCLEAR PHYSICS B, 890, 442, 480, 2015年01月
We discuss an effective way for analyzing the system on the magnetized twisted orbifolds in operator formalism, especially in the complicated cases T-2/Z(3), T-2/Z(4) and T-2/Z(6). We can obtain the exact and analytical results which can be applicable for any larger values of the quantized magnetic flux M, and show that the (non-diagonalized) kinetic terms are generated via our formalism and the number of the surviving physical states are calculable in a rigorous manner by simply following usual procedures in linear algebra in any case. Our approach is very powerful when we try to examine properties of the physical states on (complicated) magnetized orbifolds T-2/Z(3), T-2/Z(4), T-2/Z(6) (and would be in other cases on higher-dimensional torus) and could be an essential tool for actual realistic model construction based on these geometries. (Note: This article is registered under preprint number: arXiv:1409.5421.) (C) 2014 The Authors. Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Gaussian Froggatt-Nielsen mechanism on magnetized orbifolds
Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Yoshiyuki Tatsuta, PHYSICAL REVIEW D, 90, 10, 2014年11月
We study the structure of Yukawa matrices derived from the supersymmetric Yang-Mills theory on magnetized orbifolds, which can realize the observed quark and charged lepton mass ratios as well as the Cabibbo-Kobayashi-Maswaka (CKM) mixing angles, even with a small number of tunable parameters and without any critical fine-tuning. As a reason behind this, we find that the obtained Yukawa matrices possess a Froggatt-Nielsen-like structure with Gaussian hierarchies, which provides a suitable texture for them favored by the experimental data., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Revisiting Discrete Dark Matter Model:θ_{13}\neq0 and ν_{R} Dark Matter
Yuta Hamada, Tatsuo Kobayashi, Atsushi Ogasahara, Yuji Omura, Fumihiro Takayama, Daiki Yasuhara, JHEP10(2014)183, 10, 2014年10月
We revisit the discrete dark matter model with $A_4$ flavor symmetry

originally introduced by M.Hirsch {\it et.al}. We show that radiative

corrections can lead to non-zero $\theta_{13}$ and non-zero mass for the

lightest neutrino. We find an interesting relation among neutrino mixing

parameters and it indicates the sizable deviation of $s_{23}$ from the maximal

angle $s_{23}^2=1/2$ and the degenerate mass spectrum for neutrinos. Also we

study the possibilities that the right-handed neutrino is a dark matter

candidate. Assuming the thermal freeze-out explains observed dark matter

abundance, TeV-scale right-handed neutrino and flavored scalar bosons are

required. In such a case, flavor symmetry plays an important role for the

suppression of lepton flavor violating processes as well as for the stability

of dark matter. We show that this scenario can be viable against currently

existing constraints from collider, low energy experiments and cosmological

observations., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Axion monodromy inflation with multi-natural modulations
Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto, Yuya Yamaguchi, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 10, 2014年10月
We study parameter space in the axion monodromy inflation corrected by nautically generated terms involving with the axion. The potential has the linear term with multiple sinusoidal functions, which play a role in generating modulations. We show that this potential leads both to a large tensor-to-scalar ratio r(T) similar to 0.16 and to a large negative running of spectral index alpha(s) similar to -(0.02 - 0.03), ameliorating the tension between the result of the PLANCK and that of the BICEP2. To realize these results, a small hierarchy among dynamical scales is required whereas the decay constants in sinusoidal functions remain sub-Planckian in this model. We discuss also reheating process after the inflation in a bottom-up approach., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Axion monodromy inflation with sinusoidal corrections
Tatsuo Kobayashi, Osamu Seto, Yuya Yamaguchi, PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, 10, 2014年10月
We study the axion monodromy inflation with a non-perturbatively generated sinusoidal term. The potential form is a mixture between the natural inflation and the axion monodromy inflation potentials. The sinusoidal term is subdominant in the potential, but leaves significant effects on the resultant fluctuation generated during inflation. A larger tensor-to-scalar ratio can be obtained in our model. We study two scenarios, the single inflation scenario and the double inflation scenario. In the first scenario, the axion monodromy inflation with a sufficient number of e-folds generates a larger tensor-to-scalar ratio of about 0.1-0.15 but also a tiny running of the spectral index. In the second scenario of double inflation, axion monodromy inflation is its first stage, and we assume another inflation follows. In this case, our model can realize a larger tensor-to-scalar ratio and a large negative running of the spectral index simultaneously., OXFORD UNIV PRESS INC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Gauge origin of discrete flavor symmetries in heterotic orbifolds
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino, PHYSICS LETTERS B, 736, 433, 437, 2014年09月
We show that non-Abelian discrete symmetries in orbifold string models have a gauge origin. This can be understood when looking at the vicinity of a symmetry enhanced point in moduli space. At such an enhanced point, orbifold fixed points are characterized by an enhanced gauge symmetry. This gauge symmetry can be broken to a discrete subgroup by a nontrivial vacuum expectation value of the Kahler modulus T. Using this mechanism it is shown that the Delta (54) non-Abelian discrete symmetry group originates from a SU(3) gauge symmetry, whereas the D-4 symmetry group is obtained from a SU(2) gauge symmetry. (C) 2014 The Authors. Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

21pSF-4 Dブレーン模型のゲージ結合定数と模型の制限(21pSF ,素粒子論領域)
上村 尚平, 小林 達夫, 濱田 雄太, 日本物理学会講演概要集, 69, 2, 16, 16, 2014年08月22日
一般社団法人日本物理学会, 日本語

Non-Abelian discrete flavor symmetries of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta, JOURNAL OF HIGH ENERGY PHYSICS, 6, 2014年06月
We study discrete flavor symmetries of the models based on a ten-dimensional supersymmetric Yang-Mills (10D SYM) theory compactified on magnetized tori. We assume non-vanishing non-factorizable fluxes as well as the orbifold projections. These setups allow model-building with more various flavor structures. Indeed, we show that there exist various classes of non-Abelian discrete flavor symmetries. In particular, we find that S-3 flavor symmetries can be realized in the framework of the magnetized 10D SYM theory for the first time., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Flavor structure in D-brane models: Majorana neutrino masses
Yuta Hamada, Tatsuo Kobayashi, Shohei Uemura, JOURNAL OF HIGH ENERGY PHYSICS, 5, 2014年05月
We study the flavor structure in intersecting D-brane models. We study anomalies of the discrete flavor symmetries. We analyze the Majorana neutrino masses, which can be generated by D-brane instanton effects. It is found that a certain pattern of mass matrix is obtained and the cyclic permutation symmetry remains unbroken. As a result, trimaximal mixing matrix can be realized if Dirac neutrino mass and charged lepton mass matrices are diagonal., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Polynomial inflation models after BICEP2
Tatsuo Kobayashi, Osamu Seto, PHYSICAL REVIEW D, 89, 10, 2014年05月
Large field inflation models are favored by the recent BICEP2 that has detected gravitational wave modes generated during inflation. We study general large field inflation models for which the potential contains (constant) quadratic and quartic terms of inflaton field. We show, in this framework, those inflation models can generate the fluctuation with the tensor-to-scalar ratio of 0.2 as well as the scalar spectral index of 0.96; those are very close to the center value of the tensor-to- scalar ratio reported by BICEP2 as well as Planck. Finally, we briefly discuss the particle physics model building of inflation., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Flavor landscape of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta, JOURNAL OF HIGH ENERGY PHYSICS, 4, 2014年04月
We study the flavor landscape of the visible sector of particle physics models based on a ten-dimensional super Yang-Mills theory compactified on magnetized tori preserving four-dimensional Nu = 1 supersymmetry. Recently, we constructed a semirealistic model which contains the minimal supersymmetric standard model (MSSM) using an ansatz of magnetic fluxes and orbifolding projections. However, we can consider more various configurations of magnetic fluxes and orbifolding projections preserving fourdimensional N = 1 supersymmetry. We research systematically such possibilities for leading to MSSM-like models and study their phenomenological aspects., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

28pSB-4 現実的なDブレーンモデルにおける非摂動効果とその現象論的側面(28pSB 余剰次元,素粒子論領域)
上村 尚平, 小林 達夫, 濱田 雄太, 日本物理学会講演概要集, 69, 1, 12, 12, 2014年03月05日
一般社団法人日本物理学会, 日本語

磁化余剰次元からのYukawa結合のガウス構造
安倍博之, 小林達夫, 大木洋, 角田慶吾, 龍田佳幸, 日本物理学会講演概要集, 69, 1, 13, 13, 2014年03月05日
一般社団法人日本物理学会, 日本語

演算子形式での磁場を伴うZ_Nねじれオービフォールド
阿部智大, 藤本教寛, 小林達夫, 三浦貴司, 西脇健二, 坂本眞人, 日本物理学会講演概要集, 69, 1, 12, 12, 2014年03月05日
一般社団法人日本物理学会, 日本語

実現的なDブレーンモデルにおける非摂動効果とその現象論的側面
上村尚平, 小林達夫, 濱田雄太, 日本物理学会講演概要集, 69, 1, 12, 2014年03月05日
日本語

モジュライインフレーションでの大域的磁場生成並びに曲率揺らぎの非ガウス性とテンソル/スカラー比
馬塲一晴, 小林達夫, 瀬戸治, 日本物理学会講演概要集, 69, 1, 124, 124, 2014年03月05日
一般社団法人日本物理学会, 日本語

Discrete R-symmetries and anomaly universality in heterotic orbifolds
Nana G. Cabo Bizet, Tatsuo Kobayashi, Damian K. Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala, JOURNAL OF HIGH ENERGY PHYSICS, 2, 2014年02月
We study discrete R-symmetries, which appear in the 4D low energy effective field theory derived from heterotic orbifold models. We derive the R-symmetries directly from the geometrical symmetries of the orbifolds. In particular, we obtain the corresponding R-charges by requiring that the couplings be invariant under these symmetries. This allows for a more general treatment than the explicit computations of correlation functions made previously by the authors, including models with discrete Wilson lines, and orbifold symmetries beyond plane-by-plane rotational invariance. The R-charges obtained in this manner differ from those derived in earlier explicit computations. We study the anomalies associated with these R-symmetries, and comment on the results., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Z (N) twisted orbifold models with magnetic flux
Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto, JOURNAL OF HIGH ENERGY PHYSICS, 1, 2014年01月
We propose new backgrounds of extra dimensions to lead to four-dimensional chiral models with three generations of matter fermions, that is T (2) /Z (N) twisted orbifolds with magnetic fluxes. We consider gauge theory on six-dimensional space-time, which contains the T (2) /Z (N) orbifold with magnetic flux, Scherk-Schwarz phases and Wilson line phases. We classify all the possible Scherk-Schwarz and Wilson line phases on T (2) /Z (N) orbifolds with magnetic fluxes. The behavior of zero modes is studied. We derive the number of zero modes for each eigenvalue of the Z (N) twist, showing explicitly examples of wave functions. We also investigate Kaluza-Klein mode functions and mass spectra., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Three-generation asymmetric orbifold models from heterotic string theory
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino, JOURNAL OF HIGH ENERGY PHYSICS, 1, 2014年01月
Using Z(3) asymmetric orbifolds in heterotic string theory, we construct N = 1 SUSY three-generation models with the standard model gauge group SU(3)(C) x SU(2)(L) x U(1)(Y) and the left-right symmetric group SU(3)(C) x SU(2)(L) x SU(2)(R) x U(1)(B-L). One of the models possesses a gauge flavor symmetry for the Z(3) twisted matter., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

More on cosmological constraints on spontaneous R-symmetry breaking models
Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 1, 2014年01月
We study the spontaneous R-symmetry breaking model and investigate the cosmological constraints on this model due to the pseudo Nambu-Goldstone boson, R-axion. We consider the R-axion which has relatively heavy mass in order to complement our previous work. In this regime, model parameters, R-axions mass and R-symmetry breaking scale, are constrained by Big Bang Nucleosynthesis and overproduction of the gravitino produced from R-axion decay and thermal plasma. We find that the allowed parameter space is very small for high reheating temperature. For low reheating temperature, the U(1)(R) breaking scale f(a) is constrained as f(a) < 10(12-14) GeV regardless of the value of R-axion mass., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

CKM matrix and flavor symmetries
Takeshi Araki, Hiroyuki Ishida, Hajime Ishimori, Tatsuo Kobayashi, Atsushi Ogasahara, PHYSICAL REVIEW D, 88, 9, 2013年11月
Following the way proposed recently by Hernandez and Smirnov, we seek possible residual symmetries in the quark sector with a focus on the von Dyck groups. We begin with two extreme cases in which both theta(13) and theta(23) or only theta(13) are set to zero. Then, cases where all the Cabibbo-Kobayashi-Maskawa parameters are allowed to take nonzero values are explored. The Z(7) symmetry is favorable to realize only the Cabibbo angle. On the other hand, larger groups are necessary in order to be consistent with all the mixing parameters. Possibilities of embedding the obtained residual symmetries into the Delta(6N(2)) series are also briefly discussed., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Gauge symmetries in heterotic asymmetric orbifolds
Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino, NUCLEAR PHYSICS B, 875, 3, 599, 620, 2013年10月
We study heterotic asymmetric orbifold models. By utilizing the lattice engineering technique, we classify (22,6)-dimensional Narain lattices with right-moving non-Abelian group factors which can be starting points for Z(3) asymmetric orbifold construction. We also calculate gauge symmetry breaking patterns. (C) 2013 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

20aSF-9 Non-Abelian discrete flavor symmetry from magnetized extra dimensions
安倍 博之, 小林 達夫, 大木 洋, 角田 慶吾, 龍田 佳幸, 日本物理学会講演概要集, 68, 2, 1, 1, 2013年08月26日
一般社団法人日本物理学会, 日本語

磁化余剰次元からの非Abel離散フレーバ対称性
安倍博之, 小林達夫, 大木洋, 角田慶吾, 龍田佳幸, 日本物理学会講演概要集, 68, 2, 1, 1, 2013年08月26日
一般社団法人日本物理学会, 日本語

有限群と素粒子物理学 (特集 群と物理学 : 代数構造を用いて物理を知るために)
小林 達夫, 数理科学, 51, 7, 51, 56, 2013年07月
サイエンス社, 日本語

群と物理学 有限群と素粒子物理学
小林達夫, 数理科学, 51, 7, 51, 56, 2013年07月01日
サイエンス社, 日本語

R-charge conservation and more in factorizable and non-factorizable orbifolds
Nana G. Cabo Bizet, Tatsuo Kobayashi, Damian K. Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala, JOURNAL OF HIGH ENERGY PHYSICS, 5, 2013年05月
We consider the string theory origin of R-charge conservation laws in heterotic orbifold compactifications, deriving the corresponding string coupling selection rule for factorizable and non-factorizable orbifolds, with prime ordered and non-prime ordered point groups. R-charge conservation arises due to symmetries among the worldsheet instantons that can mediate the couplings. Among our results is a previously missed non-trivial contribution to the conserved R-charges from the gamma-phases in non-prime orbifolds, which weakens the R-charge selection rule. Symmetries among the worldsheet instantons can also lead to additional selection rules for some couplings. We make a similar analysis for Rule 4 or the "torus lattice selection rule". Moreover, we identify a new string selection rule, that we call Rule 6 or the "coset vector selection rule"., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenological aspects of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Akane Oikawa, Keigo Sumita, NUCLEAR PHYSICS B, 870, 1, 30, 54, 2013年05月
We present a particle physics model based on a ten-dimensional (10D) super Yang-Mills (SYM) theory compactified on magnetized tori preserving four-dimensional N = 1 supersymmetry. The low-energy spectrum contains the minimal supersymmetric standard model with hierarchical Yukawa couplings caused by a wavefunction localization of the chiral matter fields due to the existence of magnetic fluxes, allowing a semi-realistic pattern of the quark and the lepton masses and mixings. We show supersymmetric flavor structures at low energies induced by a moduli-mediated and an anomaly-mediated supersymmetry breaking. (C) 2013 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Cosmic R-string in thermal history
Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi, JOURNAL OF HIGH ENERGY PHYSICS, 5, 2013年05月
We study stabilization of an unstable cosmic string associated with spontaneously broken U(1)(R) symmetry, which otherwise causes a dangerous roll-over process. We demonstrate that in a gauge mediation model, messengers can receive enough corrections from the thermal plasma of the supersymmetric standard model particles to stabilize the unstable modes of the string., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Shifted orbifold models with magnetic flux
Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto, Physical Review D - Particles, Fields, Gravitation and Cosmology, 87, 8, 2013年04月08日
We propose a mechanism to obtain the generation of matter in the standard model. We start from the analysis of the T2/ZN shifted orbifold with magnetic flux, which imposes a ZN symmetry on torus. We also consider several orbifolds such as (T2×T2)/ZN, (T2×T2×T2)/ (ZN×ZN') and (T2×T2×T2)/(Z N×ZN'×ZN'). On such orbifolds, we study the behavior of fermions in two different means - the operator formalism and the explicit analysis of wave functions. For an interesting result, it is found that the number of zero-mode fermions is related to N of the ZN symmetry. In other words, the generation of matter relates to the type of orbifolds. Moreover, we find that shifted orbifold models are severely restricted from realizing three generations. For example, the three-generation model on the type of M4×(T2×T2)/ZN is unique. One can also construct other types of three-generation orbifold models with rich flavor structure. Those results may bring us a realistic model with desired Yukawa structure. © 2013 American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Instability of colliding metastable strings
Takashi Hiramatsu, Minoru Eto, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi, 2013年04月02日
The breaking of $U(1)_R$ symmetry plays a crucial role in modeling the

breaking of supersymmetry (SUSY). In the models that possess both SUSY

preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes,

whose surfaces are constituted by domain walls interpolating a false and a true

vacuum with some winding numbers, can exist. Their (in)stability can strongly

constrain SUSY breaking models theirselves. In the present study, we

investigate the dynamical (in)stability of two colliding metastable tube-like

strings by field-theoretic simulations. From them, we find that the strings

become unstable, depending on the relative collision angle and speed of two

strings, and the false vacuum is eventually filled out by the true vacuum owing

to rapid expansion of the strings or unstable bubbles created as remnants of

the collision., 機関テクニカルレポート，技術報告書，プレプリント等

27aRA-7 Three generations on shifted orbifold with magnetic flux
藤本 教寛, 三浦 貴司, 坂本 眞人, 小林 達夫, 西脇 健二, 日本物理学会講演概要集, 68, 1, 7, 7, 2013年03月26日
一般社団法人日本物理学会, 日本語

27aRA-5 Flavor landscape of 10D SYM theory with general magnetic fluxes
安倍 博之, 小林 達夫, 角田 慶吾, 龍田 佳幸, 日本物理学会講演概要集, 68, 1, 6, 6, 2013年03月26日
一般社団法人日本物理学会, 日本語

一般的な磁気フラックスによる10D SYM理論のフレーバー展望
安倍博之, 小林達夫, 角田慶吾, 龍田佳幸, 日本物理学会講演概要集, 68, 1, 6, 2013年03月05日
日本語

磁気フラックスがあるシフトされたオービフォールドにおける3世代
藤本教寛, 三浦貴司, 坂本眞人, 小林達夫, 西脇健二, 日本物理学会講演概要集, 68, 1, 7, 2013年03月05日
日本語

Cosmic R-string, R-tube and vacuum instability
Minoru Eto, Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi, JOURNAL OF HIGH ENERGY PHYSICS, 3, 2013年03月
We show that a cosmic string associated with spontaneous U(1)(R) symmetry breaking gives a constraint for supersymmetric model building. In some models, the string can be viewed as a tube-like domain wall with a winding number interpolating a false vacuum and a true vacuum. Such string causes inhomogeneous decay of the false vacuum to the true vacuum via rapid expansion of the radius of the tube and hence its formation would be inconsistent with the present Universe. However, we demonstrate that there exist metastable solutions which do not expand rapidly. Furthermore, when the true vacua are degenerate, the structure inside the tube becomes involved. As an example, we show a "bamboo"-like solution, which suggests a possibility observing an information of true vacua from outside of the tube through the shape and the tension of the tube., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

TeV scale mirage mediation in NMSSM
Tatsuo Kobayashi, Hiroki Makino, Ken-Ichi Okumura, Takashi Shimomura, Tsubasa Takahashi, Journal of High Energy Physics, 2013, 1, 2013年
We study the next-to-minimal supersymmetric standard model. We consider soft supersymmetry breaking parameters, which are induced by the mirage mediation mechanism of supersymmetry breaking. We concentrate on the mirage mediation, where the so-called mirage scale is the TeV scale. In this scenario, we can realize the up-type Higgs soft mass of O(200) GeV, while other masses such as gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation between the effective μ-term and the down-type Higgs soft mass ameliorates the fine-tuning in the electroweak symmetry breaking even for μ =O(500) GeV. The mixingbetween the doublet and singlet Higgsbosons issuppressed by (κ/λ) tan-1 β. Then the lightest doublet Higgs mass naturally reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino are light and their linear combination is the lightest superparticle. © 2013 SISSA, Trieste, Italy., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

TeV scale mirage mediation in NMSSM
Tatsuo Kobayashi, Hiroki Makino, Ken-Ichi Okumura, Takashi Shimomura, Tsubasa Takahashi, Journal of High Energy Physics, 2013, 1, 2013年
We study the next-to-minimal supersymmetric standard model. We consider soft supersymmetry breaking parameters, which are induced by the mirage mediation mechanism of supersymmetry breaking. We concentrate on the mirage mediation, where the so-called mirage scale is the TeV scale. In this scenario, we can realize the up-type Higgs soft mass of O(200) GeV, while other masses such as gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation between the effective μ-term and the down-type Higgs soft mass ameliorates the fine-tuning in the electroweak symmetry breaking even for μ =O(500) GeV. The mixingbetween the doublet and singlet Higgsbosons issuppressed by (κ/λ) tan-1 β. Then the lightest doublet Higgs mass naturally reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino are light and their linear combination is the lightest superparticle. © 2013 SISSA, Trieste, Italy., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Cosmological constraints on spontaneous R-symmetry breaking models
Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi, JCAP 1304 (2013) 043, 2012年11月24日
We study general constraints on spontaneous R-symmetry breaking models coming

from the cosmological effects of the pseudo Nambu-Goldstone bosons, R-axions.

