Researcher Database

KOBAYASHI Tatsuo
Faculty of Science Physics Nonlinear Physics
Professor

Researcher Profile and Settings

Affiliation

  • Faculty of Science Physics Nonlinear Physics

Job Title

    Professor

Research Interests

  • FCNC   Leptogenesis   

Research Areas

  • Physics / Particle/Nuclear/Cosmic ray/Astro physics
  • Physics / Particle/Nuclear/Cosmic ray/Astro physics

Education

  •        - 1991  Kanazawa University  Graduate School, Division of National Science and Technology
  •        - 1986  Saitama University  Faculty of Science

Research Activities

Published Papers

Books etc

  • 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 9783642308048
  • 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

MISC

  • Junichiro Kawamura, Tatsuo Kobayashi, Natsumi Nagata  2018/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Naoya Omoto, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi  2018/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Takaaki Nomura, Hiroshi Okada  Phys. Rev. D 98, 055025 (2018)  2018/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Satoshi Nagamoto, Shintaro Takada, Shio Tamba, Takuya H. Tatsuishi  Phys. Rev. D 97, 116002 (2018)  2018/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi  Phys. Rev. D 97, 106006 (2018)  2017/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kenji Kadota, Tatsuo Kobayashi, Akane Oikawa, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi  2016/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano, Takuya H. Tatsuishi  Phys. Rev. D 94, 126020 (2016)  2016/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the flavor structure in $SO(32)$ heterotic string theory on six-dimensional torus with magnetic fluxes. In particular, 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.
  • Kei Hagimoto, Tatsuo Kobayashi, Hiroki Makino, Ken-ichi Okumura, Takashi Shimomura  2015/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 (1 TeV 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.
  • Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto, Yoshiyuki Tatsuta  Nucl.Phys. B894 (2015) 374-406  2015/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yuta Hamada, Tatsuo Kobayashi, Atsushi Ogasahara, Yuji Omura, Fumihiro Takayama, Daiki Yasuhara  JHEP10(2014)183  2014/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Naoya Omoto, Hajime Otsuka, Takuya H. Tatsuishi  Phys. Rev. D 96, 046004 (2017)  2017/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Shohei Uemura  Phys. Rev. D 96, 026019 (2017)  2017/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Akane Oikawa, Naoya Omoto, Hajime Otsuka, Ikumi Saga  Phys. Rev. D 95, 063514 (2017)  2016/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yukihiro Fujimoto, Tatsuo Kobayashi, Kenji Nishiwaki, Makoto Sakamoto, Yoshiyuki Tatsuta  Phys. Rev. D 94, 035031 (2016)  2016/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    Based on the result of classification in our previous work, 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 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 ($m_{\text{up}}/m_{\text{top}} \sim 10^{-5}$) on the complicated magnetized orbifolds $T^{2}/Z_{N}\,(N=3,4,6)$.
  • Kensuke Akita, Tatsuo Kobayashi, Akane Oikawa, Hajime Otsuka  2016/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto  Phys. Rev. D 92, 103518 (2015)  2015/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We consider domain walls in the $Z_3$ symmetric NMSSM. 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 moduli, gravitino, LSP and axion.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano, Takuya H. Tatsuishi  2015/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study $SO(32)$ heterotic string theory on torus with magnetic fluxes. Non-vanishing fluxes can lead to non-universal gauge kinetic functions for $SU(3) \times SU(2) \times U(1)_Y$ which is the important features of $SO(32)$ heterotic string theory in contrast to the $E_8\times E_8$ theory. It is found that the experimental values of gauge couplings are realized with ${\cal O}(1)$ values of moduli fields based on the realistic models with the $SU(3) \times SU(2) \times U(1)_Y$ gauge symmetry and three chiral generations of quarks and leptons without chiral exotics.
  • Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto  2014/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Yoshiyuki Tatsuta  Phys. Rev. D 90, 105006 (2014)  2014/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 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.
  • Tatsuo Kobayashi, Kentaro Tanaka, Takuya H. Tatsuishi  Phys. Rev. D 98, 016004 (2018)  2018/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Nana Geraldine Cabo Bizet, Tatsuo Kobayashi, Damian Kaloni Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala  2013/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study discrete R-symmetries, which appear in 4D low energy effective field theory derived from hetetoric orbifold models. We derive the R-symmetries directly from geometrical symmetries of 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. Surprisingly, for the cases covered by earlier explicit computations, the R-charges differ from the previous result. We study the anomalies associated with these R-symmetries, and comment on the results.