They are substantially produced in the early Universe and may cause several

cosmological problems. We focus on relatively long-lived R-axions and find that

in a wide range of parameter space, models are severely constrained. In

particular, R-axions with mass less than 1 MeV are generally ruled out for

relatively high reheating temperature, $T_R>10$ GeV., 機関テクニカルレポート，技術報告書，プレプリント等

Runaway, D term and R-symmetry breaking
Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka, PHYSICAL REVIEW D, 86, 9, 2012年11月
We study the D-term effect on runaway directions of the F-term scalar potential. A minimal renormalizable model is presented where supersymmetry is broken without any pseudomoduli. The model is applied to the hidden sector of gauge mediation for spontaneously breaking R symmetry and generating nonvanishing gaugino masses at the one-loop order., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Massive modes in magnetized brane models
Yuta Hamada, Tatsuo Kobayashi, Progress of Theoretical Physics, 128, 5, 903, 923, 2012年11月
We study higher dimensional models with magnetic fluxes, which can be derived from superstring theory. We study mass spectrum and wavefunctions of massless and massive modes for spinor, scalar and vector fields. We compute the 3-point couplings and higher order couplings among massless modes and massive modes in 4D low-energy effective field theory. These couplings have non-trivial behaviors, because wavefunctions of massless and massive modes are non-trivial. Copyright © Progress of Theoretical Physics 2012., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Superfield description of 10D SYM theory with magnetized extra dimensions
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, NUCLEAR PHYSICS B, 863, 1, 1, 18, 2012年10月
We present a four-dimensional (4D) N = 1 superfield description of supersymmetric Yang-Mills (SYM) theory in ten-dimensional (10D) spacetime with certain magnetic fluxes in compactified extra dimensions preserving partial N = 1 supersymmetry out of full N = 4. We derive a 41) effective action in N = 1 superspace directly from the 10D superfield action via dimensional reduction, and identify its dependence on dilaton and geometric moduli superfields. A concrete model for three generations of quark and lepton superfields are also shown. Our formulation would be useful for building various phenomenological models based on magnetized SYM theories or D-branes. (C) 2012 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Constraining the Higgs sector from false vacua in the next-to-minimal supersymmetric standard model
Tatsuo Kobayashi, Takashi Shimomura, Tsubasa Takahashi, PHYSICAL REVIEW D, 86, 1, 2012年07月
We study the mass, the mixing, and the coupling with the Z boson of the lightest Higgs boson in the next- to-minimal supersymmetric standard model with the Z(3) symmetry. The vacuum structure of the Higgs potential is analyzed, and the new false vacua are discussed. The significant parameter region can be excluded by requiring the realistic vacuum to be deeper than false vacua. In numerical analysis, we also require the couplings to be perturbative up to the Grand Unified Theory scale. Our analysis results in constraints on the properties of the lightest Higgs boson., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Lepton flavor models with discrete values of theta(13)
Hajime Ishimori, Tatsuo Kobayashi, PHYSICAL REVIEW D, 85, 12, 2012年06月
We study the lepton flavor models with the flavor symmetry (Z(N) x Z(N) x Z(N))xZ(3). Our models lead nonvanishing discrete values of theta(13) as well as (12) and theta(23) depending on N. For certain values, our models realize the tribimaximal mixing angles with theta(13) = 0. For other values, our models provide discrete deviation from the tribimaximal mixing angles., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Revisiting coupling selection rules in heterotic orbifold models
Tatsuo Kobayashi, Susha L. Parameswaran, Saul Ramos-Sanchez, Ivonne Zavala, JOURNAL OF HIGH ENERGY PHYSICS, 5, 2012年05月
We study L-point couplings between twisted sector fields in heterotic orbifold compactifications, using conformal field theory. Selection rules provide an easy way to identify which couplings are non-vanishing. Those used in the current literature are gauge invariance, R-charge conservation and the space group selection rule, but they are not the whole story. We revive and refine a fourth selection rule, due to symmetries in the underlying torus lattice, and introduce a fifth one, due to the existence or not of classical worldsheet instanton solutions to mediate the couplings. We consider briefly the phenomenological consequences of the additional rules, in particular for recent orbifold constructions whose field content correspond to that of the MSSM. The structure of the exotic mass matrices is unaltered and many dimension-5 proton-decay operators vanish., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

24pGA-13 Low-energy analysis of magnetized SYM
安倍 博之, 及川 茜, 大木 洋, 小林 達夫, 角田 慶吾, 日本物理学会講演概要集, 67, 1, 9, 9, 2012年03月05日
一般社団法人日本物理学会, 日本語

24pGA-12 磁場とウィルソンラインを用いた高次元模型におけるクォーク・レプトン質量行列の解析(24pGA 余剰次元,素粒子論領域)
安倍 博之, 及川 茜, 大木 洋, 小林 達夫, 角田 慶吾, 野本 優樹, 日本物理学会講演概要集, 67, 1, 9, 9, 2012年03月05日
一般社団法人日本物理学会, 日本語

磁化SYMの低エネルギー解析
安倍博之, 及川茜, 大木洋, 小林達夫, 角田慶吾, 日本物理学会講演概要集, 67, 1, 9, 9, 2012年03月05日
一般社団法人日本物理学会, 日本語

磁場とウィルソンラインを用いた高次元模型におけるクォーク・レプトン質量行列の解析
安倍博之, 及川茜, 大木洋, 小林達夫, 角田慶吾, 野本優樹, 日本物理学会講演概要集, 67, 1, 9, 9, 2012年03月05日
一般社団法人日本物理学会, 日本語

Constraints from unrealistic vacua in the next-to-minimal supersymmetric standard model
Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Osamu Seto, Takashi Shimomura, Progress of Theoretical Physics, 126, 6, 1051, 1076, 2011年12月
We study constraints to avoid deep unrealistic minima in the next-to-minimal supersymmetric standard model. We analyze the scalar potential along directions where all of and one of the three Higgs fields develop their vacuum expectation values, and find unrealistic minima deeper than the electroweak symmetry breaking (EWSB) vacuum. These unrealistic minima threaten the realization of successful EWSB and therefore should be avoided. Necessary conditions for avoiding these minima result in constraints on parameters. We show that a wide and significant region of the parameter space, especially a large λ, is ruled out by our constraints., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Towards minimal S-4 lepton flavor model
Hajime Ishimori, Tatsuo Kobayashi, JOURNAL OF HIGH ENERGY PHYSICS, 10, 2011年10月
We study lepton flavor models with the S-4 flavor symmetry. We construct simple models with smaller numbers of flavon fields and free parameters, such that we have predictions among lepton masses and mixing angles. The model with a S-4 triplet flavon is not realistic, but we can construct realistic models with two triplet flavons, or one triplet and one doublet flavons., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

NON-ABELIAN DISCRETE FLAVOR SYMMETRIES ON ORBIFOLDS
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, Manabu Sakai, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 26, 23, 4067, 4082, 2011年09月
We study non-Abelian flavor symmetries on orbifolds, S-1/Z(2) and T-2/Z(3). Our extra dimensional models realize D-N, Sigma(2N(2)), Delta(3N(2)) and Delta(6N(2)) including A(4) and S-4. In addition, one can also realize their subgroups such as Q(N), T-7, etc. The S-3 flavor symmetry can be realized on both S-1/Z(2) and T-2/Z(3) orbifolds., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Note on moduli stabilization, supersymmetry breaking, and axiverse
Tetsutaro Higaki, Tatsuo Kobayashi, PHYSICAL REVIEW D, 84, 4, 2011年08月
We study properties of moduli stabilization in the four dimensional N = 1 supergravity theory with heavy moduli and would-be saxion-axion multiplets, including light string-theoretic axions. We give general formulation for the scenario that heavy moduli and saxions are stabilized while axions remain light, assuming that moduli are stabilized near the supersymmetric solution. One can find stable vacuum, i.e. nontachyonic saxions, in the nonsupersymmetric Minkowski vacua. We also discuss the cases where the moduli are coupled to the supersymmetry breaking sector and/or moduli have contributions to supersymmetry breaking. Futhermore, we study the models with axions originating from matterlike fields. Our analysis on moduli stabilization is applicable even if there are not light axion multiplets., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

弦理論における,理論と実験との関係とは 弦理論と現実世界
Kane Gordon, 小林 達夫, パリティ, 26, 8, 22, 29, 2011年08月
丸善, 日本語

D term and gaugino masses in gauge mediation
Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka, 2011年06月15日
We systematically study supersymmetry breaking with non-vanishing F and D

terms. We classify the models into two categories and find that a certain class

of models necessarily has runaway behavior of scalar potential, while the other

needs the Fayet-Iliopoulos term to break supersymmetry. The latter class is

useful to have a simple model of gauge mediation where the vacuum is stable

everywhere and the gaugino mass is generated at the one-loop order., 機関テクニカルレポート，技術報告書，プレプリント等

(Extra)ordinary gauge/anomaly mediation
Tatsuo Kobayashi, Yuichiro Nakai, Manabu Sakai, JOURNAL OF HIGH ENERGY PHYSICS, 6, 2011年06月
We study anomaly mediation models with gauge mediation effects from messengers which have a general renormalizable mass matrix with a supersymmetry-breaking spurion. Our models lead to a rich structure of supersymmetry breaking terms in the visible sector. We derive sum rules among the soft scalar masses for each generation. Our sum rules for the first and second generations are the same as those in general gauge mediation, but the sum rule for the third generation is different because of the top Yukawa coupling. We find the parameter space where the tachyonic slepton problem is solved. We also explore the case in which gauge mediation causes the anomalously small gaugino masses. Since anomaly mediation effects on the gaugino masses exist, we can obtain viable mass spectrum of the visible sector fields., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Constraints from Unrealistic Vacua in NMSSM
Konishi Yasufumi, Kanehata Yoshimi, Kobayashi Tatsuo, Seto Osamu, Shimomura Takashi, 素粒子論研究, 119, 3, C32, 2011年
素粒子論グループ 素粒子論研究 編集部, 英語

Inflation, moduli (de)stabilization and supersymmetry breaking
Tatsuo Kobayashia, Manabu Sakaib, Journal of High Energy Physics, 2011, 4, 2011年
We study the cosmological inflation from the viewpoint of the moduli stabilization. We study the scenario that the superpotential has a large value during the inflation era enough to stabilize moduli, but it is small in the true vacuum. This scenario is discussed by using a simple model, one type of hybrid models. © SISSA 2011., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Constraints from unrealistic vacua in the supersymmetric standard model with neutrino mass operators
Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Takashi Shimomura, PHYSICAL REVIEW D, 82, 7, 2010年10月
We analyze a scalar potential of the minimal supersymmetric standard model (MSSM) with neutrino mass operators along unbounded-from-below and color and/or charged breaking directions. We show necessary conditions to avoid the potential minima which can be deeper than the realistic vacuum. These conditions would constrain more strongly than conditions in the MSSM without taking into account neutrino mass operators and can improve the predictive power of supersymmetric models with neutrino mass operators., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Towards the MSSM from F-theory
Kang-Sin Choi, Tatsuo Kobayashi, PHYSICS LETTERS B, 693, 3, 330, 333, 2010年10月
We study the MSSM in F-theory. Its group is the commutant to a structure group SU(5) x U(1)gamma of a gauge bundle in E(8). The spectrum contains three generations of quarks and leptons plus vectorlike electroweak and colored Higgses. The minimal MSSM Yukawa couplings with matter parity is obtained at the renormalizable level. (c) 2010 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Revisiting superparticle spectra in superconformal flavor models
Tatsuo Kobayashi, Yuichiro Nakai, Ryo Takahashi, JOURNAL OF HIGH ENERGY PHYSICS, 9, 2010年09月
We study superparticle spectra in the superconformal flavor scenario with non-universal gaugino masses. The non-universality of gaugino masses can lead to the wino-like or higgsino-like neutralino LSP. Furthermore, it is shown that the parameter space for the higgsino-like LSP includes the region where the fine-tuning problem can be improved. The degeneracy of soft scalar masses does not drastically change when ratios of gaugino masses are of O(1). The degeneracy of scalar masses for squarks and left-handed sleptons would be good enough to avoid the FCNC problem but that of right-handed slepton masses is weak. However, the overall size of right-handed slepton masses becomes larger when the bino becomes heavier. Thus, that would be favorable to avoid the FCNC problem due to soft scalar masses and A-terms., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

磁場を持つ高次元超対称模型の4次元有効理論について
安倍博之, 大木洋, 久能秀幸, 小林達夫, 阪村豊, 角田慶吾, 日本物理学会講演概要集, 65, 2, 9, 9, 2010年08月18日
一般社団法人日本物理学会, 日本語

Constraints from Color and/or Charge Breaking Minima in the $ν$SSM
Tatsuo Kobayashi, Takashi Shimomura, Phys.Rev.D82:035008,2010, 82, 3, 2010年08月12日
We consider a model where right-handed neutrinos and sneutrinos are

introduced to the minimal supersymmetric standard model. In the scalar

potential of this model, there exist trilinear and quartic terms in scalar

potential that are proportional to Yukawa couplings of neutrinos. Due to these

trilinear and quartic terms, Color and/or Charge Breaking (CCB) and

Unbounded-From-Below (UFB) directions appear along which sneutrinos have a

vacuum expectation value, making the vacuum of the electroweak symmetry

breaking unstable. We analyze scalar potential of this model and derive

necessary conditions for CCB and UFB directions to vanish., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

E (6,7,8) magnetized extra-dimensional models
Kang-Sin Choi, Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Yuichiro Nakai, Hiroshi Ohki, Manabu Sakai, EUROPEAN PHYSICAL JOURNAL C, 67, 1-2, 273, 282, 2010年05月
We study 10D super Yang-Mills theory with the gauge groups E (6), E (7) and E (8). We consider the torus/orbifold compactification with magnetic fluxes and Wilson lines. They lead to 4D interesting models with three families of quarks and leptons, whose profiles in extra dimensions are quasi-localized because of magnetic fluxes., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Δ(54)対称性によるレプトン,スレプトン質量行列
石森一, 岡田寛, 小林達夫, 清水勇介, 谷本盛光, 日本物理学会講演概要集, 65, 1, 7, 7, 2010年03月01日
一般社団法人日本物理学会, 日本語

Flavor structure from magnetic fluxes and non-Abelian Wilson lines
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, 2010年01月12日
We study the flavor structure of 4D effective theories, which are derived

from extra dimensional theories with magnetic fluxes and non-Abelian Wilson

lines. We study zero-mode wavefunctions and compute Yukawa couplings as well as

four-point couplings. In our models, we also discuss non-Abelian discrete

flavor symmetries such as $D_4$, $\Delta(27)$ and $\Delta(54)$., 機関テクニカルレポート，技術報告書，プレプリント等

Non-Abelian Discrete Symmetries in Particle Physics
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yusuke Shimizu, Hiroshi Okada, Morimitsu Tanimoto, PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 183, 1, 163, 2010年
We review pedagogically non-Abelian discrete groups, which play an important role in particle physics. We show group-theoretical aspects for many concrete groups, such as representations and their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discuss them explicitly for S-N, A(N), T', D-N, Q(N), E(2N(2)), Delta(3N(2)), T-7, Sigma(3N(3)), and Delta(6N(2)), which have been applied for model building in particle physics. We also present typical flavor models by using A(4), S-4, and Delta(54) groups. Breaking patterns of discrete groups and decompositions of multiplets are important for applications of the non-Abelian discrete symmetry. We discuss these breaking patterns of the non-Abelian discrete group, which are a powerful tool for model buildings. We also review briefly anomalies of non-Abelian discrete symmetries by using the path integral approach., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Three-generation models from E 8 magnetized extra dimensional theory
Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Hiroshi Ohki, Manabu Sakai, Journal of High Energy Physics, 2010, 5, 2010年
We study 10D super Yang-Mills E 8 theory on the 6D torus compactification with magnetic fluxes. We study systematically the possibilities for realizing 4D supersym-metric standard models with three generations of quarks and leptons. We also study quark mass matrices. © SISSA 2010., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Fine tuning in general gauge mediation
Tatsuo Kobayashi, Yuichiro Nakai, Ryo Takahashi, JOURNAL OF HIGH ENERGY PHYSICS, 1, 2010年01月
We study the fine-tuning problem in the context of general gauge mediation. Numerical analyses toward for relaxing fine-tuning are presented. We analyse the problem in typical three cases of the messenger scale, that is, GUT (2 x 10(16) GeV), intermediate (10(10) GeV), and relatively low energy (10(6) GeV) scales. In each messenger scale, the parameter space reducing the degree of tuning as around 10% is found. Certain ratios among gluino mass, wino mass and soft scalar masses are favorable. It is shown that the favorable region becomes narrow as the messenger scale becomes lower, and tachyonic initial conditions of stop masses at the messenger scale are favored to relax the fine-tuning problem for the relatively low energy messenger scale. Our spectra would also be important from the viewpoint of the mu - B problem., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Magnetic flux, Wilson line, and orbifold
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, PHYSICAL REVIEW D, 80, 12, 2009年12月
We study torus/orbifold models with magnetic flux and Wilson line backgrounds. The number of zero modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Delta(54) flavor model for leptons and sleptons
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto, JOURNAL OF HIGH ENERGY PHYSICS, 12, 2009年12月
We study a Delta(54) x Z(2) flavor model for leptons and sleptons. The tri-bimaximal mixing can be reproduced for arbitrary neutrino masses if certain vacuum alignments of scalar fields are realized. The deviation from the tri-bimaximal mixing of leptons is predicted. The predicted upper bound for sin theta(13) is 0.07. The value of sin theta(23) could be deviated from the maximal mixing considerably while sin theta(12) is hardly deviated from 1/root 3. We also study SUSY breaking terms in the slepton sector. Three families of left-handed and right-handed slepton masses are almost degenerate. Our model leads to smaller values of flavor changing neutral currents than the present experimental bounds., SPRINGER, 英語, 書評論文,書評,文献紹介等

Non-Abelian discrete flavor symmetries from magnetized/intersecting brane models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, NUCLEAR PHYSICS B, 820, 1-2, 317, 333, 2009年10月
We study non-Abelian discrete flavor symmetries, which appear in magnetized brane models. For example, D-4, Delta(27) and Delta(54) flavor symmetries can appear with matter fields in several representations. We also study the orbifold background, where non-Abelian flavor symmetries are broken in a certain way. (C) 2009 Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

オービフォールド化によるΔ(54)フレーバー対称性モデル
石森一, 岡田寛, 小林達夫, 清水勇介, 谷本盛光, 日本物理学会講演概要集, 64, 2, 9, 9, 2009年08月18日
一般社団法人日本物理学会, 日本語

Higher order couplings in magnetized brane models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, JOURNAL OF HIGH ENERGY PHYSICS, 6, 2009年06月
We compute three-point and higher order couplings in magnetized brane models. We show that higher order couplings are written as products of three-point couplings. This behavior is the same as higher order amplitudes by conformal field theory calculations e. g. in intersecting D-brane models., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Three generation magnetized orbifold models
Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, NUCLEAR PHYSICS B, 814, 1-2, 265, 292, 2009年06月
We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N = 1 super-Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Lepton flavor model from Delta(54) symmetry
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto, JOURNAL OF HIGH ENERGY PHYSICS, 4, 2009年04月
We present the lepton flavor model with Delta(54), which appears typically in heterotic string models on the T-2/Z(3) orbifold. Our model reproduces the tri-bimaximal mixing in the parameter region around degenerate neutrino masses or two massless neutrinos. We predict the deviation from the tri-bimaximal mixing by putting the experimental data of neutrino masses in the normal hierarchy of neutrino masses. The upper bound of sin(2)theta(13) is 0.01. There is the strong correlation between theta(23) and theta(13). Unless theta(23) is deviated from the maximal mixing considerably, theta(13) remains to be tiny., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Δ(54)対称性からのレプトンフレーバ模型
石森一, 小林達夫, 岡田寛, 清水勇介, 谷本盛光, 日本物理学会講演概要集, 64, 1, 9, 9, 2009年03月03日
一般社団法人日本物理学会, 日本語

A4レプトンフレーバ対称性からのソフトな超対称性の破れの項
石森一, 小林達夫, 大村雄司, 谷本盛光, 日本物理学会講演概要集, 64, 1, 18, 18, 2009年03月03日
一般社団法人日本物理学会, 日本語

Duality cascade of softly broken supersymmetric theories
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Kazutoshi Ohta, Yuji Omura, Haruhiko Terao, PHYSICAL REVIEW D, 79, 4, 2009年02月
We study the duality cascade of softly broken supersymmetric theories. We investigate the renormalization group (RG) flow of SUSY breaking terms as well as supersymmetric couplings. It is found that the magnitudes of SUSY breaking terms are suppressed in most regimes of the RG flow through the duality cascade. At one stage of cascading, the gaugino mass of the strongly coupled sector and scalar masses converge to certain values, which are determined by the gauge coupling and the gaugino mass of the weakly coupled sector. At the next stage, the strongly and weakly coupled sectors are interchanged with each other. We also show the possibility that cascading would be terminated by the gauge symmetry breaking, which is induced by the so-called B-term., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

(Non-)Abelian discrete anomalies
Takeshi Araki, Tatsuo Kobayashi, Jisuke Kubo, Saul Ramos-Sanchez, Michael Ratz, Patrick K. S. Vaudrevange, NUCLEAR PHYSICS B, 805, 1-2, 124, 147, 2008年12月
We derive anomaly constraints for Abelian and non-Abelian discrete symmetries using the path integral approach. We survey anomalies of discrete symmetries in heterotic orbifolds and find a new relation between such anomalies and the so-called 'anomalous' U(1). (C) 2008 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Flavor symmetry breaking and vacuum alignment on orbifolds
Tatsuo Kobayashi, Yuji Omura, Koichi Yoshioka, PHYSICAL REVIEW D, 78, 11, 2008年12月
Flavor symmetry has been widely studied for figuring out the masses and mixing angles of standard model fermions. In this paper we present a framework for handling flavor symmetry breaking where the symmetry breaking is triggered by boundary conditions of scalar fields in extra-dimensional space. The alignment of scalar expectation values is achieved without referring to any details of scalar potential and its minimization procedure. As applications to non-Abelian discrete flavor symmetries, illustrative lepton mass models are constructed where the S-3 and A(4) flavor symmetries are broken down to the directions leading to the tribimaximal form of lepton mixing and realistic mass patterns., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Magnetized orbifold models
Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Journal of High Energy Physics, 2008, 9, 2008年09月01日
We study (4+2n)-dimensional N=1 super Yang-Mills theory on the orbifold background with non-vanishing magnetic fluxes. In particular, we study zero-modes of spinor fields. The flavor structure of our models is different from one in magnetized torus models, and would be interesting in realistic model building. © 2008 SISSA., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

超対称性の破れのMirage伝達機構とヒッグス粒子
小林 達夫, 奥村 健一, 日本物理學會誌, 63, 8, 603, 611, 2008年08月05日
10次元で定式化される超弦理論を4次元にコンパクト化するとモジュライとよばれる場が現れる.これらは適当な真空期待値に固定される必要があるが,最近になってKKLTと呼ばれる新たな固定シナリオが提案された.ここでは,このシナリオをレビューし,この種のモジュライ固定に伴なって現れる超対称標準理論の特徴的な質量スペクトラムを解説する.特にヒッグスセクターの微調整問題との関連を議論する., 一般社団法人日本物理学会, 日本語

超対称性の破れのMirage伝達機構とヒッグス粒子
小林達夫, 奥村健一, 日本物理学会誌, 63, 8, 603, 611, 2008年08月05日
10次元で定式化される超弦理論を4次元にコンパクト化するとモジュライとよばれる場が現れる.これらは適当な真空期待値に固定される必要があるが,最近になってKKLTと呼ばれる新たな固定シナリオが提案された.ここでは,このシナリオをレビューし,この種のモジュライ固定に伴なって現れる超対称標準理論の特徴的な質量スペクトラムを解説する.特にヒッグスセクターの微調整問題との関連を議論する., 一般社団法人日本物理学会, 日本語

Soft supersymmetry breaking terms from A4 lepton flavor symmetry
Hajime Ishimori, Tatsuo Kobayashi, Yuji Omura, Morimitsu Tanimoto, JHEP 0812:082,2008, 2008年07月29日
We study the supersymmetric model with the A4 lepton flavor symmetry, in

particular soft supersymmetry breaking terms, which are predicted from the A4

lepton flavor symmetry. We evaluate soft slepton masses and A-terms within the

framework of supergravity theory. Constraints due to experiments of flavor

changing neutral current processes are examined., 機関テクニカルレポート，技術報告書，プレプリント等

Nonperturbative moduli superpotential with positive exponents
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto, PHYSICAL REVIEW D, 78, 2, 2008年07月
We study nonperturbative moduli superpotentials with positive exponents, i.e. the form like Ae(aT) with a positive constant a and the modulus T. These effects can be generated, e.g., by D-branes which have negative Ramond-Ramond charge of the lower-dimensional D-brane. The scalar potentials including such terms have quite a rich structure. There are several local minima with different potential energies and a high barrier, whose height is of O(M-p(4)). We discuss their implications from the viewpoints of cosmology and particle phenomenology, e.g. the realization of inflation models, avoiding the overshooting problem. This type of potential would be useful to realize the inflation and low-energy supersymmetry breaking., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Higher order couplings from heterotic orbifold theory
Kang-Sin Choi, Tatsuo Kobayashi, NUCLEAR PHYSICS B, 797, 1-2, 295, 321, 2008年07月
We calculate couplings of arbitrary order from correlation functions among twisted strings, using conformal field theory. Twisted strings arise in heterotic string compactified on orbifolds yielding matter fields in the low energy limit. We calculate completely the classical and the quantum amplitude including normalization, up to a contribution from Kahler potential. The classical action has saddle points which are interpreted as worldsheet instantons described by metastable untwisted strings, formed by twisted strings distributed at certain fixed points. This understanding generalizes the area rule, in the case that the locations of twisted strings do not form a polygon, and provides a general rule for calculating these kinds of instanton corrections. An interpretation of couplings involving linearly combined states is given, which commonly appear in non-prime order orbifolds. The quantum part of the amplitude is given by ratios of gamma functions with order one arguments. (C) 2008 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Soft supersymmetry breaking terms from D(4) x Z(2) lepton flavor symmetry
Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yuji Omura, Ryo Takahashi, Morimitsu Tanimoto, PHYSICAL REVIEW D, 77, 11, 2008年06月
We study the supersymmetric model with D(4) x Z(2) lepton flavor symmetry. We evaluate soft supersymmetry breaking terms, i.e., soft slepton masses and A-terms, which are predicted in the D(4) flavor model. We consider constraints due to experiments of flavor-changing neutral current processes., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

D-4 flavor symmetry for neutrino masses and mixing
Hajime Ishimoria, Tatsuo Kobayashi, Hiroshi Ohki, Yuji Omura, Ryo Takahashi, Morimitsu Tanimoto, PHYSICS LETTERS B, 662, 2, 178, 184, 2008年04月
We present the D-4 x Z(2) flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed. (C) 2008 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dynamically sequestered F-term uplifting in extra dimension
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura, Journal of High Energy Physics, 2008, 4, 2008年04月01日
We study moduli stabilization, the dynamical supersymmetry (SUSY) breaking, the uplifting of SUSY anti-de Sitter (AdS) vacuum and the sequestering of hidden sector in a five-dimensional supergravity model, where all modes of the visible sector and the hidden sector are originated from bulk fields. We clarify couplings between the visible and hidden sectors. The expressions for the visible sector soft SUSY breaking terms as well as the hidden sector potential are shown explicitly in our model. The sequestering is achieved dynamically by a wavefunction localization in extra dimension. We find that the tree-level soft scalar mass and the A-term can be suppressed at a SUSY breaking Minkowski minimum where the radius modulus is stabilized, while gaugino masses would be a mirage type., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

SUSYにおけるD4フレーバー対称性
石森一, 小林達夫, 大木洋, 大村雄司, 高橋亮, 谷本盛光, 日本物理学会講演概要集, 63, 1, 10, 10, 2008年02月29日
一般社団法人日本物理学会, 日本語

Metastable supersymmetry breaking vacua from conformal dynamics
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura, Phys.Rev.D77:065001,2008, 2007年12月16日
We study the scenario that conformal dynamics leads to metastable

supersymmetry breaking vacua. At a high energy scale, the superpotential is not

R-symmetric, and has a supersymmetric minimum. However, conformal dynamics

suppresses several operators along renormalization group flow toward the

infrared fixed point. Then we can find an approximately R-symmetric

superpotential, which has a metastable supersymmetry breaking vacuum, and the

supersymmetric vacuum moves far away from the metastable supersymmetry breaking

vacuum. We show a 4D simple model. Furthermore, we can construct 5D models with

the same behavior, because of the AdS/CFT dual., 機関テクニカルレポート，技術報告書，プレプリント等

More about f-term uplifting
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, PHYSICAL REVIEW D, 76, 10, 2007年11月
We study moduli stabilization and a realization of de Sitter vacua in generalized F-term uplifting scenarios of the Kachru-Kallosh-Linde-Trivedi-type anti-de Sitter vacuum, where the uplifting sector X directly couples to the light Kahler modulus T in the superpotential through, e.g., stringy instanton effects. F-term uplifting can be achieved by a spontaneous supersymmetry breaking sector, e.g., the Polonyi model, the O'Raifeartaigh model, and the Intriligator-Seiberg-Shih model. Several models with the X-T mixing are examined, and qualitative features in most models even with such mixing are almost the same as those in the Kachru-Kallosh-Linde-Trivedi scenario. One of the quantitative changes, which are relevant to the phenomenology, is a larger hierarchy between the modulus mass m(T) and the gravitino mass m(3/2), i.e., m(T)/m(3/2)=O(a(2)), where a similar to 4 pi(2). In spite of such a large mass, the modulus F term is suppressed not like F-T=O(m(3/2)/a(2)), but like F-T=O(m(3/2)/a) for ln(M-Pl/m(3/2))similar to a, because of an enhancement factor coming from the X-T mixing. Then we typically find a mirage-mediation pattern of gaugino masses of O(m(3/2)/a), while the scalar masses would be generically of O(m(3/2))., AMER PHYSICAL SOC, 英語, 書評論文,書評,文献紹介等

Discrete R-symmetry anomalies in heterotic orbifold models
Takeshi Araki, Kang-Sin Choi, Tatsuo Kobayashi, Jisuke Kubo, Hiroshi Ohki, PHYSICAL REVIEW D, 76, 6, 2007年09月
Anomalies of discrete R symmetries appearing in heterotic orbifold models are studied. We find that the mixed anomalies for different gauge groups satisfy the universal Green-Schwarz condition, indicating that these anomalies are canceled by the Green-Schwarz mechanism. An exact relation between the anomaly coefficients of the discrete R symmetries and one-loop beta-function coefficients is obtained. We also find that the discrete R symmetries have a good chance to be unbroken down to the supersymmetry breaking scale. Even below this scale a Z(2) subgroup is unbroken, and it may be an origin of the R parity of the minimal supersymmetric standard model. Relations between the R-symmetry anomalies and T-duality anomalies are also investigated., AMER PHYSICAL SOC, 英語, 書評論文,書評,文献紹介等

TeV scale partial mirage unification and neutralino dark matter
Hiroyuki Abe, Yeong Gyun Kim, Tatsuo Kobayashi, Yasuhiro Shimizu, Journal of High Energy Physics, 2007, 9, 2007年09月01日
We study the TeV scale partial mirage unification scenario, where the gluino and wino masses are degenerate around a TeV scale, but the bino mass is not degenerate. This scenario has phenomenologically interesting aspects. First, because of the degeneracy between the gluino and wino masses, this scenario does not have the little hierarchy problem, that is, the higgisino mass is around 150 GeV. The lightest superparticle is a mixture of the bino and higgsino, and can lead to a right amount of thermal relic density as a dark matter candidate. © SISSA 2007., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

String-derived D-4 flavor symmetry and phenomenological implications (vol 76, 035005, 2007)
Pyungwon Ko, Tatsuo Kobayashi, Jae-hyeon Park, Stuart Raby, PHYSICAL REVIEW D, 76, 5, 2007年09月
In this paper we show how some flavor symmetries may be derived from the

heterotic string, when compactified on a 6D orbifold. In the body of the paper

we focus on the $D_4$ family symmetry, recently obtained in $Z_3 \times Z_2$

orbifold constructions. We show how this flavor symmetry constrains fermion

masses, as well as the soft SUSY breaking mass terms. Flavor symmetry breaking

can generate the hierarchy of fermion masses and at the same time the flavor

symmetry suppresses large flavor changing neutral current processes., AMER PHYSICAL SOC, 英語, その他

R-symmetry, supersymmetry breaking and metastable vacua in global and local supersymmetric theories
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura, JHEP 0711:044,2007, 2007年08月23日
We study N=1 global and local supersymmetric theories with a continuous

global $U(1)_R$ symmetry as models of dynamical supersymmetry (SUSY) breaking.

We introduce explicit R-symmetry breaking terms into such models, in particular

a generalized O'Raifeartaigh model. Such explicit R-symmetry breaking terms can

lead to a SUSY preserving minimum. We classify explicit R-symmetry breaking

terms by the structure of newly appeared SUSY stationary points as a

consequence of the R-breaking effect, which could make the SUSY breaking vacuum

metastable. We show that the R-breaking terms are basically divided into two

categories. One of them does not generate a SUSY solution, or yields SUSY

solutions that disappear in the case of supergravity when we tune a parameter

so that the original SUSY breaking minimum becomes a Minkowski vacuum. We also

show that the general argument by Nelson and Seiberg for a dynamical SUSY

breaking still holds with a local SUSY except for a certain nontrivial case,

and present concrete examples of the exception., 機関テクニカルレポート，技術報告書，プレプリント等

Relaxed fine-tuning in models with nonuniversal gaugino masses
Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura, PHYSICAL REVIEW D, 76, 1, 2007年07月
We study, in a bottom-up approach, the fine-tuning problem between soft supersymmetry (SUSY) breaking parameters and the mu term for the successful electroweak symmetry breaking in the minimal supersymmetric standard model. It is shown that certain ratios among nonuniversal gaugino masses at the grand unified theory (GUT) scale are necessary to reduce fine-tuning. In addition, when all the gaugino masses are regarded as independent ones in their origins, a small gluino mass M-3 less than or similar to 120 GeV and a nonvanishing A term A(t)similar to O(M-3) associated with top squarks are also required at the GUT scale as well as the nonuniversality. On the other hand, when we consider some UV theory, which fixes ratios of soft SUSY breaking parameters as certain values aside from the overall magnitude, heavier spectra are allowed. It is favored that the gluino and W-ino masses are almost degenerate at the weak scale, while a wider region of b-ino mass is favorable., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

TeV scale mirage mediation and natural little supersymmetric hierarchy
Kiwoon Choi, Kwang Sik Jeong, Tatsuo Kobayashi, Ken-ichi Okumura, PHYSICAL REVIEW D, 75, 9, 2007年05月
TeV scale mirage mediation has been proposed as a supersymmetry-breaking scheme reducing the fine-tuning for electroweak symmetry breaking in the minimal supersymmetric extension of the standard model. We discuss a moduli stabilization setup for TeV scale mirage mediation which allows an extradimensional interpretation for the origin of supersymmetry breaking and naturally gives a weak-scale size of the Higgs B parameter. The setup utilizes the holomorphic gauge kinetic functions depending on both the heavy dilaton and the light volume modulus whose axion partners are assumed to be periodic fields. We also examine the low-energy phenomenology of TeV scale mirage mediation, particularly the constraints from electroweak symmetry breaking and flavor changing neutral current processes., AMER PHYSICAL SOC, 英語, 書評論文,書評,文献紹介等

Stringy origin of non-Abelian discrete flavor symmetries
Tatsuo Kobayashi, Hans Peter Nilles, Felix Ploeger, Stuart Raby, Michael Ratz, NUCLEAR PHYSICS B, 768, 1-2, 135, 156, 2007年04月
We study the origin of non-Abelian discrete flavor symmetries in superstring theory. We classify all possible non-Abelian discrete flavor symmetries which can appear in heterotic orbifold models. These symmetries include D-4 and Delta(54). We find that the symmetries of the couplings are always larger than the symmetries of the compact space. This is because they are a consequence of the geometry of the orbifold combined with the space group selection rules of the string. We also study possible breaking patterns. Our analysis yields a simple geometric understanding of the realization of non-Abelian flavor symmetries. (c) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Non-factorisable ℤ2 × ℤ2 heterotic orbifold models and Yukawa couplings
Stefan Förste, Tatsuo Kobayashi, Hiroshi Ohki, Kei-Jiro Takahashi, Journal of High Energy Physics, 2007, 3, 2007年03月01日
We classify compactification lattices for supersymmetric 2 × 2 orbifolds. These lattices include factorisable as well as non-factorisable six-tori. Different models lead to different numbers of fixed points/tori. A lower bound on the number of fixed tori per twisted sector is given by four, whereas an upper bound consists of 16 fixed tori per twisted sector. Thus, these models have a variety of generation numbers. For example, in the standard embedding, the smallest number of net generations among these classes of models is equal to six, while the largest number is 48. Conditions for allowed Wilson lines and Yukawa couplings are derived. © SISSA 2007., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Time variation of the proton-electron mass ratio and the fine structure constant with a runaway dilaton
Takeshi Chiba, Tatsuo Kobayashi, Masahide Yamaguchi, Jun'ichi Yokoyama, PHYSICAL REVIEW D, 75, 4, 2007年02月
Recent astrophysical observations indicate that the proton-electron mass ratio and the fine structure constant have gone through nontrivial time evolution. We discuss their time variation in the context of a dilaton runaway scenario with gauge coupling unification at the string scale M-s. We show that the choice of adjustable parameters allows them to fit the same order magnitude of both variations and their (opposite) signs in such a scenario., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Moduli stabilization, F-term uplifting, and soft supersymmetry breaking terms
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura, PHYSICAL REVIEW D, 75, 2, 2007年01月
We study moduli stabilization with F-term uplifting. As a source of uplifting F-term, we consider spontaneous supersymmetry breaking models, e.g. the Polonyi model and the Intriligator-Seiberg-Shih model. We analyze potential minima by requiring almost vanishing vacuum energy and evaluate the size of modulus F-term. We also study soft SUSY-breaking terms. In our scenario, the mirage mediation is dominant in gaugino masses. Scalar masses can be comparable with gaugino masses or much heavier, depending on couplings with spontaneous supersymmetry breaking sector., AMERICAN PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dynamical realization of democratic Yukawa matrices and alignment of A terms
Tatsuo Kobayashi, Yuji Omura, Haruhiko Terao, PHYSICAL REVIEW D, 74, 5, 2006年09月
We study realization of the democratic form of Yukawa matrices by infrared fixed points. We investigate renormalization-group flows of Yukawa couplings in models with a single Yukawa matrix for three families, and up and down-sector Yukawa matrices. It is found that each model has its certain pattern of renormalization-group flows of Yukawa matrices. We apply them to the charged lepton sector and quark sector, and examine in which situation our class of models can lead to realistic results for the mass ratios and mixing angles between the second and third families. We also study corresponding A-terms. The A-terms approach toward the universal form with no physical CP-violating phase. Thus, constraints due to various neutral flavor changing processes except for mu -> e gamma are found to be satisfied by this dynamics. In order to suppress the electric dipole moments as well as mu -> e gamma sufficiently, more alignment of the A-terms with some reason is required., AMERICAN PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Fine-tuning in gauge mediated supersymmetry breaking models and induced top Yukawa coupling
Tatsuo Kobayashi, Haruhiko Terao, Akito Tsuchiya, PHYSICAL REVIEW D, 74, 1, 2006年07月
It is shown that fine-tuning of the Higgs parameters stronger than a few percent is required at best in the models with gauge mediated supersymmetry breaking. With the aim of solving this problem, we consider a new type of models in which the top Yukawa coupling is induced at TeV scale through mass mixing with unknown matter fields. Then it is found that the fine-tuning problem can be eliminated essentially. We discuss some phenomenological features of this model and also consider the extension to the next-to-minimal models., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Moduli-mixing racetrack model
H Abe, T Higaki, T Kobayashi, NUCLEAR PHYSICS B, 742, 187, 207, 2006年05月
We study supersymmetric models with double gaugino condensations in the hidden sector, where the gauge couplings depend on two light moduli of superstring theory. We perform a detailed analysis of this class of model and show that there is no stable supersymmetric minimum with finite vacuum values of moduli fields. Instead, we find that the supersymmetry breaking occurs with moduli stabilized and negative vacuum energy. That yields moduli-dominated soft supersymmetry breaking terms. To realize slightly positive (or vanishing) vacuum energy, we add uplifting potential. We discuss uplifting does not change qualitatively the vacuum expectation values of moduli and the above feature of supersymmetry breaking. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

29pXA-6 超対称標準理論の微調整問題とその解消の試み(素粒子論領域)
小林 達夫, 寺尾 治彦, 土谷 暁人, 日本物理学会講演概要集, 61, 1, 10, 10, 2006年03月04日
一般社団法人日本物理学会, 日本語

Little SUSY hierarchy in mixed modulus-anomaly mediation
K Choi, KS Jeong, T Kobayashi, K Okumura, PHYSICS LETTERS B, 633, 2-3, 355, 361, 2006年02月
Motivated by the KKLT string compactification involving a supersymmetry-breaking uplifting potential, we examine 4D effective supergravity with a generic form of uplifting potential, focusing on the possibility that the resulting mixed modulus-anomaly mediated soft terms realize the little hierarchy between the Higgs boson masses m(H) and the sparticle masses m(SUSY). It is noted that for some type of uplifting potential, the anomaly-mediated contribution to m(H)(2) at M-GUT can cancel the subsequent renormalization group evolution of m(H)(2) down to TeV scale, thereby the model can naturally realize the little hierarchy m(H)(2) similar to m(SUSY)(2)/8 pi(2) which is desirable for the lightest Higgs boson mass to satisfy the experimental bound. In such models, the other Higgs mass parameters mu and B can have the desirable size mu similar to B similar to mH without severe fine-tuning of parameters, although the gravitino is much heavier than the Higgs boson. Those models for the little hierarchy avoid naturally the dangerous SUSY flavor and CP violations, and predict nearly degenerate low energy gaugino masses, pure Higgsino LSP and also a specific relation between the stop and gaugino masses. (c) 2005 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Kachru-Kallosh-Linde-Trivedi-type models with moduli-mixing superpotential
H Abe, T Higaki, T Kobayashi, PHYSICAL REVIEW D, 73, 4, 2006年02月
We study KKLT type models with moduli-mixing superpotential. In several string models, gauge kinetic functions are written as linear combinations of two or more moduli fields. Their gluino condensation generates moduli-mixing superpotential. We assume one of moduli fields is frozen already around the string scale. It is found that Kahler modulus can be stabilized at a realistic value without tuning 3-form fluxes because of gluino condensation on (non-)magnetized D-brane. Furthermore, we do not need to highly tune parameters in order to realize a weak gauge coupling and a large hierarchy between the gravitino mass and the Planck scale, when there exists nonperturbative effects on D3-brane. SUSY breaking patterns in our models have a rich structure. Also, some of our models have cosmologically important implications, e.g., on the overshooting problem and the destabilization problem due to finite temperature effects as well as the gravitino problem and the moduli problem., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Remark on integrating out heavy moduli in flux compactification
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Physical Review D - Particles, Fields, Gravitation and Cosmology, 74, 4, 2006年
We study two steps of moduli stabilization in type IIB flux compactification with gaugino condensations. We consider the condition that one can integrate out heavy moduli first with light moduli remaining. We give appendix, where detail study is carried out for potential minima of the model with a six dimensional compact space with h1,1=h2,1=1, including the model, whose respective moduli with h1,1,h2,1≠1 are identified. © 2006 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

More about soft terms and FCNC in realistic string constructions
Tatsuo Kobayashi, Carlos Mũoz, Journal of High Energy Physics, 1, 1107, 1117, 2006年
In realistic four-dimensional string constructions the presence of anomalous U(1)'s is generic. In addition, the associated Fayet-Iliopoulos contribution to the D-term can break the extra gauge symmetries. As a consequence, physical particles can appear combined with other states. We show that even if a three-generation standard-like model has originally flavour-independent soft scalar masses, the particle mixing contribution may generate non-universality among them. Thus FCNC effects which were apparently absent reappear. We also discuss the size of these contributions in an explicit model, and how they can be suppressed. © SISSA 2006., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Flavor structure and coupling selection rule from intersecting D-branes
T Higaki, N Kitazawa, T Kobayashi, K Takahashi, PHYSICAL REVIEW D, 72, 8, 2005年10月
We study flavor structure and the coupling selection rule in intersecting D-brane configurations on T(2)xT(2)xT(2) as well as its orbifold/orientifold compactifications. We formulate the selection rule for Yukawa couplings and its extensions to generic n-point couplings. We investigate the possible flavor structure, which can appear from intersecting D-brane configuration. Then, we show there is a certain rule among intersecting numbers for states corresponding to allowed Yukawa couplings, and also it is found that their couplings are determined by discrete Abelian symmetries. Our studies on the flavor structure and the coupling selection rule in this class of models show that there is no solution to derive realistic Yukawa matrices only from stringy 3-point couplings at the tree-level within the framework of the minimal matter content of the supersymmetric standard model., AMERICAN PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Induced top-Yukawa coupling and suppressed Higgs mass parameters
T Kobayashi, H Nakano, H Terao, PHYSICAL REVIEW D, 71, 11, 2005年06月
In the scenarios with heavy top squarks, mass parameters of the Higgs field must be fine-tuned due to a large logarithmic correction to the soft scalar mass. We consider a new possibility that the top-Yukawa coupling is small above TeV scale. The large top mass is induced from strong Yukawa interaction of the Higgs with another gauge sector, in which supersymmetry breaking parameters are given to be small. Then it is found that the logarithmic correction to the Higgs soft scalar mass is suppressed in spite of the strong coupling, and the fine-tuning is ameliorated. We propose an explicit model coupled to a superconformal gauge theory which realizes the above situation., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Democratic mass matrices induced by strong gauge dynamics and large mixing angles for leptons
Tatsuo Kobayashi, Hiroaki Shirano, Haruhiko Terao, Progress of Theoretical Physics, 113, 5, 1077, 1099, 2005年05月
We consider the dynamical realization of the democratic type of Yukawa coupling matrices as the Pendelton-Ross infrared fixed points. Such fixed points of the Yukawa couplings become possible through the introduction of many Higgs fields, which are made superheavy, but one massless mode. Explicitly, we consider a strongly coupled supersymmetric GUT based on SU(5) × SU(5), in which rapid convergence to the infrared fixed point generates sufficiently large mass hierarchy for quarks and leptons. In particular, it is found that the remarkable difference between mixing angles in the quark and lepton sectors can be explained as a simple dynamical consequence. We also discuss a possible scenario leading to a realistic mass spectra and mixing angles for quarks and leptons. In this scheme, the Yukawa couplings not only for top but also for bottom appear close to their quasi-fixed points at low energy and, therefore, tan β should be large., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Lepton masses and mixing angles from heterotic orbifold models
P Ko, T Kobayashi, JH Park, PHYSICAL REVIEW D, 71, 9, 2005年05月
We systematically study the possibility for realizing realistic values of lepton mass ratios and mixing angles by using only renormalizable Yukawa couplings derived from the heterotic Z(6)-I orbifold. We assume one pair of up and down sector Higgs fields. We consider both the Dirac neutrino mass scenario and the seesaw scenario with degenerate right-handed majorana neutrino masses. It is found that realistic values of the charged lepton mass ratios, m(e)/m(tau) and m(mu)/m(tau), the neutrino mass squared difference ratio, Delta m(31)(2)/Delta m(21)(2), and the lepton mixing angles can be obtained in certain cases., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa coupling structure in intersecting D-brane models
N Kitazawa, T Kobayashi, N Maru, N Okada, EUROPEAN PHYSICAL JOURNAL C, 40, 4, 579, 587, 2005年04月
The structure of Yukawa coupling matrices is investigated in type IIA T-6/(Z(2) x Z(2)) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T-6 = T-2 x T-2 x T-2. We study the new type of favor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Large mass scale by strong gauge dynamics with infrared fixed point
Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao, Yoshihisa Yamada, Progress of Theoretical Physics, 113, 2, 413, 427, 2005年02月
We consider a mechanism for realizing the desired decoupling of the strongly-coupled sector which is supposed to generate hierarchical structure of the Yukawa couplings. In our mechanism, the same strongly-coupled sector is responsible for generating a sufficiently flat potential and a large vacuum expectation value (VEV) of a gauge-singlet scalar field by suppressing its soft scalar mass and self-coupling. A vacuum instability is caused by a supersymmetry-breaking A-term of order 10 TeV. We explicitly demonstrate the infrared convergence of soft scalar masses due to strongly-coupled dynamics and show that the soft mass of the singlet is at most of the same order as the soft masses of squarks and sleptons, which are much more strongly suppressed than the A-term. The physical mass scale of the decoupling is calculated in a self-consistent way. We also reinterpret the result in terms of an RG-improved effective potential., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

素粒子物理学の進展 強統一とレプトン混合角による民主的質量行列
寺尾治彦, 小林達夫, 白野宏昌, 素粒子論研究, 110, 4, D7-D8, D8, 2005年01月20日
素粒子論グループ 素粒子論研究 編集部, 日本語