  • Kenji Kadota, Tatsuo Kobayashi, Ikumi Saga, Keigo Sumita  2018/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto, Yuya Yamaguchi  JCAP10 (2014) 025  2014/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study parameter space in the axion monodromy inflation corrected by dynamically generated terms involving with the axion. The potential has the linear potential 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 $r_T \sim 0.16$ and to a large negative running of spectral index $\alpha_s \sim - (0.02 -0.03)$. 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.
  • Kenji Kadota, Tatsuo Kobayashi, Keigo Sumita  2017/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 K\"ahler 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.
  • Tatsuo Kobayashi, Shohei Uemura, Junji Yamamoto  Phys. Rev. D 96, 026007 (2017)  2017/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We investigate the axion inflation model derived by poly-instanton effects in type II superstring theories. Poly-instanton effects are instanton effects corrected by another instanton and it 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 non-perturbative effects. From the view point of the cosmic inflation, such potential is interesting. In this paper, we numerically study the possibilities for realizing the cosmic inflation. We also study their spectral index and other cosmological observables, numerically.
  • Tatsuo Kobayashi, Yuji Omura, Osamu Seto, Kazuki Ueda  2017/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Osamu Seto, Takuya H. Tatsuishi  2017/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kensuke Akita, Tatsuo Kobayashi, Hajime Otsuka  JCAP 04(2017)042  2017/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tomo-hiro Abe, Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto  JHEP01(2014)065  2013/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita, Yoshiyuki Tatsuta  Phys. Rev. D 95, 015005 (2017)  2016/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 (VEVs) 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 VEVs which restore the supersymmetry but yield lepton number violating terms below the compactification scale, and show their phenomenological consequences.
  • Tatsuo Kobayashi, Kenji Nishiwaki, Yoshiyuki Tatsuta  JHEP 1704 (2016) 080  2016/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the CP-violating phase of the quark sector in the $U(8)$ flavor model 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. 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 $\delta_{\rm CP}$. In cases of multiple Higgs doublets emerging 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 $\delta_{\rm CP}$ can be simultaneously realized.
  • Tatsuo Kobayashi, Satoshi Nagamoto, Shohei Uemura  2016/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Osamu Seto, Takashi Shimomura, Yuko Urakawa  Mod. Phys. Lett. A, Vol. 32, No. 27 (2017) 1750142  2016/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $\ll m_{\phi} \lesssim 10^4$ eV. We also find that a strong correlation between the Hubble parameter at the relaxion stabilization and the scale $\Lambda$ of non-QCD strong dynamics, which generates the non-perturbative relaxion cosine potential. For a higher relaxion mass, a large scale $\Lambda$ becomes available. However, for its lower mass, $\Lambda$ should be small and constructing such a particle physics model is challenging.
  • Hiroyuki Abe, Tatsuo Kobayashi, Keigo Sumita  2016/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $SU(N_C)$ 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.
  • Tatsuo Kobayashi, Daisuke Nitta, Yuko Urakawa  2016/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino  2016/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Yoshiyuki Tatsuta, Shohei Uemura  Phys. Rev. D 93, 065029 (2016)  2015/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study effects of D-brane instantons wrapping rigid cycles on Z2*Z2' 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 has a possibility to explain observed mixing angles. We also compute the mu-term matrix among more than one pairs of Higgs fields induced by rigid D-brane instantons.
  • Tatsuo Kobayashi, Akane Oikawa, Hajime Otsuka  Phys. Rev. D 93, 083508 (2016)  2015/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We propose a new type of axion inflation with complex structure moduli in the framework of type IIB superstring theory compactified on 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 mirror Calabi-Yau manifold. The axionic shift symmetry is broken down to the discrete one by the inclusion of instantonic correction and certain three-from fluxes. Our proposed inflation scenario is compatible with K\"ahler moduli stabilization. We also study a typical reheating temperature in the case of complex structure moduli inflation.
  • Kenji Kadota, Tatsuo Kobayashi, Hajime Otsuka  2015/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Yuji Omura, Fumihiro Takayama, Daiki Yasuhara  2015/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hironori Hattori, Tatsuo Kobayashi, Naoya Omoto, Osamu Seto  Phys. Rev. D 92, 023517 (2015)  2015/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka, Yasufumi Takano  JHEP 1509 (2015) 056  2015/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Yoshiyuki Tatsuta, Shohei Uemura  Phys. Rev. D 92, 026001 (2015)  2015/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the mu-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 mu-term matrix has a certain permutation symmetry and its eigenvalues have large hierarchical structure without fine tuning.
  • Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino  2014/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 K\"ahler 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.