Searching for realistic 4d string models with a Pati-Salam symmetry. Orbifold grand unified theories from heterotic string compactification on a Z(6) orbifold
T Kobayashi, S Raby, RJ Zhang, NUCLEAR PHYSICS B, 704, 1-2, 3, 55, 2005年01月
Motivated by orbifold grand unified theories, we construct a class of three-family Pati-Salam models in a Z(6) Abelian symmetric orbifold with two discrete Wilson lines. These models have marked differences from previously-constructed three-family models in prime-order orbifolds. In the limit where one of the six compactified dimensions (which lies in a Z(2) sub-orbifold) is large compared to the string length scale, our models reproduce the supersymmetry and gauge symmetry breaking pattern of 5d orbifold grand unified theories on an S-1/Z(2) orbicircle. We find a horizontal 2 divided by 1 splitting in the chiral matter spectra-2 families of matter are localized on the Z(2) orbifold fixed points. and 1 family propagates in the 5d bulk-and identify them as the first-two and third families. Remarkably. the first two families enjoy a non-Abelian dihedral D-4 family symmetry. due to the geometric setup of the compactified space. In all our models there are always some color triplets. i.e.. (6.1.1) representations of the Pati-Salam group, survive orbifold projections. They could be utilized to spontaneously break the Pati-Salam symmetry to that of the Standard Model. One model. with a 5d E-6 symmetry. may give rise to interesting low energy phenomenology. We study gauge coupling unification. allowed Yukawa couplings and some of their phenomenological consequences. The E-6 model has a renormalizable Yukawa coupling only for the third family. It predicts a gauge-Yukawa unification relation at the 5d compactification scale, and is capable of generating reasonable quark/lepton masses and mixings. Potential problems are also addressed, they may point to the direction for refining our models. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 書評論文,書評,文献紹介等

Radiative stabilization of warped space
Tatsuo Kobayashi, Koichi Yoshioka, JHEP 0411:024,2004, 2004年09月30日
Higher-dimensional field theory has been applied to explore various issues in

recent particle physics such as the gauge hierarchy problem. In order for such

approaches to be viable, a crucial ingredient is to fix the sizes of extra

dimensions at some finite values, which sizes are generically free parameters

in the theory. In this paper, we present several schemes to determine the

radius of extra dimension in warped five-dimensional theory. In every case, a

non-vanishing Fayet-Iliopoulos term for abelian gauge factor plays a crucial

role for the radius stabilization. It is radiatively generated in the presence

of charged matter fields and the compactification is therefore spontaneous, not

forced by selected operators. The low-energy supersymmetry is broken or

unbroken, and the radius can be fixed to give a small or large scale hierarchy

without any fine tuning of parameters. We also discuss a model of the radius

stabilization correlated with Yukawa hierarchy and supersymmetry breaking., 機関テクニカルレポート，技術報告書，プレプリント等

Quark masses and mixing angles in heterotic orbifold models
P Ko, T Kobayashi, JH Park, PHYSICS LETTERS B, 598, 3-4, 263, 272, 2004年09月
We study systematically the possibility for realizing realistic values of quark mass ratios m(c)/m(t) and m(s)/m(b) and the mixing angle V-cb by using only renormalizable Yukawa couplings derived from heterotic orbifold models. We assume one pair of up and down sector Higgs fields. We find many realistic Yukawa matrices. (C) 2004 Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Constructing 5d orbifold grand unified theories from heterotic strings
T Kobayashi, S Raby, RJ Zhang, PHYSICS LETTERS B, 593, 262, 270, 2004年07月
A three-generation Pati-Salam model is constructed by compactifying the heterotic string on a particular T-6/Z(6) Abelian symmetric orbifold with two discrete Wilson lines. The compactified space is taken to be the Lie algebra lattice G(2) circle plus SU(3) circle plus SO(4). When one dimension of the SO(4) lattice is large compared to the string scale, this model reproduces many features of a 5d SO(10) grand unified theory compactified on an S-1/Z(2) orbifold. (Of course, with two large extra dimensions we can obtain a 6d SO(10) grand unified theory.) We identify the orbifold parities and other ingredients of the orbifold grand unified theories in the string model. Our construction provides a UV completion of orbifold grand unified theories, and gives new insights into both field theoretical and string theoretical constructions. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Supersymmetry breaking in warped geometry
K Choi, DY Kim, IW Kim, T Kobayashi, EUROPEAN PHYSICAL JOURNAL C, 35, 2, 267, 275, 2004年06月
We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS(5) which generate the hierarchical Yukawa couplings by dynamically quasi-localizing the bulk matter fields in an extra dimension. Such models can be regarded as the AdS dual of the recently studied 4-dimensional models which contain a supersymmetric CFT to generate the hierarchical Yukawa couplings. In such models, if supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous flavor-violating soft parameters are suppressed with an appropriate correlation with the Yukawa coupling suppression, thereby avoiding the SUSY flavor problem in a natural manner. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework, and discuss the constraints from flavor-changing rare processes. Most of the discussions in this paper can be applied also to models with a flat extra dimension in which the Yukawa hierarchy is generated by quasi-localizing the bulk matter fields in the extra dimension., SPRINGER, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Anomalous U(1) D-term contribution in type I string models
T Higaki, Y Kawamura, T Kobayashi, H Nakano, PHYSICAL REVIEW D, 69, 8, 2004年04月
We study the D-term contribution for anomalous U(1) symmetries in type I string models and derive a general formula for the D-term contribution, assuming that the dominant source of supersymmetry breaking is given by the F terms of the dilaton, (overall) moduli, or twisted moduli fields. On the basis of the formula, we also point out that there are several features different from the case of heterotic string models. The differences originate from the different forms of the Kahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Suppressed supersymmetry breaking terms in the Higgs sector
Tatsuo Kobayashi, Haruhiko Terao, JHEP 0407 (2004) 026, 2004年03月31日
We study the little hierarchy between mass parameters in the Higgs sector and

other SUSY breaking masses. This type of spectrum can relieve the fine-tuning

problem in the MSSM Higgs sector. Our scenario can be realized by

superconformal dynamics. The spectrum in our scenario has significant

implications in other phenomenological aspects like the relic abundance of the

lightest neutralino and relaxation of the unbounded-from-below constraints., 機関テクニカルレポート，技術報告書，プレプリント等

Non-perturbative Kähler potential, dilaton stabilization and Fayet-Iliopoulos term
Tetsutaro Higaki, Yoshiharu Kawamura, Tatsuo Kobayashi, Hiroaki Nakano, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 582, 3-4, 257, 262, 2004年03月04日
We study the dilaton stabilization in models with anomalous U(1) symmetry by adding specific string-motivated, non-perturbative corrections to the tree-level dilaton Kähler potential. We find that the non-perturbative effects can stabilize the dilaton at a desirably large value. We also observe that the size of Fayet-Iliopoulos term is reduced at the stabilized point. © 2004 Published by Elsevier B.V., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

D-term Inflation and Nonperturbative Kahler Potential of Dilaton
Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto, JHEP 0407 (2004) 035, 2004年02月19日
We study the $D$-term inflation scenario with a nonperturbative K\"ahler

potential of the dilaton field. Although the FI term which leads an

inflationary expansion is given by the derivative of the K\"ahler potential

with respect to the dilaton in heterotic string models with anomalous U(1), the

too large magnitude is problematic for a viable $D$-term inflation. In this

paper, we point out that the K\"ahler potential with a nonperturbative term can

reduce the magnitude of FI term to desired values while both the dilaton

stabilization and $D$-term domination in the potential are realized by

nonperturbative superpotential., 機関テクニカルレポート，技術報告書，プレプリント等

Localization of heterotic anomalies on various hypersurfaces of T-6/Z(4)
SG Nibbelink, M Hillenbach, T Kobayashi, MGA Walter, PHYSICAL REVIEW D, 69, 4, 2004年02月
We investigate the structure of local anomalies of heterotic E(8)xE'(8) theory on T-6/Z(4). We show that the untwisted states lead to anomalies in 10, four, and in particular six dimensions. At each of the six dimensional fixed spaces of this orbifold the twisted states ensure, that the anomalies factorize separately. As some of these twisted states live on T-2/Z(2), they give rise to four dimensional anomalies as well. At all four dimensional fixed points at worst a single Abelian anomaly can arise. Additionally we show that the anomalies in all these dimensions factorize in a universal way and can be canceled simultaneously., AMERICAN PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Heterotic Yukawa couplings and Wilson lines
O Lebedev, STRING PHENOMENOLOGY 2003, 256, 259, 2004年
I discuss effects of the Wilson lines on heterotic Yukawa couplings with the focus on their relation to CP violation., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Dilaton and moduli fields in D-term inflation
T Kobayashi, O Seto, PHYSICAL REVIEW D, 69, 2, 2004年01月
We investigate the possibility of D-term inflation within the framework of type-I string-inspired models. Although the D-term inflation model has the excellent property that it is free of the so-called eta problem, two serious problems appear when we embed D-term inflation in string theory: the magnitude of the FI term and the rolling motion of the dilaton. In the present paper, we analyze the potential of D-term inflation in type-I-inspired models and study the behavior of dilaton and twisted moduli fields. Adopting the nonperturbative superpotential induced by gaugino condensation, the twisted moduli can be stabilized. If the dilaton is in a certain range, it evolves very slowly and does not run away to infinity. Thus D-term-dominated vacuum energy becomes available for driving inflation. By studying the density perturbation generated by the inflation model, we derive the constraints on model parameters and give some implications on D-term inflation in type-I-inspired models., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Exact S3 symmetry solving the supersymmetric flavor problem
Tatsuo Kobayashi, Jisuke Kubo, Haruhiko Terao, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 568, 1-2, 83, 91, 2003年08月21日
The exact discrete flavor symmetry, S3 in the hadronic sector and S3 x Z2 in the leptonic sector, which has been recently found, is introduced in a supersymmetric extension of the standard model. We investigate the supersymmetric flavor problem, and explicitly find that thanks to the flavor symmetry the dangerous FCNC processes and CP-violating phases are sufficiently suppressed. © 2003 Elsevier B.V. All rights reserved., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Twisted moduli stabilization in type I string models
T Higaki, T Kobayashi, PHYSICAL REVIEW D, 68, 4, 046006, 2003年08月
We consider a model with dilaton and twisted moduli fields, which is inspired by type I string models. The stabilization of their vacuum expectation values is studied. We find that the stabilization of the twisted moduli field has different aspects from dilaton stabilization., AMER PHYSICAL SOC, 英語

Exact S-3 symmetry solving the supersymmetric flavor problem
T Kobayashi, J Kubo, H Terao, PHYSICS LETTERS B, 568, 1-2, 83, 91, 2003年08月
The exact discrete flavor symmetry, S-3 in the hadronic sector and S-3 x Z(2) in the leptonic sector, which has been recently found, is introduced in a supersymmetric extension of the standard model. We investigate the supersymmetric flavor problem, and explicitly find that thanks to the flavor symmetry the dangerous FCNC processes and CP-violating phases are sufficiently suppressed. (C) 2003 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Flavor violation in supersymmetric theories with gauged flavor symmetries
T Kobayashi, H Nakano, H Terao, K Yoshioka, PROGRESS OF THEORETICAL PHYSICS, 110, 2, 247, 267, 2003年08月
In this paper, we study flavor violation in supersymmetric models with gauged flavor symmetries. There are several sources of flavor violation in these theories. The dominant flavor violation is the tree-level D-term contribution to scalar masses generated by flavor symmetry breaking. We present a new approach for suppressing these phenomenologically dangerous effects by separating the flavor-breaking sector from the supersymmetry-breaking sector. This separation can be achieved either in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor symmetries can yield sizable generation-dependent masses of scalars. Generically the gaugino mass effects are not suppressed, even if the dominant D-term contribution is suppressed. We also analyze the constraints on the flavor symmetry sector resulting from these flavor-violating corrections., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE, 英語, 書評論文,書評,文献紹介等

Heterotic string backgrounds and CP violation
T Kobayashi, O Lebedev, PHYSICS LETTERS B, 565, 1-4, 193, 200, 2003年07月
In the framework of Z(N) orbifolds, we discuss effects of heterotic string backgrounds including discrete Wilson lines on the Yukawa matrices and their connection to CP violation. (C) 2003 Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語

Heterotic Yukawa couplings and continuous Wilson lines
T Kobayashi, O Lebedev, PHYSICS LETTERS B, 566, 1-2, 164, 170, 2003年07月
Realistic heterotic string models require the presence of the Wilson lines. We study the effect of continuous Wilson lines on the heterotic Yukawa couplings for Abelian orbifold compactifications and find that the presence of continuous Wilson lines affects the magnitude of the twisted Yukawa couplings resulting in their stronger hierarchy. (C) 2003 Published by Elsevier B.V., ELSEVIER SCIENCE BV, 英語

Four-dimensional construction of bulk supersymmetry breaking
T Kobayashi, N Maru, K Yoshioka, EUROPEAN PHYSICAL JOURNAL C, 29, 2, 277, 284, 2003年07月
In this letter, we discuss a four-dimensional model with modulus fields which are responsible for supersymmetry breaking. Given a non-trivial moduli dependence of the action, the model is found to give a proper description of higher-dimensional supersymmetry breaking. We explicitly calculate the gaugino and scalar mass spectrum and show that several classes of scenarios proposed in the literature are described in certain regions of the parameter space of the moduli vacuum expectation values. The model in other generic regions of the moduli space gives unexplored scenarios (mass spectra) of supersymmetry breaking in four dimensions., SPRINGER-VERLAG, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Heterotic string backgrounds and CP violation
Tatsuo Kobayashi, Oleg Lebedev, Phys.Lett. B565 (2003) 193-200, 2003年04月25日
In the framework of $Z_N$ orbifolds, we discuss effects of heterotic string

backgrounds including discrete Wilson lines on the Yukawa matrices and their

connection to CP violation., 機関テクニカルレポート，技術報告書，プレプリント等

Finite theories and the supersymmetry flavor problem
KS Babu, T Kobayashi, J Kubo, PHYSICAL REVIEW D, 67, 7, 075018, 2003年04月
We study a finite SU(5) grand unified model based on the non-Abelian discrete symmetry A(4). This model leads to the democratic structure of the mass matrices for the quarks and leptons. In the soft supersymmetry breaking sector, the scalar trilinear couplings are aligned and the soft scalar masses are degenerate, thus solving the SUSY flavor problem., AMER PHYSICAL SOC, 英語, 書評論文,書評,文献紹介等

Yukawa hierarchy transfer based on superconformal dynamics and geometrical realization in string models
T Kobayashi, H Nakano, T Noguchi, H Terao, JOURNAL OF HIGH ENERGY PHYSICS, 0302, 2, 022, 2003年02月
We propose a scenario that leads to hierarchical Yukawa couplings and degenerate sfermion masses at the same time, in the context of extra-dimensional models, which can be naturally embedded in a wide class of string models. The hierarchy of Yukawa couplings and degeneracy of sfermion masses can be realized thanks to superconformal gauge dynamics. The sfermion mass degeneracy is guaranteed by taking the superconformal fixed point to be family independent. In our scenario, the origin of Yukawa hierarchy is attributed to geometry of compactified dimensions and the consequent volume dependence of gauge couplings in the superconformal sectors. The difference in these gauge couplings is dynamically transferred to the hierarchy of the Yukawa couplings. Thus, our scenario combines a new dynamical approach and the conventional geometrical approach of the supersymmetric flavor problem., SPRINGER, 英語

Field localization in warped gauge theories
H Abe, T Kobayashi, N Maru, K Yoshioka, PHYSICAL REVIEW D, 67, 4, 045019, 2003年02月
We present four-dimensional gauge theories that describe physics on five-dimensional curved (warped) backgrounds, which includes bulk fields with various spins (vectors, spinors, and scalars). Field theory on the AdS(5) geometry is examined as a simple example of our formulation. Various properties of bulk fields on this background, e.g., the mass spectrum and field localization behavior, can be achieved within a fully four-dimensional framework. Moreover, that gives a localization mechanism for massless vector fields. We also consider supersymmetric cases, and show in particular that the conditions on bulk masses imposed by supersymmetry on warped backgrounds are derived from a four-dimensional supersymmetric theory on the flat background. As a phenomenological application, models are shown to generate hierarchical Yukawa couplings. Finally, we discuss possible underlying mechanisms which dynamically realize the required couplings to generate curved geometries., AMERICAN PHYSICAL SOC, 英語

Field localization in warped gauge theories
H Abe, T Kobayashi, N Maru, K Yoshioka, PHYSICAL REVIEW D, 67, 4, 2003年02月
We present four-dimensional gauge theories that describe physics on five-dimensional curved (warped) backgrounds, which includes bulk fields with various spins (vectors, spinors, and scalars). Field theory on the AdS(5) geometry is examined as a simple example of our formulation. Various properties of bulk fields on this background, e.g., the mass spectrum and field localization behavior, can be achieved within a fully four-dimensional framework. Moreover, that gives a localization mechanism for massless vector fields. We also consider supersymmetric cases, and show in particular that the conditions on bulk masses imposed by supersymmetry on warped backgrounds are derived from a four-dimensional supersymmetric theory on the flat background. As a phenomenological application, models are shown to generate hierarchical Yukawa couplings. Finally, we discuss possible underlying mechanisms which dynamically realize the required couplings to generate curved geometries., AMERICAN PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

SUSY Flavor Problem and Warped Geometry
Kiwoon Choi, Do Young Kim, Ian-Woo Kim, Tatsuo Kobayashi, 2003年01月18日
We point out that supersymmetric warped geometry can provide a solution to

the SUSY flavor problem, while generating hierarchical Yukawa couplings. In

supersymmetric theories in a slice of AdS_5 with the Kaluza-Klein scale M_KK

much higher than the weak scale, if all visible fields originate from 5D bulk

fields and supersymmetry breaking is mediated by the bulk radion superfield

and/or some brane chiral superfields, potentially dangerous soft scalar masses

and trilinear $A$ parameters at M_KK can be naturally suppressed compared to

the gaugino masses by small warp factor. We present simple models yielding

phenomenologically interesting patterns of soft parameters in this framework., 機関テクニカルレポート，技術報告書，プレプリント等

Wave-function profile and SUSY breaking in 5D model with Fayet-Iliopoulos terms
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Progress of Theoretical Physics, 109, 5, 809, 830, 2003年
We systematically study VEVs of a gauge scalar field Σ in a bulk U(1) vector multiplet and scalar fields in brane/bulk hypermultiplets charged under U(1) in the 5D S1/Z2 orbifold model with generic FI terms. A non-trivial VEV of Σ generates bulk mass terms for U(1) charged fields, and their zero modes have non-trivial profiles. In particular, in the SUSY-breaking case, bosonic and fermionic zero modes have Gaussian profiles. Such non-trivial profiles are useful to explain hierarchical couplings. A toy model for SUSY breaking is studied, and it yields sizable D-term contributions to scalar masses. Because the overall magnitude of D-term contributions is the same everywhere in the bulk and also on both branes, we have to take into account these contributions and other SUSY-breaking terms to obtain a realistic description. We also give profiles and mass eigenvalues of higher modes., Yukawa Institute for Theoretical Physics, 英語

Flavor Violation in Supersymmetric Theories with Gauged Flavor Symmetries
Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao, Koichi Yoshioka, Progress of Theoretical Physics, 110, 2, 247, 267, 2003年
In this paper, we study flavor violation in supersymmetric models with gauged flavor symmetries. There are several sources of flavor violation in these theories. The dominant flavor violation is the tree-level D-term contribution to scalar masses generated by flavor symmetry breaking. We present a new approach for suppressing these phenomenologically dangerous effects by separating the flavor-breaking sector from the supersymmetry-breaking sector. This separation can be achieved either in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor symmetries can yield sizable generation-dependent masses of scalars. Generically the gaugino mass effects are not suppressed, even if the dominant D-term contribution is suppressed. We also analyze the constraints on the flavor symmetry sector resulting from these flavor-violating corrections., Yukawa Institute for Theoretical Physics, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Wave-function profile and SUSY breaking in 5D model with Fayet-Iliopoulos terms
Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Progress of Theoretical Physics, 109, 5, 809, 830, 2003年
We systematically study VEVs of a gauge scalar field Σ in a bulk U(1) vector multiplet and scalar fields in brane/bulk hypermultiplets charged under U(1) in the 5D S1/Z2 orbifold model with generic FI terms. A non-trivial VEV of Σ generates bulk mass terms for U(1) charged fields, and their zero modes have non-trivial profiles. In particular, in the SUSY-breaking case, bosonic and fermionic zero modes have Gaussian profiles. Such non-trivial profiles are useful to explain hierarchical couplings. A toy model for SUSY breaking is studied, and it yields sizable D-term contributions to scalar masses. Because the overall magnitude of D-term contributions is the same everywhere in the bulk and also on both branes, we have to take into account these contributions and other SUSY-breaking terms to obtain a realistic description. We also give profiles and mass eigenvalues of higher modes., Yukawa Institute for Theoretical Physics, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Twisted moduli stabilization in type I string models
Tetsutaro Higaki, Tatsuo Kobayashi, Physical Review D, 68, 4, 2003年
We consider a model with dilaton and twisted moduli fields, which is inspired by type I string models. The stabilization of their vacuum expectation values is studied. We find that the stabilization of the twisted moduli field has different aspects from dilaton stabilization. © 2003 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Sfermion mass degeneracy, superconformal dynamics, and supersymmetric grand unified theories
T Kobayashi, H Nakano, T Noguchi, H Terao, PHYSICAL REVIEW D, 66, 9, 095011, 2002年11月
We discuss issues in a scenario where hierarchical Yukawa couplings are generated through the strong dynamics of superconformal field theories (SCFTs). Independently of the mediation mechanism of supersymmetry breaking, the infrared convergence property of SCFTs can provide an interesting solution to the supersymmetric flavor problem; sfermion masses are suppressed around the decoupling scale of SCFTs and eventually become degenerate to some degree, thanks to family-independent radiative corrections governed by the gaugino masses of the minimal supersymmetric standard model (MSSM). We discuss under what conditions the degeneracy of the sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then explicitly study sfermion mass degeneracy within the framework of grand unified theories coupled to SCFTs. It is found that the degeneracy for right-handed sleptons becomes worse in the conventional SU(5) model than in the MSSM. On the other hand, in the flipped SU(5)xU(1) model, each right-handed lepton is still an SU(5) singlet, whereas the B-ino mass M-1 is determined by two independent gaugino masses of SU(5)xU(1). These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate on how further improvement can be obtained in the SCFT approach., AMER PHYSICAL SOC, 英語

Sfermion mass degeneracy, superconformal dynamics, and supersymmetric grand unified theories
T Kobayashi, H Nakano, T Noguchi, H Terao, PHYSICAL REVIEW D, 66, 9, 2002年11月
We discuss issues in a scenario where hierarchical Yukawa couplings are generated through the strong dynamics of superconformal field theories (SCFTs). Independently of the mediation mechanism of supersymmetry breaking, the infrared convergence property of SCFTs can provide an interesting solution to the supersymmetric flavor problem; sfermion masses are suppressed around the decoupling scale of SCFTs and eventually become degenerate to some degree, thanks to family-independent radiative corrections governed by the gaugino masses of the minimal supersymmetric standard model (MSSM). We discuss under what conditions the degeneracy of the sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then explicitly study sfermion mass degeneracy within the framework of grand unified theories coupled to SCFTs. It is found that the degeneracy for right-handed sleptons becomes worse in the conventional SU(5) model than in the MSSM. On the other hand, in the flipped SU(5)xU(1) model, each right-handed lepton is still an SU(5) singlet, whereas the B-ino mass M-1 is determined by two independent gaugino masses of SU(5)xU(1). These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate on how further improvement can be obtained in the SCFT approach., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa Hierarchy Transfer Based on Superconformal Dynamics and Geometrical Realization in String Models
Tatsuo Kobayashi, Hiroaki Nakano, Tatsuya Noguchi, Haruhiko Terao, JHEP 0302:022,2003, 2002年05月08日
We propose a scenario that leads to hierarchical Yukawa couplings and

degenerate sfermion masses at the same time, in the context of

extra-dimensional models, which can be naturally embedded in a wide class of

string models. The hierarchy of Yukawa couplings and degeneracy of sfermion

masses can be realized thanks to superconformal gauge dynamics. The sfermion

mass degeneracy is guaranteed by taking the superconformal fixed point to be

family independent. In our scenario, the origin of Yukawa hierarchy is

attributed to geometry of compactified dimensions and the consequent volume

dependence of gauge couplings in the superconformal sectors. The difference in

these gauge couplings is dynamically transferred to the hierarchy of the Yukawa

couplings. Thus, our scenario combines a new dynamical approach and the

conventional geometrical approach to the supersymmetric flavor problem., 機関テクニカルレポート，技術報告書，プレプリント等

More about Kaluza-Klein regularization
Tatsuo Kobayashi, Haruhiko Terao, Progress of Theoretical Physics, 107, 4, 785, 792, 2002年04月
We study the so-called "Kaluza-Klein regularization". We calculate one-loop corrections to the Higgs mass due to Kaluza-Klein modes explicitly in a model with SUSY breaking mass splitting between bosonic and fermionic modes. We perform the proper time cutoff at 1/Λ2 and the KK level truncation at ℓ. It is shown that a finite result is obtained as long as ℓ ≫ RΛ for the compactification radius R., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa hierarchy transfer from the superconformal sector and degenerate sfermion masses - art. no. 015004
T Kobayashi, H Nakano, H Terao, PHYSICAL REVIEW D, 65, 1, 015006, 2002年01月
We propose a new type of supersymmetric model coupled to superconformal (SC) field theories, leading simultaneously to hierarchical Yukawa couplings and completely degenerate sfermion masses. We consider models with an extra Abelian gauge symmetry to generate hierarchical structure for couplings between the standard model (SM) sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of model, the flavor-independent structure of the superconformal fixed point guarantees that the sfermion masses of the first and the second generations are completely degenerate at low energy., AMER PHYSICAL SOC, 英語

Yukawa hierarchy transfer from the superconformal sector and degenerate sfermion masses - art. no. 015004
T Kobayashi, H Nakano, H Terao, PHYSICAL REVIEW D, 65, 1, 2002年01月
We propose a new type of supersymmetric model coupled to superconformal (SC) field theories, leading simultaneously to hierarchical Yukawa couplings and completely degenerate sfermion masses. We consider models with an extra Abelian gauge symmetry to generate hierarchical structure for couplings between the standard model (SM) sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of model, the flavor-independent structure of the superconformal fixed point guarantees that the sfermion masses of the first and the second generations are completely degenerate at low energy., AMER PHYSICAL SOC, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenological Implications of Models with Extra Dimensions (第5回新潟・山形合宿)
小林 達夫, 素粒子論研究, 103, 6, F43, F46, 2001年09月20日
素粒子論グループ 素粒子研究編集部, 英語

Direct detection of neutralino dark matter and the anomalons dipole moment of the muon
M Drees, YG Kim, T Kobayashi, MM Nojiri, PHYSICAL REVIEW D, 63, 11, 115009, 2001年06月
We compare predictions for the spin-independent contribution to the neutralino-proton scattering cross section sigma (xp) and for the anomalous magnetic dipole moment of the muon, a(mu)= (g(mu) - 2)/2, in models with gravity-mediated supersymmetry breaking. We nearly always find a positive correlation between these two measurables; i.e., scenarios with larger a(mu) also tend to have larger sigma (xp), but the detailed prediction differs greatly between models. Tn particular, we find that for the popular MSUGRA scenario with universal soft breaking masses at the scale of grand unification, measurements of a(mu) currently seem more promising. On the other hand, if scalar soft breaking masses at the GUT scale receive sizable contributions from SO(10) D terms, one often finds scenarios with large sigma (xp) but a(mu) below the currently foreseen sensitivity. A string-inspired model with a nonuniversal scalar spectrum at the GUT scale falls between these two cases., AMERICAN PHYSICAL SOC, 英語

Fermion mass hierarchies and small mixing angles from extra dimensions
M Bando, T Kobayashi, T Noguchi, K Yoshioka, PHYSICAL REVIEW D, 63, 11, 113017, 2001年06月
In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive the necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimensions. Several specific mechanisms to realize the conditions are presented. We also take into account the generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at a high-energy scale. A toy model is shown to lead to realistic quark mass matrices., AMERICAN PHYSICAL SOC, 英語

Can we distinguish SUSY breaking terms between weakly and strongly coupled heterotic string theories?
Tatsuo Kobayashi, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 506, 1-2, 187, 192, 2001年05月03日
We study soft SUSY breaking terms in heterotic M-theory. We show that both weakly and strongly coupled heterotic string models lead to the same relations of soft SUSY breaking terms, A = -M and m2 = M2/3, up to O((αT/S)2). © 2001 Published by Elsevier Science B.V., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Restricted flavor structure of soft SUSY breaking trilinear couplings
T Kobayashi, O Vives, PHYSICS LETTERS B, 506, 3-4, 323, 330, 2001年05月
We analyze the flavor structure of the trilinear couplings in the different theoretical models of SUSY breaking. We generically obtain A(ij) = A(i)(L) + A(j)(R) in all the models examined. In fact, this is the rigorous form when SUSY breaking effects appear through the Kahler metric of chiral fields or through wave-function renormalization. Indeed, the low-energy phenomenological requirements from the absence of charge and color breaking minima and the measurements in flavor changing neutral current (FCNC) observables strongly favor this restricted form of the trilinear matrices. As a straightforward consequence the number of unknown parameters associated with the trilinear couplings is decreased in a factor of 2. (C) 2001 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

29pSJ-3 SUSY breaking mediation in extra dimensions
小林 達夫, 日本物理学会講演概要集, 56, 1, 7, 7, 2001年03月09日
一般社団法人日本物理学会, 日本語

Sfermion masses in Nelson-Strassler-Type models : SUSY standard models coupled with SCFTs(??)　　　　　　　　　　　　　　　
Phys. Rev., D64, 075003, 2001年

Direct detection of neutralino dark matter and the anomalous dipole moment of the muon
Manuel Drees, Yeong Gyun Kirn, Tatsuo Kobayashi, Mihoko M. Nojiri, Physical Review D, 63, 11, 2001年
We compare predictions for the spin-independent contribution to the neutralino-proton scattering cross section σχp and for the anomalous magnetic djpole moment of the muon, aμ=(gμ- 2)12, in models with gravity-mediated supersymmetry breaking. We nearly always find a positive correlation between these two measurables
i.e.,' 'scenarios with larger aμ also tend to have larger σχp, but the detailed prediction differs greatly between models. In particular, we find that for the popular MSUGRA scenario with universal soft breaking masses at the scale of grand unification, measurements of aμ currently seem more promising. On the other hand, if scalar soft breaking masses at the GUT scale receive sizable contributions from SO(10) D terms, one often finds scenarios with large σχp but aμ below the currently foreseen sensitivity. A string-inspired model with a nonuniversal scalar spectrum at the GUT scale falls between these two cases. ©2001 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Fermion mass hierarchies and small mixing angles from extra dimensions
Masako Bando, Tatsuo Kobayashi, Tatsuya Noguchi, Koichi Yoshioka, Physical Review D, 63, 11, 2001年
In this paper we study renormalization-group evolutions of Yukawa matrices enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point structure. We derive the necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimensions. Several specific mechanisms to realize the conditions are presented. We also take into account the generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at a high-energy scale. A toy model is shown to lead to realistic quark mass matrices. © 2001 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Sfermion masses in Nelson-Strassler-type models: Supersymmetric standard models coupled with superconformal field theories
Tatsuo Kobayashi, Haruhiko Terao, Physical Review D, 64, 7, 2001年
We study soft supersymmetric (SUSY) breaking parameters in the Nelson-Strassler-type models: SUSY standard models coupled with superconformal field theories (SCFT's). In this type of model, soft SUSY breaking parameters including sfermion masses can be suppressed around the decoupling scale of SCFT's. We clarify the condition to derive exponential suppression of sfermion masses within the framework of pure SCFT's. Such behavior is favorable for degeneracy of sfermion masses. However, the realistic sfermion masses are not quite degenerate due to the gauge couplings and the gaugino masses in the standard model sector. We show the sfermion mass spectrum obtained in such models. The aspect of suppression for the soft SUSY breaking parameters is also demonstrated in an explicit model. We also give a mechanism generating the μ term of the electroweak scale by a singlet field coupled with the SCFT. ©2001 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Kaluza-Klein mediated supersymmetry breaking
T Kobayashi, K Yoshioka, PHYSICAL REVIEW LETTERS, 85, 26, 5527, 5530, 2000年12月
The four-dimensional effective theories with compactified extra dimensions are considered. We then discuss a new framework for communicating supersymmetry breaking to the visible sector where the radius modulus, which determines the size of extra dimensions, has an auxiliary vacuum expectation value. The modulus couplings generate mass splitting in Kaluza-Klein supermultiplets and they act as messengers of supersymmetry breaking. The soft mas ses are expressed in terms of renormalization-group functions and the sparticle spectrum is determined by what kind of field propagates in the bulk., AMER PHYSICAL SOC, 英語

Softly broken supersymmetric Gauge-Higgs-Yukawa theories as renormalizable composite models
Tatsuo Kobayashi, Haruhiko Terao, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 489, 1-2, 233, 242, 2000年09月14日
We examine the (softly broken) supersymmetric gauge-Higgs-Yukawa theories satisfying the compositeness conditions at a certain scale. In these theories the Higgs superfields can be regarded as the chiral composite fields. It is found that there are the fundamental theories, which contain the dimension 5 interactions and the hard SUSY breaking in perturbation, turn to be renormalizable and also softly broken theories in the nonperturbative framework. The soft SUSY breaking parameters as well as the Yukawa coupling in the corresponding gauge-Higgs-Yukawa theories are restricted by the renormalization group invariant relations. (C) 2000 Published by Elsevier Science B.V., 英語

Kaluza-Klein Mediated Supersymmetry Breaking
Tatsuo Kobayashi, Koichi Yoshioka, Phys.Rev.Lett. 85 (2000) 5527-5530, 2000年08月08日
We discuss a framework for communicating supersymmetry breaking to the

visible sector where the radius modulus, which determines the size of extra

dimensions, has an auxiliary vacuum expectation value. The modulus couplings

generate mass splitting in Kaluza-Klein supermultiplets and they act as

messengers of supersymmetry breaking. The soft masses are expressed in terms of

renormalization-group functions and the sparticle spectrum is determined by

what kind of field propagates in the bulk. This framework also provides new

possibilities for solving the supersymmetric flavor problem., 機関テクニカルレポート，技術報告書，プレプリント等

New RG-invariants of soft supersymmetry breaking parameters
Tatsuo Kobayashi, Koichi Yoshioka, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 486, 1-2, 223, 227, 2000年07月27日
We study new renormalization-group invariant quantities of soft supersymmetry breaking parameters other than the ratio of gaugino mass to gauge coupling squared by using the spurion method. The obtained invariants are useful to probe supersymmetry breaking and μ-term generation mechanisms at high-energy scale. We also discuss the convergence behavior of fixed points of supersymmetry breaking parameters. (C) 2000 Elsevier Science B.V., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

EDM-free supersymmetric CP violation with non-universal soft terms
S Khalil, T Kobayashi, O Vives, NUCLEAR PHYSICS B, 580, 1-2, 275, 288, 2000年07月
Non-universality in the soft breaking terms is a common feature in most superstring inspired SUSY models. This property is required to obtain sizeable CP violation effects from SUSY and, on the other hand, can be used to avoid the electric dipole moment (EDM) constraints. We take advantage of these qualities and explore a class of SUSY models based on type I string theory where scalar masses, gaugino masses and trilinear couplings are non-universal. In this framework, we show that, in the presence of large SUSY phases, the bounds on the electric dipole moments can be controlled without fine-tuning. At the same time, we find that these phases, free from EDM constraints, lead to large contributions to the observed CP phenomena in Kaon system and, in particular, to direct CP violation in epsilon'/epsilon. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Electroweak symmetry breaking and s-spectrum in M-theory
T Kobayashi, J Kubo, H Shimabukuro, NUCLEAR PHYSICS B, 580, 1-2, 3, 28, 2000年07月
We study soft SUSY breaking parameters in M-theory with and without 5-brane moduli fields. We investigate successful electroweak symmetry breaking and the positivity of stau mass squared. A value of alpha(T + (T) over bar) is phenomenologically constrained. Also we have phenomenological constraints on magnitudes of derivatives of the Kahler potential for the 5-brane moduli field. We study mass spectra in the allowed regions. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Softly Broken Supersymmetric Gauge-Higgs-Yukawa Theories as Renormalizable Composite Models
Tatsuo Kobayashi, Haruhiko Terao, Phys.Lett. B489 (2000) 233-242, 2000年05月26日
We examine the (softly broken) supersymmetric gauge-Higgs-Yukawa theories

satisfying the compositeness conditions at a certain scale. In these theories

the Higgs superfields can be regarded as the chiral composite fields. It is

found that there are the fundamental theories, which contain the dimension 5

interactions and the hard SUSY breaking in perturbation, turn to be

renormalizable and also softly broken theories in the nonperturbative

framework. The soft SUSY breaking parameters as well as the Yukawa coupling in

the corresponding gauge-Higgs-Yukawa theories are restricted by the

renormalization group invariant relations., 機関テクニカルレポート，技術報告書，プレプリント等

RG-invariant Sum Rule in Anomaly Mediated SUSY Breaking
小林 達夫, 素粒子論研究, 101, 2, B25, B26, 2000年05月20日
素粒子論グループ 素粒子研究編集部, 英語

Yukawa hierarchy from extra dimensions and infrared fixed points
Masako Bando, Tatsuo Kobayashi, Tatsuya Noguchi, Koichi Yoshioka, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 480, 1-2, 187, 192, 2000年05月04日
We discuss the existence of hierarchy of Yukawa couplings in the models with extra spatial dimensions. The hierarchical structure is induced by the power behavior of the cutoff dependence of the evolution equations which yield large suppressions of couplings at the compactification scale. The values of coupling constants at this scale can be made stable almost independently of the initial input parameters by utilizing the infrared fixed point. We find that the Yukawa couplings converge to the fixed points very quickly because of the enhanced energy dependence of the suppression factor from extra dimensions as well as in the Case of large gauge couplings at high-energy scale. (C) 2000 Published by Elsevier Science B.V., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa hierarchy from extra dimensions and infrared fixed points
M Bando, T Kobayashi, T Noguchi, K Yoshioka, PHYSICS LETTERS B, 480, 1-2, 187, 192, 2000年05月
We discuss the existence of hierarchy of Yukawa couplings in the models with extra spatial dimensions. The hierarchical structure is induced by the power behavior of the cutoff dependence of the evolution equations which yield large suppressions of couplings at the compactification scale. The values of coupling constants at this scale can be made stable almost independently of the initial input parameters by utilizing the infrared fixed point. We find that the Yukawa couplings converge to the fixed points very quickly because of the enhanced energy dependence of the suppression factor from extra dimensions as well as in the case of large gauge couplings at high-energy scale. (C) 2000 Published by Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

RG-invariant Sum Rule in a Generalization of Anomaly Mediated SUSY Breaking Models
Marcela Carena, Katri Huitu, Tatsuo Kobayashi, Nucl.Phys.B592:164-182,2001, 2000年03月20日
We study a generalization of anomaly-mediated supersymmetry breaking (AMSB)

scenarios, under the assumption that the effects of the high-scale theory do

not completely decouple and D-term type contributions can be therefore present.

We investigate the effect of such possible D-term additional contributions to

soft scalar masses by requiring that, for non-vanishing, renormalizable Yukawa

couplings $Y^{ijk} $, the sum of squared soft supersymmetry breaking mass

parameters, $M^2_{ijk} \equiv m_i^2+m_j^2+m_k^2$, is RG-invariant, in the sense

that it becomes independent of the specific ultraviolet boundary conditions as

it occurs in the AMSB models. These type of models can avoid the problem of

tachyonic solutions for the slepton mass spectrum present in AMSB scenarios. We

implement the electroweak symmetry breaking condition and explore the sparticle

spectrum associated with this framework. To show the possible diversity of the

sparticle spectrum, we consider two examples, one in which the D-terms induce a

common soft supersymmetry breaking mass term for all sfermion masses, and

another one in which a light stop can be present in the spectrum., 機関テクニカルレポート，技術報告書，プレプリント等

EDM-free supersymmetric CP violation with non-universal soft terms
Shaaban Khalil, Tatsuo Kobayashi, Oscar Vives, Nucl.Phys. B580 (2000) 275-288, 2000年03月10日
Non-universality in the soft breaking terms is a common feature in most

superstring inspired SUSY models. This property is required to obtain sizeable

CP violation effects from SUSY and, on the other hand, can be used to avoid the

Electric Dipole Moment constraints. We take advantage of these qualities and

explore a class of SUSY models based on type I string theory where scalar

masses, gaugino masses and trilinear couplings are non-universal. In this

framework, we show that, in the presence of large SUSY phases, the bounds on

the Electric Dipole Moments can be controled without fine-tuning. At the same

time, we find that these phases, free from EDM constraints, lead to large

contributions to the observed CP phenomena in Kaon system and, in particular,

to direct CP violation in epsilon'/epsilon., 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenological constraints on SUSYSU(5) GUTs with nonuniversal gaugino masses
K Huitu, Y Kawamura, T Kobayashi, K Puolamaki, PHYSICAL REVIEW D, 61, 3, 035001, 2000年02月
We study the phenomenological aspects of supersymmetric SU(5) grand unified theories with nonuniversal gaugino masses. For large tan beta, we investigate constraints fi-om the requirement of successful electroweak symmetry breaking, the positivity of stau mass squared, and the b-->s gamma decay rate. In the allowed region, the nature of the lightest supersymmetric particle is determined. Examples of mass spectra are given. We also calculate loop corrections to the bottom mass due to superpartners., AMER PHYSICAL SOC, 英語

"RG-invariant Sum Rule in a Generalization of Anomaly-Mediated SUSY Breaking Models"(jointly worked)　　　　　　　　　　　　　　　
Nucl. Phys., B592, 164, 182, 2000年

"Infrared alignment of SUSY flavor structures"(jointly worked)　　　　　　　　　　　　　　　
Phys. Rev., D62, 115003, 2000年

Bottom-up approach to B-parameter in minimal supersymmetric standard model
Y Kawamura, T Kobayashi, M Watanabe, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 15, 1, 81, 103, 2000年01月
We study mu and B-parameters in the minimal supersymmetric standard model (MSSM) based on the radiative electroweak symmetry breaking scenario using "bottom-up" approach and show how useful our approach is to select a phenomenologically viable model beyond the MSSM under the assumption that the underlying theory is a string model or a gauge-Yukawa unified gauge model., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

Phenomenological constraints on SUSYSU(5) GUTs with non-universal gaugino masses
K Huitu, Y Kawamura, T Kobayashi, K Puolamaki, HIGH ENERGY PHYSICS 99, PROCEEDINGS, 786, 788, 2000年
We study phenomenological aspects of supersymmetric SU(5) grand unified theories with non-universal gaugino masses. For large tan beta, we investigate constraints from the requirement of successful electroweak symmetry breaking, the positivity of stau mass squared and the b --> s gamma decay rate. We also calculate loop corrections to the bottom mass due to superpartners., IOP PUBLISHING LTD, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Infrared alignment of supersymmetric flavor structures
Tatsuo Kobayashi, Physical Review D - Particles, Fields, Gravitation and Cosmology, 62, 11, 8, 2000年
The various experimental bounds on flavor-changing interactions severely restrict the low-energy flavor structures of soft supersymmetry breaking parameters. In this work, we show that with a particular assumption of Yukawa couplings, the fermion mass and sfermion soft mass matrices are simultaneously diagonalized by common mixing matrices and we then obtain an alignment solution for the flavor problems. The required condition is generated by renormalization group evolutions and achieved at low-energy scale independently of high-energy structures of couplings. In this case, the diagonal entries of the soft scalar mass matrices are determined by gaugino and Higgs boson soft masses. We also discuss possible realizations of this scenario and the characteristic sparticle spectrum in the models. © 2000 The American Physical Society., 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Generic gravitational corrections to gauge couplings in SUSYSU(5) GUTs
K Huitu, Y Kawamura, T Kobayashi, K Puolamaki, PHYSICS LETTERS B, 468, 1-2, 111, 117, 1999年11月
We study non-universal corrections to the gauge couplings due to higher dimensional operators in supersymmetric SU(5) grand unified theories. The corrections are, in general, parametrized by three components originating from 24, 75 and 200 representations. We consider the prediction of alpha(3)(M-z) along each 24, 75 and 200 direction, and their linear combinations. The magnitude of GUT scale and its effects on proton decay are discussed. Non-SUSY case is also examined. (C) 1999 Published by Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

F-term inflation in M-theory with five-branes
SM Harun-or-Rashid, T Kobayashi, H Shimabukuro, PHYSICS LETTERS B, 466, 2-4, 95, 99, 1999年11月
We study F-term inflation in M-theory with and without five-brane moduli fields. We show the slow rolling condition is not satisfied in M-theory without five-brane moduli fields, but it can be satisfied in the case with non-vanishing F-terms of five-brane moduli fields. (C) 1999 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

CP violation in a supersymmetric model with nondegenerate A terms
S Khalil, T Kobayashi, A Masiero, PHYSICAL REVIEW D, 60, 7, 075003, 1999年10月
We study the CP phases of the soft supersymmetry breaking terms in string-inspired models with nonuniversal trilinear couplings. We show that such nonuniversality plays an important role on all CP violating processes. In particular these new supersymmetric sources of CP violation may significantly contribute to the observed CP phenomena in kaon physics while respecting the severe bound on the electric dipole moment of the neutron. [S0556-2821(99)03217-8]., AMERICAN PHYSICAL SOC, 英語

Generic Gravitational Corrections to Gauge Couplings in SUSY SU(5) GUTs
Katri Huitu, Yoshiharu Kawamura, Tatsuo Kobayashi, Kai Puolamaki, Phys.Lett. B468 (1999) 111-117, 1999年09月02日
We study non-universal corrections to the gauge couplings due to higher

dimensional operators in supersymmetric SU(5) grand unified theories. The

corrections are, in general, parametrized by three components originating from

{\bf 24}, {\bf 75} and {\bf 200} representations. We consider the prediction of

$\alpha_3(M_Z)$ along each {\bf 24}, {\bf 75} and {\bf 200} direction, and

their linear combinations. The magnitude of GUT scale and its effects on proton

decay are discussed. Non-SUSY case is also examined., 機関テクニカルレポート，技術報告書，プレプリント等

Gauge Coupling Unification with Extra Dimensions and Correction due to Higher Dimensional Operators
Katri Huitu, Tatsuo Kobayashi, Phys.Lett. B470 (1999) 90-94, 470, 1/4, 90, 94, 1999年06月21日
We study the gauge coupling unification with extra dimensions. We take into

account corrections due to the higher dimensional operators. We show the

prediction of $\alpha_3(M_Z)$ is sensitive to such corrections, even if

$c<\Phi>/M=O(0.01)$. We also discuss the $b-\tau$ Yukawa unification., 機関テクニカルレポート，技術報告書，プレプリント等

Supersymmetric CP violation $ε'/ε$ due to asymmetric A-matrix
Shaaban Khalil, Tatsuo Kobayashi, Phys.Lett.B460:341-347,1999, B460, 341, 347, 1999年06月16日
We study contributions of supersymmetric CP phases to the CP violation

$\epsilon'/\epsilon$ in models with asymmetric $A$-matrices. We consider

asymmetric $A$-matrices, which are obtained from string-inspired supergravity.

We show that a certain type of asymmetry of $A$-matrices enhances

supersymmetric contributions to the CP violation $\epsilon'/\epsilon$ and the

supersymmetric contribution to $\epsilon'/\epsilon$ can be of order of the KTeV

result, $\epsilon'/\epsilon \sim 10^{-3}$., 機関テクニカルレポート，技術報告書，プレプリント等

Running of soft parameters in extra space-time dimensions
Tatsuo Kobayashi, Jisuke Kubo, Myriam Mondragón, George Zoupanos, Nuclear Physics B, 550, 1-2, 99, 122, 1999年06月14日
The evolution of the parameters including those in the soft supersymmetry-breaking (SSB) sector is studied in the minimal supersymmetric standard model (MSSM) with a certain set of Kaluza-Klein towers which has been recently considered by Dienes et al. We use the continuous Wilson renormalization group technique to derive the one-loop matching condition between the effective, renormalizable and original, unrenormalizable theories. We investigate whether the assumption of a large compactification radius in the model is consistent with the gauge coupling unification, the b-τ unification and the radiative breaking of the electroweak gauge symmetry with the universal SSB terms. We calculate the superpartner spectrum under the assumption of the universal SSB parameters to find differences between the model and the MSSM. © 1999 Elsevier Science B.V. All rights reserved., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Running of soft parameters in extra space-time dimensions
T Kobayashi, J Kubo, M Mondragon, G Zoupanos, NUCLEAR PHYSICS B, 550, 1-2, 99, 122, 1999年06月
The evolution of the parameters including those in the soft supersymmetry-breaking (SSB) sector is studied in the minimal supersymmetric standard model (MSSM) with a certain set of Kaluza-Klein towers which has been recently considered by Dienes et al. We use the continuous Wilson renormalization group technique to derive the one-loop matching condition between the effective, renormalizable and original, unrenormalizable theories. We investigate whether the assumption of a large compactification radius in the model is consistent with the gauge coupling unification, the b-tau unification and the radiative breaking of the electroweak gauge symmetry with the universal SSB terms. We calculate the superpartner spectrum under the assumption of the universal SSB parameters to find differences between the model and the MSSM. (C) 1999 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Electroweak symmetry breaking and s-spectrum in M-theory
Tatsuo Kobayashi, Jisuke Kubo, Hitoshi Shimabukuro, Nucl.Phys. B580 (2000) 3-28, 1999年04月01日
We study soft SUSY breaking parameters in M-theory with and without 5-brane

moduli fields. We investigate successful electroweak symmetry breaking and the

positivity of stau mass squared. We study mass spectra in allowed regions., 機関テクニカルレポート，技術報告書，プレプリント等

CP violation in supersymmetric model with non-degenerate A-terms
Shaaban Khalil, Tatsuo Kobayashi, Antonio Masiero, Phys.Rev. D60 (1999) 075003, 1999年04月01日
We study the CP phases of the soft supersymmetry breaking terms in

string-inspired models with non-universal trilinear couplings. We show that

such non-universality plays an important role on all CP violating processes. In

particular these new supersymmetric sources of CP violation may significantly

contribute to the observed CP phenomena in kaon physics while respecting the

severe bound on the electric dipole moment of the neutron., 機関テクニカルレポート，技術報告書，プレプリント等

On Different Criteria for Confinement
Masud Chaichian, Tatsuo Kobayashi, Phys.Lett. B481 (2000) 26-32, 481, 1, 26, 32, 1999年03月12日
We compare two approaches in supersymmetric confinement, the Seiberg

formulation and the superconvergence rule. For the latter, the critical point

is $\gamma_{00}=0$ in the Landau gauge. We find $4\gamma_{00}=\beta_0$ is the

critical point for most of confining theories without a tree-level

superpotential in the Seiberg formulation, in particular, in the large $N_c$

and $N_f$ limit. We show how confining theories with a discrete symmetry and a

tree-level superpotential connect these two critical points: the large and

small discrete symmetry limits correspond to the critical points

$4\gamma_{00}=\beta_0$ and $\gamma_{00}=0$, respectively., 機関テクニカルレポート，技術報告書，プレプリント等

F-term inflation in M-theory with five-branes
S. M. Harun-or-Rashid, Tatsuo Kobayashi, Hitoshi Shimabukuro, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 466, 2-4, 95, 99, 1999年
We study F-term inflation in M-theory with and without five-brane moduli fields. We show the slow rolling condition is not satisfied in M-theory without five-brane moduli fields, but it can be satisfied in the case with non-vanishing F-terms of five-brane moduli fields. © 1999 Elsevier Science B.V. All rights reserved., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Constraints on finite soft supersymmetry breaking terms
T Kobayashi, J Kubo, M Mondragon, G Zoupanos, INTERNATIONAL EUROPHYSICS CONFERENCE ON HIGH ENERGY PHYSICS, 877, 882, 1999年
A new solution to the requirement of two-loop finiteness of the soft supersymmetry breaking terms (SSB) parameters is found in Finite-Gauge-Yukawa unified theories. The new solution has the form of a sum rule for the relevant scaler masses, relaxing the universality required by the previously known solution, which leads to models with unpleasant phenomenological consequences. Using the sum rule we investigate two Finite-Gange-Yukawa unified models and we determine their spectrum in terms of few parameters. Some characteristic features of the models are that a) the old agreement of the top quark mass prediction with the measured value remains unchanged, b) the lightest Higgs mass is predicted around 120 GeV, c) the s-spectrum starts above 200 GeV., SPRINGER-VERLAG BERLIN, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

M理論の低エネルギー有効理論におけるふく射補正による電弱対称性の破れ
久保治輔, 小林達夫, 島袋均, 日本物理学会北陸支部・応用物理学会北陸・信越支部合同講演会講演予稿集, 1998, 17, 1998年12月
日本語

Infrared behaviour of softly broken SQCD and its dual
A Karch, T Kobayashi, J Kubo, G Zoupanos, PHYSICS LETTERS B, 441, 1-4, 235, 242, 1998年11月
Applying the recently obtained results on the renormalization of soft supersymmetry-breaking parameters, we investigate the infrared behaviour of the softly broken supersymmetric QCD as well as its dual theory in the conformal window. Under general assumptions on beta-functions, it is shown that the soft supersymmetry-breaking parameters asymptotically vanish in the infrared limit so that superconformal symmetry in softly broken supersymmetric QCD and in its dual theory revives at the infrared fixed point, provided the soft scalar masses satisfy certain renormalization group invariant relations. If these relations are not satisfied, there exist marginal operators in both theories that lead to the breaking of supersymmetry and also colour symmetry. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Constraints on supersymmetric SO(10) GUTs with sum rules among soft masses
Y Kawamura, T Kobayashi, H Shimabukuro, PHYSICS LETTERS B, 436, 1-2, 108, 116, 1998年09月
We study phenomenological aspects of supersymmetric SO(10) GUTs with sum rules among soft SUSY breaking parameters, In particular, the sum rule related to the stau mass leads to the constraints from the requirements of successful electroweak breaking and the positivity of stau mass squared. The bottom quark mass is also estimated. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Infrared Behaviour of Softly Broken SQCD and Its Dual
Andreas Karch, Tatsuo Kobayashi, Jisuke Kubo, George Zoupanos, Phys.Lett. B441 (1998) 235-242, 1998年08月29日
Applying the recently obtained results on the renormalization of soft

supersymmetry-breaking parameters, we investigate the infrared behaviour of the

softly broken supersymmetric QCD as well as its dual theory in the conformal

window. Under general assumptions on $\beta$-functions, it is shown that the

soft supersymmetry-breaking parameters asymptotically vanish in the infrared

limit so that superconformal symmetry in softly broken supersymmetric QCD and

in its dual theory revives at the infrared fixed point, provided the soft

scalar masses satisfy certain renormalization group invariant relations. If

these relations are not satisfied, there exist marginal operators in both

theories that lead to the breaking of supersymmetry and also colour symmetry., 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa unification in moduli-dominant SUSY breaking
Shaaban Khalil, Tatsuo Kobayashi, Nuclear Physics B, 526, 1-3, 99, 114, 1998年08月24日
We study Yukawa unification in string models with moduli-dominant SUSY breaking. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Such non-universality is important for phenomenological aspects of Yukawa unification, i.e., successful electroweak breaking, SUSY corrections to the bottom mass and the branching ratio of b → sγ, We show three regions in the whole parameter space that lead to successful electroweak breaking and allow small SUSY corrections to the bottom mass. For these three regions we investigate the b → sγ decay and mass spectra. © 1998 Elsevier Science B.V., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Vacuum Structure of Softly Broken N=1 Supersymmetric QCD
Masud Chaichian, Tatsuo Kobayashi, Phys.Lett. B442 (1998) 192-198, 1998年08月19日
We study softly broken N=1 supersymmetric QCD with the gauge group $SU(N_c)$

and $N_f$ flavors of quark pairs. We investigate vacuum structure of the theory

with generic soft supersymmetry breaking terms. Trilinear soft breaking terms

play an essential role in determining vacua. For $N_f=N_c+1$, chiral symmetry

is broken for a sufficiently large magnitude of trilinear couplings, while it

is unbroken in the case with only soft masses. In the case where appearance of

trilinear coupling terms is allowed, i.e. for $N_f \geq N_c+1$, we have two

possible vacua, the trivial and non-trivial ones. Otherwise, we only have the

non-trivial vacuum, which corresponds to the non-trivial vacuum in the $N_f

\geq N_c+1$ theory., 機関テクニカルレポート，技術報告書，プレプリント等

Yukawa unification in moduli-dominant SUSY breaking
S Khalil, T Kobayashi, NUCLEAR PHYSICS B, 526, 1-3, 99, 114, 1998年08月
We study Yukawa unification in string models with moduli-dominant SUSY breaking. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Such non-universality is important for phenomenological aspects of Yukawa unification, i.e., successful electroweak breaking, SUSY corrections to the bottom mass and the branching ratio of b --> s gamma, We show three regions in the whole parameter space that lead to successful electroweak breaking and allow small SUSY corrections to the bottom mass. For these three regions we investigate the b --> s gamma decay and mass spectra, (C) 1998 Elsevier Science B.V., ELSEVIER SCIENCE BV, 英語

Quark Mass Matrices in String Models (フレ-バ-の物理とその周辺)
小林 達夫, 素粒子論研究, 97, 4, D31, D33, 1998年07月20日
素粒子論グループ 素粒子研究編集部, 英語

Softly broken N = 1 supersymmetric QCD
M Chaichian, WF Chen, T Kobayashi, PHYSICS LETTERS B, 432, 1-2, 120, 127, 1998年07月
We study softly broken N=1 supersymmetric QCD with the gauge group SU(N-c) and Nf flavours of quarks for N-f > N-c + 1. We investigate the phase structure of its dual theory adding generic soft supersymmetry breking terms, i.e. soft scalar masses, trilinear coupling terms of scalar fields and gaugino masses. It is found that the trilinear coupling terms play an important role in determining the potential minima. Also we compare softly broken original and dual theories in the broken phase. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Sum rules in the superpartner spectrum of the minimal supersymmetric standard model
Y Kawamura, T Kobayashi, J Kubo, PHYSICS LETTERS B, 432, 1-2, 108, 113, 1998年07月
Assuming that the universal sum rules for soft supersymmetry-breaking terms, which have been recently found both in four-dimensional superstring models and in supersymmertic gauge-Yukawa unified gauge models, are satisfied above and at the grand unification scale, we investigate their low energy consequences and derive sum rules in the superpartner spectrum of the minimal supersymmetric standard model (MSSM). These sum rules contain only observable parameters of the MSSM, and could be experimentally verified in future. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Constraints on Supersymmetric SO(10) GUTs with Sum Rules among Soft Masses
Yoshiharu Kawamura, Tatsuo Kobayashi, Hitoshi Shimabukuro, Phys.Lett.B436:108-116,1998, 1998年05月15日
We study phenomenological aspects of supersymmetric SO(10) GUTs with sum

rules among soft SUSY breaking parameters. In particular, the sum rule related

to the stau mass leads to the constraints from the requirements of successful

electroweak breaking and the positivity of stau mass squared. The bottom quark

mass is also estimated., 機関テクニカルレポート，技術報告書，プレプリント等

Further all-loop results in softly-broken supersymmetric gauge theories
T Kobayashi, J Kubo, G Zoupanos, PHYSICS LETTERS B, 427, 3-4, 291, 299, 1998年05月
It is proven that the recently found, renormalization-group invariant sum rule for the soft scalar masses in softly-broken N=l supersymmetric gauge-Yukawa unified theories can be extended to all orders in perturbation theory. Ln the case of finite unified theories, the sum rule ensures the all-loop finiteness in the soft supersymmetry breaking sector. As a byproduct the exact beta function for the soft scalar masses in the Novikov-Shifman-Vainstein-Zakharov (NSVZ) scheme for softly-broken supersymmetric QCD is obtained. It is also found that the singularity appearing in the sum rule in the NSVZ scheme exactly coincides with that which has been previously found in a certain class of superstring models in which the massive string states are organized into N=4 supermultiplets. (C) 1998 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, 英語

Softly Broken N=1 Supersymmetric QCD
Masud Chaichian, Wen-Feng Chen, Tatsuo Kobayashi, Phys.Lett. B432 (1998) 120-127, 1998年03月18日
We study softly broken N=1 supersymmetric QCD with the gauge group $SU(N_c)$

and $N_f$ flavours of quarks for $N_f > N_c+1$. We investigate the phase

structure of its dual theory adding generic soft supersymmetry breking terms,

i.e. soft scalar masses, trilinear coupling terms of scalar fields and gaugino

masses. It is found that the trilinear coupling terms play an improtant role in

determining the potential minima. Also we compare softly broken original and

dual theories in the broken phase., 機関テクニカルレポート，技術報告書，プレプリント等

Bottom-up approach to B-parameter in minimal supersymmetric standard model
Yoshiharu Kawamura, Tatsuo Kobayashi, Manabu Watanabe, Int.J.Mod.Phys. A15 (2000) 81-104, 1998年02月16日
We study $\mu$ and $B$-parameters in the minimal supersymmetric standard

model (MSSM) based on the radiative electroweak symmetry breaking scenario

using $\lq\lq$bottom-up" approach and show how useful our approach is to select

a phenomenologically viable model beyond the MSSM under the assumption that the

underlying theory is a string model or a gauge-Yukawa unified gauge model., 機関テクニカルレポート，技術報告書，プレプリント等

Probing μ-term generation mechanism in string models
Yoshiharu Kawamura, Tatsuo Kobayashi, Manabu Watanabe, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 419, 1-4, 157, 166, 1998年02月11日
We give a generic method to select a realistic μ-term generation mechanism based on the radiative electroweak symmetry breaking scenario and study which type is hopeful within the framework of string theory. We discuss effects of the moduli F-term condensation and D-term contribution to soft scalar masses. © 1998 Elsevier Science B.V., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Further all-loop results in softly-broken supersymmetric gauge theories
Tatsuo Kobayashi, Jisuke Kubo, George Zoupanos, Phys.Lett.B427:291-299,1998, 1998年02月07日
It is proven that the recently found, renormalization-group invariant sum

rule for the soft scalar masses in softly-broken N=1 supersymmetric

gauge-Yukawa unified theories can be extended to all orders in perturbation

theory. In the case of finite unified theories, the sum rule ensures the

all-loop finiteness in the soft supersymmetry breaking sector. As a byproduct

the exact $\beta$ function for the soft scalar masses in the

Novikov-Shifman-Vainstein-Zakharov (NSVZ) scheme for softly-broken

supersymmetric QCD is obtained. It is also found that the singularity appearing

in the sum rule in the NSVZ scheme exactly coincides with that which has been

previously found in a certain class of superstring models in which the massive

string states are organized into $N = 4$ supermultiplets., 機関テクニカルレポート，技術報告書，プレプリント等

Constraints on finite soft supersymmetry-breaking terms
T Kobayashi, J Kubo, M Mondragon, G Zoupanos, NUCLEAR PHYSICS B, 511, 1-2, 45, 68, 1998年02月
Requiring the soft supersymmetry-breaking (SSB) parameters in finite gauge-Yukawa unified models to be finite up to and including two-loop order, we derive a two-loop sum rule for the soft scalar masses, It is shown that this sum rule coincides with that of a certain class of string models in which the massive string states are organized into N = 4 supermultiplets. We investigate the SSB sector of two finite SU(5) models. Using the sum rule which allows non-universality of the SSB terms and requiring that the lightest superparticle is neutral, we constrain the parameter space of the SSB sector in each model. (C) 1998 Elsevier Science B.V., ELSEVIER SCIENCE BV, 英語, 書評論文,書評,文献紹介等

"Vacuum Structure of Softly Broken N=1 Supersymmetric QCD"(jointly worked)
Phys. Lett., 442, 1/4, 192, 198, 1998年

"Quark Mass Matrices in Superstring Models"(jointly worked)
Int. J. Mod. Phys., 13, 13, 2201, 2215, 1998年

Notes on Curtright-Zachos deformations of osp(1,2) and super Virasoro algebras
N Aizawa, T Kobayashi, HT Sato, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 12, 32, 5867, 5883, 1997年12月
Based on the quantum superspace construction of q-deformed algebra, we discuss a supersymmetric extension of the deformed Virasoro algebra, which is a subset of the q-W-infinity algebra which recently appeared in the context of two-dimensional string theory. We analyze two types of deformed super Virasoro algebra as well as their osp(1,2) subalgebras. Applying our quantum superspace structure to conformal field theory, we find the same type of deformation of affine sl(2) algebra., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

SO(10)型SUSYGUT modelにおける,soft mass parameterのsum ruleとその許される領域
久保治輔, 小林達夫, 島袋均, 日本物理学会北陸支部・応用物理学会北陸・信越支部合同講演会講演予稿集, 1997, 146, 1997年12月
日本語

Sum rules in the superpartner spectrum of the minimal supersymmetric standard model
Yoshiharu Kawamura, Tatsuo Kobayashi, Jisuke Kubo, Phys.Lett. B432 (1998) 108-113, 1997年10月24日
Assuming that the string inspired, universal sum rules for soft

supersymmetry-breaking terms, which have been recently found both in a wide

class of four-dimensional superstrings and in supersymmertic gauge-Yukawa

unified gauge models, are satisfied above and at the grand unification scale,

we investigate theirlow energy consequences and derive sum rules in the

superpartner spectrum of the minimal supersymmetric standard model., 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenological implications of moduli-dominant SUSY breaking
Yoshiharu Kawamura, Shaaban Khalil, Tatsuo Kobayashi, Nuclear Physics B, 502, 1-2, 37, 58, 1997年09月29日
We study moduli-dominated SUSY breaking within the framework of string models. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Further gauginos are lighter than sfermions. This non-universality has phenomenologically important implications. We investigate radiative electroweak symmetry breaking in the mass spectrum derived from moduli-dominated SUSY breaking, where the lightest chargino and neutralino are almost gauginos. Moreover, constraints from the branching ratio of b → sγ and the relic abundance of the LSP are also considered. The mass spectrum of moduli-dominated SUSY breaking is favorable to the experimental bound of the b → sγ decay decreasing its branching ratio. We obtain an upper bound for the gravitino mass from the cosmological constraint. © 1997 Elsevier Science B.V., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Phenomenological implications of moduli-dominant SUSY breaking
Y Kawamura, S Khalil, T Kobayashi, NUCLEAR PHYSICS B, 502, 1-2, 37, 58, 1997年09月
We study moduli-dominated SUSY breaking within the framework of string models. This type of SUSY breaking in general leads to non-universal soft masses, i.e. soft scalar masses and gaugino masses. Further gauginos are Lighter than sfermions. This non-universality has phenomenologically important implications. We investigate radiative electroweak symmetry breaking in the mass spectrum derived from moduli-dominated SUSY breaking, where the lightest chargino and neutralino are almost gauginos. Moreover, constraints from the branching ratio of b --> s gamma and the relic abundance of the LSP are also considered. The mass spectrum of moduli-dominated SUSY breaking is favorable to the experimental bound of the b --> s gamma decay decreasing its branching ratio. We obtain an upper bound for the gravitino mass from the cosmological constraint. (C) 1997 Elsevier Science B.V., ELSEVIER SCIENCE BV, 英語

"Anomalous" U(1) symmetry in orbifold string models
Tatsuo Kobayashi, Hiroaki Nakano, Nuclear Physics B, 496, 1-2, 103, 131, 1997年07月07日
"Anomalous" U(1) gauge symmetry with a Green-Schwarz anomaly cancellation mechanism is discussed in the orbifold construction of four-dimensional heterotic string models. Some conditions are given as criteria to have "anomalous" U(1) in orbifold string models. In particular, "anomalous" U(1) is absent if the massless twisted matter has no mixing between visible and hidden sectors or if a certain type of discrete symmetries are found. We then give a general procedure for classifying orbifold models with "anomalous" U(1) and for identifying the "anomalous" U(1) basis. We illustrate our procedure in Z3 and Z4 orbifold models. According to our procedure, the classification of "anomalous" U(1) can be reduced to classification in the absence of a Wilson line. We also discuss discrete symmetries left unbroken after the "anomalous" U(1) breaking. This includes a possible relation between "anomalous" U(1) and discrete R symmetries. © 1997 Elsevier Science B.V., Elsevier, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

Soft scalar-mass sum rule in gauge-Yukawa unified models and its superstring interpretation
Y Kawamura, T Kobayashi, J Kubo, PHYSICS LETTERS B, 405, 1-2, 64, 70, 1997年07月
It is shown that a certain sum rule for soft supersymmetry-breaking scalar masses, which has been recently found in a certain class of superstring models, is universal for gauge-Yukawa unified models. To explain this coincidence, we argue that the low-energy remnant of the target-space duality invariance in the effective supergravity of compactified superstrings can be identified with the (broken) scale invariance in gauge-Yukawa unified models, and that gauge-Yukawa unification which is indispensable for the sum rule to be satisfied follows from the matching of anomalies. (C) 1997 Published by Elsevier Science B.V., ELSEVIER SCIENCE BV, 英語

Notes on Curtright-Zachos Deformations of osp(1,2) and Super Virasoro Algebras
Naruhiko Aizawa, Tatsuo Kobayashi, Haru-Tada Sato, Int.J.Mod.Phys. A12 (1997) 5867-5883, 1997年06月25日
Based on the quantum superspace construction of $q$-deformed algebra, we

discuss a supersymmetric extension of the deformed Virasoro algebra, which is a

subset of the $q$-$W_{\infty}$ algebra recently appeared in the context of

two-dimensional string theory. We analyze two types of deformed super-Virasoro

algebra as well as their $osp(1,2)$ subalgebras. Applying our quantum

superspace structure to conformal field theory, we find the same type of

deformation of affine $sl(2)$ algebra., 機関テクニカルレポート，技術報告書，プレプリント等

異常なU(1)対称性をもつスーパーストリング理論からの低エネルギー定理(原標題は英語)
川村嘉春, 小林達夫, 素粒子論研究, 95, 1, A60-A61, A61, 1997年04月
素粒子論グループ 素粒子研究編集部, 日本語

Soft Scalar-Mass Sum Rule in Gauge-Yukawa Unified Models and Its Superstring Interpretation
Yoshiharu Kawamura, Tatsuo Kobayashi, Jisuke Kubo, Phys.Lett. B405 (1997) 64-70, 1997年03月14日
It is shown that a certain sum rule for soft supersymmetry-breaking scalar

masses, which has been recently found in a certain class of superstring models,

is universal for gauge-Yukawa unified models. To explain this coincidence, we

argue that the low-energy remnant of the target-space duality invariance in the

effective supergravity of compactified superstrings can be identified with the

(broken) scale invariance in gauge-Yukawa unified models, and that gauge-Yukawa

unification which is indispensable for the sum rule to be satisfied follows

from the matching of anomalies., 機関テクニカルレポート，技術報告書，プレプリント等

A string-inspired ansatz for quark masses and mixing
T Kobayashi, ZZ Xing, MODERN PHYSICS LETTERS A, 12, 8, 561, 571, 1997年03月
We propose a simple but realistic pattern of quark mass matrices at the string scale, which can be derived from orbifold models of superstring theory with no use of gauge symmetries. This pattern is left-right symmetric and preserves the structural parallelism between up and down quark sectors. Its phenomenological consequences on flavor mixing and CP-violation are confronted with current experiments at the weak scale by using the renormalization group equations in the framework of minimal supersymmetric standard model. We find that good agreement is achievable without fine-tuning., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

"Anomalous U(1) Symmetry in Orbifold String Models"(jointly worked)　　　　　　　　　　　　　　　
Nucl. Phys., B496, 103, 131, 1997年

A String-inspired Ansatz for Quark Masses and Mixing
Tatsuo Kobayashi, Zhi-zhong Xing, 1996年09月26日
We propose a simple but realistic pattern of quark mass matrices at the
string scale, which can be derived from orbifold models of superstring theory
with no use of gauge symmetries. This pattern is left-right symmetric and
preserves the structural parallelism between up and down quark sectors. Its
phenomenological consequences on flavor mixing and $CP$ violation are
confronted with current experiments at the weak scale by use of the
renormalization-group equations in the framework of the minimal supersymmetric
standard model. We find that good agreement is achievable without fine-tuning.

A String-inspired Ansatz for Quark Masses and Mixing
Tatsuo Kobayashi, Zhi-zhong Xing, Mod.Phys.Lett. A12 (1997) 561-572, 1996年09月26日
We propose a simple but realistic pattern of quark mass matrices at the

string scale, which can be derived from orbifold models of superstring theory

with no use of gauge symmetries. This pattern is left-right symmetric and

preserves the structural parallelism between up and down quark sectors. Its

phenomenological consequences on flavor mixing and $CP$ violation are

confronted with current experiments at the weak scale by use of the

renormalization-group equations in the framework of the minimal supersymmetric

standard model. We find that good agreement is achievable without fine-tuning., 機関テクニカルレポート，技術報告書，プレプリント等

Specific Scalar Mass Relations in SU(3)*SU(2)*U(1) Orbifold Model
Yoshiharu Kawamura, Tatsuo Kobayashi, Tohru Komatsu, 1996年09月25日
We study flat directions and soft scalar masses using a $Z_3$ orbifold model
with $SU(3) \times SU(2) \times U(1)$ gauge group and extra gauge symmetries
including an anomalous $U(1)$ symmetry. Soft scalar masses contain $D$-term
contributions and particle mixing effects after symmetry breaking and they are
parametrized by a few number of parameters. Some specific relations among
scalar masses are obtained.

Specific Scalar Mass Relations in SU(3)*SU(2)*U(1) Orbifold Model
Yoshiharu Kawamura, Tatsuo Kobayashi, Tohru Komatsu, Phys.Lett. B400 (1997) 284-294, 400, 3/4, 284, 294, 1996年09月25日
We study flat directions and soft scalar masses using a $Z_3$ orbifold model

with $SU(3) \times SU(2) \times U(1)$ gauge group and extra gauge symmetries

including an anomalous $U(1)$ symmetry. Soft scalar masses contain $D$-term

contributions and particle mixing effects after symmetry breaking and they are

parametrized by a few number of parameters. Some specific relations among

scalar masses are obtained., 機関テクニカルレポート，技術報告書，プレプリント等

Generic Formula of Soft Scalar Masses in String Models
Yoshiharu Kawamura, Tatsuo Kobayashi, 1996年08月06日
We derive formula of soft supersymmetry breaking scalar masses from
4-dimensional string models within a more generic framework. We consider
effects of extra gauge symmetry breakings including an anomalous $U(1)$
breaking through flat directions, that is, $D$-term and $F$-term contributions,
particle mixing effects and heavy-light mass mixing effects. Some
phenomenological implications are discussed based on our mass formula.

Generic Formula of Soft Scalar Masses in String Models
Yoshiharu Kawamura, Tatsuo Kobayashi, Phys.Rev. D56 (1997) 3844-3859, 56, 7, 3844, 3859, 1996年08月06日
We derive formula of soft supersymmetry breaking scalar masses from

4-dimensional string models within a more generic framework. We consider

effects of extra gauge symmetry breakings including an anomalous $U(1)$

breaking through flat directions, that is, $D$-term and $F$-term contributions,

particle mixing effects and heavy-light mass mixing effects. Some

phenomenological implications are discussed based on our mass formula., 機関テクニカルレポート，技術報告書，プレプリント等

Quasi Yukawa fixed point due to decoupling of SUSY particles
T Kobayashi, Y Yamagishi, PHYSICS LETTERS B, 381, 1-3, 169, 176, 1996年07月
We study effects of SUSY particle decouplings on a quasi fixed point (QFP) of Yukawa coupling. From renormalization group analysis it is shown that if the SUSY breaking scale M(S) is large (greater than or similar to 1 TeV), effects of decoupling of Higgsinos and squarks raise the top Yukawa QFP. Tnis tendency is enhanced in most cases of non-universal SUSY breaking. For the case of M(S) less than or similar to 1 TeV, the decoupling of gluinos lowers m(t)(QFP). We checked some parameter dependencies for the top Yukawa QFP. The bottom-top Yukawa unified case is also studied. When top quark mass is measured more precisely, some patterns of soft mass spectra could be excluded if a rather large initial top Yukawa coupling is realized by the underlying theory., ELSEVIER SCIENCE BV, 英語

Flat Directions in $Z_{2n}$ Orbifold Models
Yoshiharu Kawamura, Tatsuo Kobayashi, Nucl.Phys. B481 (1996) 539-576, 1996年07月01日
We study generic features related to matter contents and flat directions in

$Z_{2n}$ orbifold models. It is shown that $Z_{2n}$ orbifold models have

massless conjugate pairs, $R$ and $\overline R$, in certain twisted sectors as

well as one of untwisted subsectors. Using these twisted sectors, $Z_{2n}$

orbifold models are classified into two types. Conjugate pairs, $R$ and

$\overline R$, lead to $D$-flatness as $\langle R \rangle = \langle \overline R

\rangle \neq 0$. We investigate generic superpotentials derived from orbifold

models so as to show that this direction is indeed a flat direction., 機関テクニカルレポート，技術報告書，プレプリント等

Soft scalar masses in string models with anomalous U(1) symmetry
Y Kawamura, T Kobayashi, PHYSICS LETTERS B, 375, 1-4, 141, 148, 1996年05月
We obtain the low-energy effective theory from string models with anomalous U(1) symmetry. The feature of soft supersymmetry breaking scalar masses and some phenomenological implications are discussed. We show that it is, in general, difficult to keep the degeneracy and the positivity of squared soft scalar masses at the Planck scale., ELSEVIER SCIENCE BV, 英語

Implications of nonuniversal soft masses for gauge coupling unification
R Altendorfer, T Kobayashi, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 11, 5, 903, 920, 1996年02月
We study the gauge coupling unification of the minimal supersymmetric standard model with nonuniversal soft scalar and gaugino masses. The unification scale of the gauge couplings is estimated for nonuniversal cases. It is sensitive to the nonuniversality. It turns out that these cases can be combined with the assumption of string unification, which leads to a prediction of sin(2) theta(W)(M(Z)) and k(1), the normalization of the U(1)(Y) generator. String unification predicts that k(1) = 1.3-1.4. These values have nontrivial implications for string model building. Two-loop corrections are also calculated. Some of these cases exhibit a large discrepancy between experiment and string unification. We calculate string threshold corrections to explain the discrepancy., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

Quasi Yukawa Fixed Point due to Decoupling of SUSY Particles
Tatsuo Kobayashi, Yoshio Yamagishi, Phys.Lett. B381 (1996) 169-176, 1996年01月31日
We study effects of SUSY particle decouplings on a quasi fixed point (QFP) of

Yukawa coupling. From renormalization group analysis it is shown that if the

SUSY breaking scale $M_S$ is large ($\simg 1$TeV), effects of decoupling of

Higgsinos and squarks raise the top Yukawa QFP. This tendency is enhanced in

most cases of non-universal SUSY breaking. For the case of $M_S\siml 1$TeV, the

decoupling of gluinos lowers $m_t^{\rm QFP}$. We checked some parameter

dependencies for the top Yukawa QFP. The bottom-top Yukawa unified case is also

studied. When top quark mass is measured more precisely, some patterns of soft

mass spectra could be excluded if rather large initial top Yukawa coupling is

realized by underlying theory., 機関テクニカルレポート，技術報告書，プレプリント等

Soft Scalar Masses in String Models with Anomalous $U(1)$ symmetry
Yoshiharu Kawamura, Tatsuo Kobayashi, 1996年01月30日
We obtain the low-energy effective theory from string models with anomalous
$U(1)$ symmetry. The feature of soft supersymmetry breaking scalar masses and
some phenomenological implications are discussed. We show that it is, in
general, difficult to keep the degeneracy and the positivity of squared soft
scalar masses at the Planck scale.

Soft Scalar Masses in String Models with Anomalous $U(1)$ symmetry
Yoshiharu Kawamura, Tatsuo Kobayashi, Phys.Lett.B375:141-148,1996; ERRATUM-ibid.B388:867,1996, 1996年01月30日
We obtain the low-energy effective theory from string models with anomalous

$U(1)$ symmetry. The feature of soft supersymmetry breaking scalar masses and

some phenomenological implications are discussed. We show that it is, in

general, difficult to keep the degeneracy and the positivity of squared soft

scalar masses at the Planck scale., 機関テクニカルレポート，技術報告書，プレプリント等

"Flat Directions in Z_2n Orbifold Models", (jointly worked)
Nucl. Phys., B481, 539, 576, 1996年

Remarks on the Kielanowski parametrization of the Kobayashi-Maskawa matrix
Tatsuo Kobayashi, Zhi-Zhong Xing, Modern Physics Letters A, 11, 31, 2531, 2537, 1996年
We study the Kielanowski parametrization of the Kobayashi-Maskawa (KM) matrix V. A new two-angle parametrization is investigated explicitly and compared with the Kielanowski ansatz. Both of them are symmetric matrices and lead to |V13/V23| = 0.129. Necessary corrections to the off-diagonal symmetry of V are also discussed., World Scientific Publishing Co. Pte Ltd, 英語

"Quantum Deformed igl(n) Algebra on Quantum Space", (jointly worked)
Mod. Lett., 11, 7, 535, 543, 1996年

非普遍的な軟らかいSUSYの破れのもとでの準Yukawa固定点 (原標題は英語)
小林達夫, 山岸芳夫, 日本物理学会北陸支部・応用物理学会北陸・信越支部合同講演会講演予稿集, 1995, 18, 1995年12月
日本語

Neutron Electric Dipole Moment under Non-Universal Soft SUSY Breaking Terms((3).Susy phenomenology, SUSY GUT and SUSY Breaking Mechanism,YITP workshop(Particle physics and its future perspective))
小林 達夫, 紺村 昌彦, 末松 大二郎, 山田 聖典, 山岸 芳夫, 素粒子論研究, 92, 1, A46, 1995年10月20日
素粒子論グループ 素粒子研究編集部, 日本語

29a-SG-7 Quasi Yukawa Fixed Point Under Non-universal soft SUSY Breaking
小林 達夫, 山岸 芳夫, 日本物理学会講演概要集. 秋の分科会, 1995, 1, 14, 14, 1995年09月12日
一般社団法人日本物理学会, 英語

NEUTRON ELECTRIC-DIPOLE MOMENT UNDER NONUNIVERSAL SOFT SUSY BREAKING TERMS
T KOBAYASHI, M KONMURA, D SUEMATSU, K YAMADA, Y YAMAGISHI, PROGRESS OF THEORETICAL PHYSICS, 94, 3, 417, 433, 1995年09月
The electric dipole moment of the neutron (EDMN) is re-examined in the framework of non-universal soft supersymmetry breaking. We review some features of the relation between the EDMN and non-universal soft supersymmetry breaking terms. It is shown that the constraints on the soft scalar masses and soft CP phases have a rather strong dependence on the non-universality of soft breaking terms. We also show that the soft CP phase phi(B) which has no natural suppression mechanism may not contribute significantly to the EDMN in a certain parameter region where the radiative symmetry breaking occurs successfully. If this is the case, phi(B) may not need to be so small., KYOTO UNIV, 英語

非普遍的ソフトSUSY破れが存在する場合の準Yukawa固定点(原標題は英語)
小林達夫, 山岸芳夫, 日本物理学会講演概要集(分科会), 1995, Autumn Pt 1, 14, 14, 1995年09月
一般社団法人日本物理学会, 日本語

NONUNIVERSAL SOFT SCALAR MASSES IN SUPERSTRING THEORIES
T KOBAYASHI, D SUEMATSU, K YAMADA, Y YAMAGISHI, PHYSICS LETTERS B, 348, 3-4, 402, 410, 1995年04月
We study soft scalar masses in comparison with gaugino masses in 4-dimensional string models. In general non-universal soft masses are derived in orbifold models. We give conditions on modular weights which lead to a large non-degeneracy in the soft scalar mass spectrum. This non-universality is applied to the unification of gauge coupling constants in the minimal string model., ELSEVIER SCIENCE BV, 英語

29p-Y-13 Non-universal SUSY breaking effects on Radiative SU(2)×U(1)breaking
小林 達夫, 末松 大二郎, 山田 聖典, 山岸 芳夫, 日本物理学会講演概要集. 年会, 50, 1, 17, 17, 1995年03月16日
一般社団法人日本物理学会, 日本語

放射SU(2)×U(1)破れに対する非普遍SUSY破れの影響
小林達夫, 末松大二郎, 山田聖典, 山岸芳夫, 日本物理学会講演概要集(年会), 50th, 1, 17, 1995年03月
日本語

"Quark Mass Matrices in Orbifold Models"
Phys. Lett., 358, 3/4, 253, 258, 1995年

"Selection Rules for Nonrenormalizable Couplings in Superstring Theories"
Phys. Lett., 354, 3/4, 264, 270, 1995年

"CP in Orbifold Models", (jointly worked)
Phys. Lett., 343, 1/4, 122, 127, 1995年

"Minimal String Unification and Yukawa Couplings in Orbifold Models"
Int. J. Mod. Phys., 10, 10, 1393, 1411, 1995年

MINIMAL STRING UNIFICATION AND CONSTRAINT ON HIDDEN SECTOR
H KAWABE, T KOBAYASHI, N OHTSUBO, NUCLEAR PHYSICS B, 434, 1-2, 210, 230, 1995年01月
We examine whether a minimal string model possessing the same massless spectra as the MSSM can be obtained from Z(4), Z(6) and Z(8) orbifold constructions. Using an anomaly cancellation condition of the target space duality symmetry, we derive allowable values of a level k(1) of U(1)(Y) for the minimal string model on the orbifolds through computer analyses. We investigate threshold corrections of the gauge coupling constants of SU(3), SU(2) and U(1)Y and examine consistencies of the model with the LEP experiments. It is found that Z(4) and Z(8)-II cannot derive the minimal string model but Z(6)-I, Z(6)-II and Z(8)-I are possible to derive it with k(1) = 29/21, 1 less than or equal to k(1) less than or equal to 32/21 and 1 less than or equal to k(1) less than or equal to 41/21, respectively, We obtain explicitly allowed combinations of modular weights. The minimum values of the moduli on unrotated planes are estimated within the ranges of the levels. Further we investigate what kinds of hidden sectors are consistent with the minimal string models. Also their gauge coupling constants of the hidden groups are estimated, We discuss Yukawa couplings of the models., ELSEVIER SCIENCE BV, 英語

Superstring Unification and Soft SUSY Breaking Terms (弦理論と量子重力の課題)
小林 達夫, 素粒子論研究, 90, 3, C81, C85, 1994年12月20日
素粒子論グループ 素粒子研究編集部, 英語

超弦理論から標準模型へ(第22回北陸合宿研究会の報告,地域スクール報告)
小林 達夫, 素粒子論研究, 90, 2, B51, 1994年11月20日
素粒子論グループ 素粒子研究編集部, 日本語

超弦理論から標準模型へ
小林達夫, 素粒子論研究, 90, 2, B51, 1994年11月
日本語

非普遍性ソフトSUSYの破れ項目下の中性子電気双極子モーメント
小林達夫, 紺村昌彦, 末松大二郎, 山田聖典, 山岸芳夫, 日本物理学会北陸支部・応用物理学会北陸・信越支部合同講演会講演予稿集, 1994, 11, 1994年11月
日本語

Minimal String Unification in Orbifold Models (素粒子物理とその将来像)
小林 達夫, 素粒子論研究, 89, 4, D92, D94, 1994年07月20日
素粒子論グループ 素粒子研究編集部, 英語

GAUGE COUPLING UNIFICATION DUE TO NONUNIVERSAL SOFT SUPERSYMMETRY BREAKING
T KOBAYASHI, D SUEMATSU, Y YAMAGISHI, PHYSICS LETTERS B, 329, 1, 27, 32, 1994年06月
Gauge coupling unification is studied in the MSSM with non-universal soft supersymmetry breaking terms. If gaugino masses are sufficiently smaller than scalar soft masses and the scalar soft masses have also certain types of non-universality, the gauge coupling unification scale can be larger than 3 x 10(16) GeV even within the MSSM contents. String unification may not need a large threshold correction or a large modulus value. We also discuss the relation to the string model building., ELSEVIER SCIENCE BV, 英語

MINIMAL STRING UNIFICATION AND HIDDEN SECTOR IN Z(8) ORBIFOLD MODELS
T KOBAYASHI, PHYSICS LETTERS B, 326, 3-4, 231, 237, 1994年05月
We study the minimal supersymmetric standard model derived from the Z8 orbifold models and its hidden sectors. We use a target-space duality anomaly cancellation so as to investigate hidden sectors consistent with the MSSM unification. For the allowed hidden sectors, we estimate running gauge coupling constants making use of threshold connections due to higher massive modes. The calculation is important from the viewpoint of a gaugino condensation, which is one of the most promising mechanisms to break the supersymmetry., ELSEVIER SCIENCE BV, 英語

LEVELS OF U(1)Y IN MINIMAL STRING MODEL ON Z(N)XZ(M) ORBIFOLDS
H KAWABE, T KOBAYASHI, N OHTSUBO, PHYSICS LETTERS B, 325, 1-2, 77, 84, 1994年04月
We study a minimal string model possessing the same massless spectra as the MSSM on Z(N) x Z(M) orbifolds. Threshold corrections of the gauge coupling constants of SU(3), SU(2) and U(1)Y are investigated in a case of an overall modulus. Using computer analyses, we search ranges of levels of U(1)Y allowed by the LEP experiments. It is found that Z3 x Z3 can not derive the minimal string model for a M(Z) SUSY breaking scale. The minimum values of the overall moduli are estimated within the ranges of the levels., ELSEVIER SCIENCE BV, 英語

"Study of Minimal String Unification in Z₈ Orbifold Models", (jointly worked)
Phys. Lett., 322, 4, 331, 339, 1994年

GEOMETRICAL ASPECTS OF Z(N) ORBIFOLD PHENOMENOLOGY
T KOBAYASHI, N OHTSUBO, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 9, 1, 87, 125, 1994年01月
We study the geometrical and phenomenological aspects of Z(N) orbifold models. Conditions on-the background moduli and Wilson lines are clarified. We investigate the explicit Z(N)-invariant states through a modified GSO projection and calculate Yukawa coupling conditions due to space-group and SO(10) invariance. We estimate a contribution of a holomorphic instanton to the couplings., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

Differential Calculi on h-deformed Bosonic and Fermionic Quantum Planes
Tatsuo Kobayashi, Mod.Phys.Lett.A8:3741-3748,1993, 8, 39, 3741, 3748, 1993年08月10日
We study differential calculus on h-deformed bosonic and fermionic quantum

space. It is shown that the fermionic quantum space involves a parafermionic

variable as well as a classical fermionic one. Further we construct the

classical $su(2)$ algebra on the fermionic quantum space and discuss a mapping

between the classical $su(2)$ and the h-deformed $su(2)$ algebras., 機関テクニカルレポート，技術報告書，プレプリント等

THE Z(4)XZ(4) ORBIFOLD MODEL AT AN ENHANCEMENT POINT AND THE 2(6) MODEL
T KOBAYASHI, N OHTSUBO, K TANIOKA, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 8, 20, 3553, 3563, 1993年08月
We construct a ''shifted'' Z4 x Z4 orbifold model equivalent to a twisted Z4 X Z4 orbifold model at an enhancement point. It is proved that the N = 2 algebra of the 2(6) model is coincident with that of the ''shifted'' orbifold model. The correspondence between the Z4 x Z4 orbifold model and the 2(6) model is investigated with respect to massless spectra and Yukawa couplings. Also studied are Yukawa couplings and some other aspects of the models away from the enhancement point., WORLD SCIENTIFIC PUBL CO PTE LTD, 英語

Quantum deformed su(m/n) algebra and superconformal algebra on quantum superspace
Tatsuo Kobayashi, Zeitschrift für Physik C Particles and Fields, 60, 1, 101, 109, 1993年03月
We study a deformed su(m/n) algebra on a quantum superspace. Some interesting aspects of the deformed algebra are shown. As an application of the deformed algebra we construct a deformed superconformal algebra. From the deformed su(1/4) algebra, we derive deformed Lorentz, translation of Minkowski space, iso(2, 2) and its supersymmetric algebras as closed subalgebras with consistent automorphisms. © 1993 Springer-Verlag., Springer-Verlag, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

q-deformed superconformal algebra on quantum superspace
Tatsuo Kobayashi, Tsuneo Uematsu, Phys.Lett. B306 (1993) 27-33, 1993年02月15日
A quantum deformation of 4-dimensional superconformal algebra realized on

quantum superspace is investigated. We study the differential calculus and the

action of the quantum generators corresponding to $sl_q(1|4)$ which act on the

quantum superspace. We derive deformed $su(1|2,2)$ algebras from the deformed

$sl(1|4)$ algebra. Through a contraction procedure we obtain a deformed

super-Poincar{\'e} algebra., 機関テクニカルレポート，技術報告書，プレプリント等

"q-Deformed Superconformal Algebra on Quantum Superspace", (jointly worked)
Phys. Lett., 306, 1/2, 27, 33, 1993年

"q-Deformed Conformal and Poincar(]E85EE[) Algebras on Quantum 4-Spinors", (jointly worked)
Z. Phys., 58, 4, 559, 565, 1993年

q-deformed conformal and Poincar{é} algebras on quantum 4-spinors
Tatsuo Kobayashi, Tsuneo Uematsu, Z.Phys. C58 (1993) 559-566, 1992年10月30日
We investigate quantum deformation of conformal algebras by constructing the

quantum space for $sl_q(4,C)$. The differential calculus on the quantum space

and the action of the quantum generators are studied. We derive deformed

$su(4)$ and $su(2,2)$ algebras from the deformed $sl(4)$ algebra using the

quantum 4-spinor and its conjugate spinor. The 6-vector in $so_q(4,2)$ is

constructed as a tensor product of two sets of 4-spinors. The reality condition

for the 6-vector and that for the generators are found. The q-deformed

Poincar{\'e} algebra is extracted as a closed subalgebra., 機関テクニカルレポート，技術報告書，プレプリント等

2p-H-2 Differential Calculus on Quantum Superspace and Deformation of Phase Space
小林 達夫, 秋の分科会講演予稿集, 1992, 1, 2, 2, 1992年09月14日
一般社団法人日本物理学会, 日本語

量子超空間と位相空間の変形における微分学
小林達夫, 日本物理学会講演概要集(分科会), 1992, Autumn Pt 1, 2, 1992年09月
日本語

Moduli Space of Orbifold and Phenomenological Aspects
小林 達夫, 素粒子論研究, 85, 4, D3, D5, 1992年07月20日
素粒子論グループ 素粒子研究編集部, 日本語

オービフォールドのモジュラス空間と現象論的様相
小林達夫, 素粒子論研究, 85, 4, D3-D5, 1992年07月
日本語

Differential calculus on the quantum superspace and deformation of phase space
Tatsuo Kobayashi, Tsuneo Uematsu, Zeitschrift für Physik C Particles and Fields, 56, 2, 193, 199, 1992年06月
We investigate non-commutative differential calculus on the supersymmetric version of quantum space in which quantum supergroups are realized. Multiparametric quantum deformation of the general linear super-group, GLq(m|n), is studied and the explicit form for the {Mathematical expression} is presented. We apply these results to the quantum phase-space construction of OSpq(2n|2m) and calculate their {Mathematical expression}. © 1992 Springer-Verlag., Springer-Verlag, 英語, 機関テクニカルレポート，技術報告書，プレプリント等

"Shifted Z₆ Orbifold Models and 1・4 Model", (jointly worked)
Prog. Theor. Phys, 88, 2, 431, 442, 1992年

"Correspondence of Z₄×Z₄ Orbifold Model and 2⁶ Model"　　　　　　　　　　　　　　　
Suppl. Prog. Theor. Phys., 110, 277, 290, 1992年

ALLOWED YUKAWA COUPLINGS OF ZNXZM ORBIFOLD MODELS
T KOBAYASHI, N OHTSUBO, PHYSICS LETTERS B, 262, 4, 425, 431, 1991年06月
SO(10) momenta and fixed points are studied for obtaining non-vanishing Yukawa couplings of Z(N) x Z(M) orbifold models. As an example, we investigate explicity three-point couplings of Z4 x Z4 and Z3 x Z3 orbifolds with the standard embedding and no discrete torsion. Comparing with the 2(6) and 1(9) model by Gepner's coset construction, respectively, we find discrepancies with respect to the numbers of (27) (27) (27) couplings, while the numbers of 27 are identical., ELSEVIER SCIENCE BV, 英語

ANALYSES ON THE WILSON LINES OF ZN ORBIFOLD MODELS
T KOBAYASHI, N OHTSUBO, PHYSICS LETTERS B, 257, 1-2, 56, 62, 1991年03月
The Wilson lines of Z(N) orbifold models are studied. From analyses on the six-dimensional orbifolds, we obtain some features and restrictions on the Wilson lines, which are not found in the prime order orbifolds. Following the generalized GSO projection, the Z(N) invariant physical states are constructed. It is shown how to obtain all possible Z(N) orbifold models with Wilson lines., ELSEVIER SCIENCE BV, 英語

ZN ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, Y ONO, K TANIOKA, NUCLEAR PHYSICS B, 341, 3, 611, 640, 1990年09月
ELSEVIER SCIENCE BV, 英語

"Yukawa Coupling Condition of Z_N Orbifold Models", (jointly worked)　　　　　　　　　　　　　　　
Phys. Lett., B245, 441, 446, 1990年

Z8 AND Z12 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, Y ONO, K TANIOKA, PHYSICS LETTERS B, 227, 3-4, 381, 386, 1989年08月
ELSEVIER SCIENCE BV, 英語

GAUGE GROUPS OF ZN ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, K TANIOKA, PROGRESS OF THEORETICAL PHYSICS, 82, 1, 171, 182, 1989年07月
KYOTO UNIV, 英語

Z4 AND Z6 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, Y ONO, K TANIOKA, N OHTSUBO, PHYSICS LETTERS B, 218, 2, 169, 175, 1989年02月
ELSEVIER SCIENCE BV, 英語

Z7 ORBIFOLD MODELS
Y KATSUKI, Y KAWAMURA, T KOBAYASHI, N OHTSUBO, PHYSICS LETTERS B, 212, 3, 339, 342, 1988年09月
ELSEVIER SCIENCE BV, 英語

Localication of Heterotic Anomalies on Various Hyper Surfaces of T^6/Z_4　　　　　　　　　　　　　　　
Phys. Rev., D

An introduction to non-Abelian discrete symmetries for particle physicists
Ishimori Hajime, Kobayashi Tatsuo, Ohki Hiroshi, Okada Hiroshi, Shimizu Yusuke, Tanimoto Morimitsu
Springer-Verlag, 2012年, 9783642308048, 英語

Particle physics beyond the standard model : proceedings of the 16th Yukawa International Seminar (YKIS2008), January 26- March 25, 2009, Kyoto, Japan
Yukawa International, Symposium, 小林 達夫, Kugo Taichi
Progress of Theoretical Physics, 2009年, 英語

弦理論から導かれるフレーバー構造とその現象論的性質に関する研究
小林 達夫, 京都大学大学院理学研究科
[小林達夫], 2008年

湯川結合の階層構造を導き出す機構と超対称性の破れ
小林 達夫, 京都大学大学院理学研究科
[小林達夫], 2004年

Zn軌道体模型の幾何学的, 現象論的性質
小林 達夫
小林達夫, 1991年, 日本語

湯川結合とコンパクト空間
科学研究費助成事業
2019年04月01日 - 2021年03月31日
小林 達夫
本研究の目的は、超弦理論のコンパクト化の幾何学を起源として現れるクォーク・レプトンのフレーバー構造の探求である。特に、トーラスやオービフォルド空間がもつモジュラー対称性の解析を行い、背景磁場のあるもつコンパクト空間上のゼロモードの変換性を解析し、その対称性の有限部分群が、A4,S4やその拡張された群がフレーバー対称性となっていることを示した。特に、３世代模型を系統的に分類し、そのフレーバー対称性や湯川行列のパターン等の分類を行った。そして、具体的に、いくつかのコンパクト化の模型において、クォークの質量や混合角などの実験値の導出を可能性を調べた。また、このような実験値を再現するのに重要なパラメータがモジュライ場の真空期待値の値である。その値の決定は、長年、モジュライ固定の問題として認識されていた課題である。モジュライの真空期待値を決定を様々な3-formフラックスをもつコンパクト化において、系統的に行い、どのような値が実現可能か、そのときにCP対称性が自発的に破れる可能性はあるかなどを詳細に調べた。さらにカラビーヤウ多様体上のフレーバー構造やCP対称性の自発的破れなども研究を行った。
そのようなトップダウン的なアプローチの一方で、ボトムアップアプローチとして、モジュラー対称性の有限部分群をフレーバー対称性としてもつ模型の構築や質量や混合角などの実験値の再現する模型を議論し、現在の実験での制限や将来実験への予言等について解析を行った。
日本学術振興会, 新学術領域研究(研究領域提案型), 北海道大学, 19H04605

超弦理論におけるモジュライの物理について
科学研究費助成事業
2017年04月01日 - 2019年03月31日
小林 達夫
本研究の目的は、コンパクト空間上の超弦理論の研究であり、その理論特有のモジュライの素粒子物理学的意味合いの研究である。コンパクト空間やモジュライが関わる物理現象を探求していくことは、コンパクト空間上の超弦理論の間接的な検証へつながる。
本年度は、特にトーラスやオービフォルドがもつ幾何学的対称性に注目し、そのようなコンパクト空間上上のD-ブレーン模型のゼロモードが示す対称性を系統的に解析した。そのような対称性は世代間を変換させるような離散的なフレーバー対称性であることを示した。この対称性は、従来のフレーバー対称性と異なり、湯川結合なども変換するような大尉焼成である。さらに、モジュラー群の有限部分群の下で非自明に変換するモジュラー形式の多重項の新たな構成法を見出した。
上述のような超弦理論における成果を踏まえて、場の理論のフレーバーに関する模型の構築も行った。従来、クォーク・レプトンの３世代にフレーバー対称性を課し、その対称性を新たに導入したスカラー場の真空期待値で破ることで、クォーク・レプトンの質量や混合角を導出することが、盛んになされてきた。新しい模型構築のアプローチとして、上述のモジュラー対称性の有限部分群を仮定し、３世代のクォーク・レプトンにその表現をアサインし、なおかつ、湯川結合や右巻きニュートリのマヨラナ質量もその有限部分群の非自明表現となるモジュラー形式であると仮定し、クォーク・レプトンのフレーバーの模型構築を行った。このアプローチは、新たに対称性を破るスカラー場の導入が必要なく、その点では、ミニマルなフレーバー模型となっている。また、コンパクト空間の幾何学的対称性とフレーバー対称性が関連付けられ、クォーク・レプトンの質量と混合角が導出されるので、非常に注文を集めている。
日本学術振興会, 新学術領域研究(研究領域提案型), 北海道大学, 17H05395

隠れたセクターの場や粒子が引き起こす多様な宇宙現象を用いた究極理論探査
科学研究費助成事業
2014年06月27日 - 2018年03月31日
小玉 英雄, 井岡 邦仁, 吉野 裕高, 郡 和範, 高橋 史宜, 檜垣 徹太郎, 中山 和則, 小林 達夫, 早田 次郎, 溝口 俊弥, 住友 洋介, 野澤 真人
超弦理論と呼ばれる統一理論が，自然の最も根源的な基本法則であるかどうかを，理論の予言する非常に弱い相互作用をする場や粒子が引き起こす特有の宇宙現象の観測により検証する方策を組織的に探査した．成果として，アクシオンと呼ばれるスカラ場とブラックホールの相互作用から生じる重力波の観測，高エネルギー天体からのガンマ線と赤外線背景放射の観測，アクシオンダークマターを通過する電磁波や重力波の観測，加速器における新粒子探査，宇宙初期インフレーションのCMBによる観測など様々な検証法を提案した．さらに，素粒子標準模型および宇宙現象の双方を整合的に記述する可能性のある超弦理論の例をいくつか具体的に構成した．
日本学術振興会, 基盤研究(A), 26247042

標準模型を越えて統一理論へ
科学研究費助成事業
2012年04月01日 - 2015年03月31日
九後 太一, 谷本 盛光, 久保 治輔, 小林 達夫, 前川 展祐
クォークとレプトンの間で対照的な階層的世代間混合構造を手がかりとして、標準模型を越えた所に想定される素粒子の統一理論を探求することを目的として、
（1）全国にまたがる研究代表者・分担者達がそれぞれの分担課題を個別に研究して研究成果を上げた。特に、混合構造の背後に超弦理論の示唆する離散的対称性やE6ゲージ対称性が隠れている可能性が大きいことを明らかにした。
（2）また、毎年一回Summer Instituteを企画・組織し、全国の研究者（特に若手）の、国内およびアジアでの国際的な、実り多い共同研究・研究協力を推進することができた。
日本学術振興会, 基盤研究(B), 24340049

現実的な超弦理論の低エネルギー有効理論とその対称性について
科学研究費補助金(基盤研究(C))
2013年 - 2015年
小林 達夫
II型超弦理論やヘテロ型弦理論から標準模型を再現するコンパクト化の研究を行い、スぺクトにおいて現実的な模型を多く構築した。それらの模型においてゲージ結合は実験値を再現するか、質量行列は現実的かなど定量的な解析も行い、標準模型を再現する研究を推進した。それらの定量的な解析においては、摂動論的に計算できる範囲と非摂動論的計算を具体的に行った解析も含む。
そのような素粒子現象論的性質の解明に加えて、インフレーションやダークマターやその他の超弦理論から導かれる宇宙論的性質の解明についても研究を行い、あらたインフレーション模型の提案や新たな熱史の可能性を指摘した。
文部科学省, 基盤研究(C), 京都大学, 研究代表者, 競争的資金, 25400252

アクシオン型モジュライの引き起こす多様な宇宙現象をもちいた余剰次元探査
科学研究費助成事業
2010年04月01日 - 2014年03月31日
小玉 英雄, 太田 信義, 高橋 史宜, 中山 和則, 太田 信義, 柴田 大, 溝口 俊弥, 小林 達夫, 早田 次郎, 郡 和範, 石橋 明浩, 井岡 邦仁, 高橋 史宜, 吉野 裕高, 野澤 真人, 永田 竜, 川中 宣太, 富沢 真也
究極理論への新たな実験観測ウインドウの開拓を目指して，宇宙物理現象論と超弦理論・超重力理論の双方からアクシオンについて組織的な研究を行い，200編を超える論文を発表した．主な成果は，回転ブラックホールの引き起こすアクシオンボーズノバ現象の数値シミュレーションによる実証とその重力波による観測可能性の発見，高エネルギーガンマ線観測と赤外線放射観測の矛盾をアクシオンにより解消するパラメータの導出，重いモジュライの崩壊により生成されたアクシオンの宇宙背景放射への影響の評価とそれによる余剰空間コンパクト化への制限，アクシオン起源の等曲率ゆらぎや位相的励起生成に基づく素粒子模型への制限の導出などである．
日本学術振興会, 基盤研究(A), 大学共同利用機関法人高エネルギー加速器研究機構, 22244030

素粒子の世代の起源と大統一理論
科学研究費助成事業
2008年 - 2011年
九後 太一, 谷本 盛光, 久保 治輔, 寺尾 治彦, 小林 達夫, 前川 展祐, 坂東 昌子
クォークとレプトンの間の対照的な階層的世代間混合構造をヒントとして、標準模型を超えたところに想定される素粒子の大統一理論を探究することを目的として、(1)全国にまたがる研究代表者・分担者達がそれぞれの分担課題を個別に研究して研究成果を上げた。(2)また、毎年一回宿泊型Summer Instituteを企画・組織し、この研究分野の研究者を全国的にかつ有機的に組織し、実り多い共同研究・研究協力を推進することができた。
日本学術振興会, 基盤研究(B), 京都大学, 20340053

超弦理論の現象論的性質についての研究
科学研究費補助金(基盤研究(C))
2008年 - 2011年
小林 達夫
超弦理論から導かれる4次元低エネルギー有効理論の研究を行った。超弦理論から標準模型を導出するのに有望と思われるオービファルド上のヘテロ型弦理論と背景磁場をもつブレーン模型を出発点にその4次元低エネルギー有効理論の解析を行った。特に、その有効理論に現れる離散対称性を調べ、特定の非可換離散フレーバー対称性が現れることを示した。そして離散対称性のアノマリーに関しても普遍的な関係式があることを示した。さらに、弦理論の振幅の計算を行い、場の理論の対称性の言葉では簡単に理解することができない弦理論特有の結合の選択則があることをしめした。
文部科学省, 基盤研究(C), 京都大学, 研究代表者, 競争的資金, 20540266

弦理論のコンパクト化と現象論的性質についての研究
科学研究費助成事業
2008年 - 2010年
小林 達夫, CHOI Kang-Sin
超弦理論は、重力を含む統一理論の有力な候補である。超弦理論が本当に素粒子物理として、意味がある理論であるならば、低エネルギー有効理論として標準模型を再現するはずである。本研究の目的は、素粒子物理学の様々な現象論的性質が超弦理論の枠組みからどのようにして導出されるのかを研究することである。本年度我々は、まずF理論の現象論への応用について研究を行った。F理論は、IIB型超弦理論の強結合理論を記述すると思われているが、最近そのF理論の現象論への応用が盛んに研究されている。これまでのF理論の模型構築のシナリオはE8群から一度SU(5)群等の大統一理論を経て、標準模型を導出するようなアプローチであった。本年度我々は、SU(5)等の大統一理論を経るのではなく、直接標準模型を構築するような可能性を試み、かなり現実的なスペクトルを得ることに成功した。今後は、そのような研究を更に進めて、我々が構築した模型の質量行列や陽子崩壊、超対称性の破れなどの現象論的な性質の解析をする計画である。一方で我々は、背景磁場のあるブレーン模型の現象論的性質、特にフレーバー構造についての研究を行った。その結果によるとこのような模型では特定の非可換離散群がフレーバー対称性として現れることを示した。その起源は、コンパクト空間の幾何学的対称性ともともと大きなゲージ対称性が背景磁場のために破れる際に残った離散対称性の組み合わせであることを示した。今後はこの解析の結果を生かし、現実的なクォーク・レプトンの質量行列を導出する研究を行う予定である。
日本学術振興会, 特別研究員奨励費, 京都大学, 08F08326

素粒子模型構築へのLHC実験のインパクト
科学研究費助成事業
2004年 - 2009年
野尻 美保子, 小林 達夫, 前川 展裕
LHC実験では標準模型を越える粒子が生成され、その崩壊が観測されると期待されている。このような模型の中でも、超対称模型に代表される暗黒物質の候補ををもつ模型についてLHC実験によって、新粒子の質量・相互作用を測定する方法について研究を行い、MT2の活用、end pointに寄らない質量決定法、Initial state radiationの除去法等について成果をあげた。
日本学術振興会, 特定領域研究, 16081207

弦理論から導かれるフレーバー構造とその現象論的性質に関する研究
科学研究費補助金(基盤研究(C))
2005年 - 2007年
小林 達夫
この研究の目的は、超弦理論のどのようなフレーバー構造が導出できるかを研究し、そのフレーバー構造に関する現象論的な性質を明らかにすることであった。現実的な湯川行列を導くために場の理論の模型として、離散的なnon-Abelianフレーバー対称性が最近注目されている。その起源については4次元の場の理論の立場からは、明らかではない。平成18年度に我々は、ヘテロ型オービフォルド模型において、コンパクト空間の幾何学的構造がこの離散的なnon-Abelianフレーバー対称性の起源になる可能性を示し、この4次元弦模型から導くことが可能な離散的なnon-Abelianフレーバー対称性を分類した。その典型的な対称性は、D4,Δ(54)などである。平成19年度では、D4フレーバー対称性のもとで、どのようなクォーク、レプトンの現実的な質量行列が導出可能なのかを研究した。更に、超対称性理論の枠組みでは、フレーバー対称性はクォーク、レプトンの質量行列を支配するのみでなく、そのスーパーパートナーであるスクォーク、スレプトンの質量行列(超対称性の破れの項)をも制限し、将来の加速器で検証できる可能性のある予言を与える。そのようなスーパーパートナーの質量行列の特徴的なパターンについて解析を行った。その他、湯川結合を含む高次の結合項のモジュライ依存性の計算の研究やモジュライの値の決定機構、およびそれにともなう超対称性の破れとその現象論的な効果についての研究を行った。
文部科学省, 基盤研究(C), 京都大学, 研究代表者, 競争的資金, 17540251

余次元世界と素粒子統一理論
科学研究費助成事業
2004年 - 2007年
九後 太一, 柳田 勉, 坂東 昌子, 谷本 盛光, 小林 達夫, 前川 展祐
研究代表者の九後は、分担者の坂東昌子氏らと共に、5次元超重力理論を用いてペンタクォークなどの新しいクォーク多体の束縛状態を考察し、その質量の計算方法を導出した。またスピン1/2のモノポールフェルミ粒子および電子の電気双極子モーメントおよび磁気モーメントを計算した。
坂東は、さらに分担者の谷本と共同で、ニュートリノの質量行列をゼロ構造を持つ対称行列の範囲で、大統一理論を用いてクォークとレプトンを統一的に説明できる可能性を研究した。
谷本は、さらに、種々な離散対称性を世代やフレーバー対称性として持つモデルを考案し、現実のクォーク・レプトンの混合・質量構造を説明するモデルを提案した。
柳田は、宇宙のバリオン数生成が大きな質量を持つマヨラナ型フェルミオンの崩壊を通して起こるというレプジェネシスの理論を提案し、そのシナリオと種々な統一理論の諸問題との整合性を研究し、レプジェネシスについてのレビューを書いた。
小林は、超弦理論から導かれるフレーバー構造の系統的な解析を始めた。モジュライ場の真空期待値の決定機構や、それから導かれる超対称性の破れや、質量構造など現象論的性質の研究を行った。
前川は、「E6×世代対称性」模型において、CP対称性を自発的に破ることで、小林-益川位相を導出できるだけでなく、深刻な超対称性CP問題をも解決できることを明らかにした。またanomalous U(1)が存在している大統一理論が少しの変形で超対称性が自発的に破れる模型になることを示した。
杉本は、酒井忠勝氏と共同で、超弦理論に基づくholographic QCD模型を考案し、現実のハドロンの諸性質をうまく再現し、現実世界の解析に有用な模型になっていることを示した。
この研究計画のもう一つの大きな目的-この研究分野の全国的な共同研究・研究協力の核としての宿泊型Summer Institute(SI)を企画・組織し、毎年開催すること-も、この4年間しっかり実行した。2006年には韓国で開催するなど、アジアを中心とした国際的共同研究の核にもなりつつある。
日本学術振興会, 基盤研究(B), 京都大学, 16340071

現実的湯川行列を導く機構とその超対称性の破れの項への影響
科学研究費補助金(特定領域研究)
2004年 - 2005年
小林 達夫
今年度は、超弦理論から導かれるフレーバー構造についての研究を行いました。超弦理論は、重力相互作用を含んだ統一理論の有力な候補です。そしてその弦理論は、我々の4次元時空以外に6次元コンパクト空間の存在を予言します。このコンパクト空間の幾何学的性質がフェルミオンのフレーバー構造を決定しています。しかし、これまではどのようなフレーバー構造が弦模型から導けるのか、どのようなパターンの湯川行列が導けるかといったことの系統的な解析はなされていませんでした。今年度は、heterotic Z6 orbifold models, intersecting D-brane modelsにおいて、そのような系統的な解析の第一歩を踏み出しました。前者についは現実的なquark/lepton質量行列が得られる可能性があるものの、後者の単純な模型では現実的な質量行列を導くことが難しいことが分かりました。さらに、上述のような弦模型の枠組みでは、湯川結合の強さ自体は、コンパクト空間の大きさや形を決めるようなモジュライ場の真空期待値の関数として与えられます。そしてその値が適当な値になったときに、現実的な質量行列が得られるわけです。したがって、モジュライの真空期待値の決定機構は、非常に重要です。このような目的で今年度はモジュライの真空期待値の様々な決定機構について研究しました。さらに、その際現れる超対称性の破れについても研究をしました。
文部科学省, 特定領域研究, 京都大学, 研究代表者, 競争的資金, 16028211

湯川結合の階層構造を導き出す機構と超対称性の破れ
科学研究費補助金(基盤研究(C))
2002年 - 2003年
小林 達夫
Quark, Leptonの質量や混合角の起源を探ることは、素粒子論の中で重要な課題の1つです。また、超対称模型の枠組みでは、現実的な湯川行列を生み出す機構は、超対称性の破れの項への影響を考えながら議論すべきです。更に、超対称性の破れの項については、フレーバー間の縮退度に関して大きな実験的制限があります。上述のようなことを踏まえ、縮退したsfermionの質量を導きつつ湯川結合の階層構造を与えるような模型を研究しました。まず、超対称標準模型に加えて超共形固定点をもつようなSCセクターのある模型を研究しました。この超共形ダイナミックスがquark, leptonに大きなanomalous dimensionを生成するので、この模型では湯川結合の階層構造を出しつつ、縮退したsfermion質量を導くことが可能です。また、似たような結果を導く別の模型としては、余剰次元がwarp背景幾何上の模型を研究しました。この模型では、湯川結合の階層構造の生成に役立つのは、5次元bulk massによる、bulk場の局在化です。更に、ラディオンにより超対称性の破れが起る場合には、フレーバー問題も改善されることが分かりました。また世代間にS_3離散対称性を課すような模型を調べました。このような対称性はこれまで提案されてきましたが、我々の模型の新しい点はHiggsセクターにもこの対称性を課せるようにHiggsセクターを拡張した点で、そのため、超対称性の破れの項もこのような対称性をもつと仮定でき、FCNCへの効果を実験の制限程度に下げることに役立ちます。更に、弦理論の枠内で湯川結合の計算をしました。特に、興味があるのはorbifold模型で、なぜなら階層的な湯川結合が導けることが知られているからです。これまで代表的なmoduliへの依存性は分かっていましたが、今回我々は様々なmoduliへの依存性を計算しました。我々の結果の中で、現象論的に重要なことの1つは、湯川結合での物理的なCPの破れに関しては、ある特定のmoduliしか関与しないことを示した点です。
文部科学省, 基盤研究(C), 京都大学, 研究代表者, 競争的資金, 14540256

ニュートリノ振動をめぐる理論的諸問題
科学研究費助成事業
2000年 - 2003年
九後 太一, 前川 展祐, 小林 達夫, 川崎 雅裕, 波場 直之
今年度の研究実績は次の通りである。
九後は、二つの仮定1)クォーク・レプトンの質量行列が、異常U(1)電荷φ_iにより冪が与えられる因子化された形λ^{φ_i+φ_j}(Frogatt-Nielsen形)をとること、および2)このU(1)電荷φ_iがSU(5)GUTの構造を持つこと、を置くだけで、先ず、up型、down型クォークの質量データが必然的にレプトン側の牧-中川-坂田(MNS)混合行列U_{MNS}の大きな2-3混合を意味していることを示した。さらに太陽と大気ニュートリノの二乗質量差の比のデータをインプットすれば、1-2混合もまた必ず大きくなるということ、すなわちbi-large混合を導くことを示した。
川崎は、宇宙背景放射の精密観測(WMAP)の結果から導かれた宇宙のバリオン密度と宇宙の軽元素合成理論から導かれるバリオン密度が有意にずれていることを説明できるシナリオをレプトン数の非対称や元素合成後のバリオン数の増大等を導入することによって作った。さらに、それを具体的に実現するものとして超対称性理論におけるQボール生成に基づくモデルを提案した。
小林は、dilaton moduli場の素粒子の翼象論への重要な役割として、湯川結合の様々なmoduliへの依存性を計算した。そして4次元有効理論の結合の大きさを決める様々なdilaton moduli場の真空期待値の決定の機構を研究し、これらのmoduli場のインフレーション時での振舞いを調べた。
前川は、異常U(1)を用いた大統一理論の研究を継続し、E_6におけるdoublet-triplet splittingを実現するよりシンプルなモデルを提唱しただけでな、doublet-triblet splittingを実現するため昔提唱されたsliding singlet機構を一般化した。また、E_6大統一理論においては、レプトンセクターの混合角が一般的にクォークセクターの混合角よりも大きくなることを指摘し、その同じ構造がホリゾンタル対称性導入によるFCNCのsuppressionを自然に実現することを指摘した。また、ホリゾンタル対称性を持つE_6のヒッグズセクターを構築した。
日本学術振興会, 特定領域研究, 京都大学, 12047214

超対称性の破れと超弦理論の現象論的性質　　　　　　　　　　　　　　　
競争的資金

Supersymmetry Breaking and Superstring Phenomenology　　　　　　　　　　　　　　　
競争的資金