  • Tatsuo Kobayashi  2015/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the next-to-minimal supersymmetric standard model with the TeV scale mirage mediation. The 125 GeV Higgs boson mass is realized with O(10)% tuning for 1.5 TeV gluino and 1TeV stop masses.
  • Tatsuo Kobayashi, Satoshi Nagamoto  Phys. Rev. D 96, 096011 (2017)  2017/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 wavefunctions 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 $\lfloor M/N \rfloor +1$ except one case on the $T^2/Z_3$ orbifold.
  • Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino  2015/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $U(1)^2 \rtimes S_3$ symmetry.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka  JHEP 1504 (2015) 160  2014/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 K\"ahler 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.
  • Tatsuo Kobayashi, Osamu Seto, Yuya Yamaguchi  PTEP 2014 (2014) 10, 103C01  2014/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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, single inflation scenario and the double inflation scenario. In the first scenario, the axion monodromy inflation with a sufficient number of e-fold generates a larger tensor-to-scalar ratio about $0.1 - 0.15$ but also a tiny running of 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 spectral index simultaneously.
  • Tatsuo Kobayashi, Yuji Omura  2014/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hajime Otsuka  2014/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We propose the natural inflation from the heterotic string theory on "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 K\"ahler axions and one of the K\"ahler 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 WMAP, Planck and/or BICEP2 data. During the inflation, the real parts of the moduli are also stabilized by employing the nature of the "Swiss-Cheese" Calabi-Yau manifold.
  • Yuta Hamada, Tatsuo Kobayashi, Shohei Uemura  2014/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 gauge coupling constants of these models. The tree level gauge coupling is a function of compactification moduli, string scale, string coupling and winding number 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 the same order.
  • Tatsuo Kobayashi, Osamu Seto  Mod. Phys. Lett. A, Vol. 30, No. 21 (2015) 1550106  2014/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    Recent detection of $B$-mode polarization induced from tensor perturbations by the BICEP2 experiment implies 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-Plankian 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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta  2014/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Osamu Seto  Phys. Rev. D 89, 103524 (2014)  2014/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • ABE HIROYUKI, KOBAYASHI TATSUO, OKI HIROSHI, SUMITA KEIGO, TATSUTA YOSHIYUKI  日本物理学会講演概要集  69-  (1)  13  2014/03   [Not refereed] [Not invited]
  • ABE TOMOHIRO, FUJIMOTO NORIHIRO, KOBAYASHI TATSUO, MIURA TAKASHI, NISHIWAKI KENJI, SAKAMOTO MAKOTO  日本物理学会講演概要集  69-  (1)  12  2014/03   [Not refereed] [Not invited]
  • 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  2014/03   [Not refereed] [Not invited]
  • Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino  2013/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    Using Z3 asymmetric orbifolds in heterotic string theory, we construct N=1 SUSY three-generation models with the standard model gauge group SU(3)_C \times SU(2)_L \times U(1)_Y and the left-right symmetric group SU(3)_C \times SU(2)_L \times SU(2)_R \times U(1)_{B-L}. One of the models possesses a gauge flavor symmetry for the Z3 twisted matter.
  • 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  2014/03   [Not refereed] [Not invited]
  • Yuta Hamada, Tatsuo Kobayashi, Shohei Uemura  JHEP1405(2014)116  2014/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi  JCAP01(2014)024  2013/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Takeshi Araki, Hiroyuki Ishida, Hajime Ishimori, Tatsuo Kobayashi, Atsushi Ogasahara  Phys. Rev. D 88, 096002 (2013)  2013/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Meeting abstracts of the Physical Society of Japan  68-  (2)  2013/08   [Not refereed] [Not invited]
  • ABE HIROYUKI, KOBAYASHI TATSUO, OKI HIROSHI, TSUNODA KEIGO, TATSUTA YOSHIYUKI  日本物理学会講演概要集  68-  (2)  1  2013/08   [Not refereed] [Not invited]
  • Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto  Prog.Theor.Phys.Suppl.183:1-163,2010  2010/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We review pedagogically non-Abelian discrete groups, which play an important role in the particle physics. We show group-theoretical aspects for many concrete groups, such as representations, their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discussed them explicitly for $S_N$, $A_N$, $T'$, $D_N$, $Q_N$, $\Sigma(2N^2)$, $\Delta(3N^2)$, $T_7$, $\Sigma(3N^3)$ and $\Delta(6N^2)$, which have been applied for model building in the 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 about anomalies of non-Abelian discrete symmetries by using the path integral approach.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita, Yoshiyuki Tatsuta  2013/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the flavor landscape of particle physics models based on a ten-dimensional super Yang-Mills theory compactified on magnetized tori preserving four-dimensional ${\cal N}=1$ supersymmetry. Recently, we constructed a semi-realistic 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 four-dimensional ${\cal N}=1$ supersymmetry. We research systematically such possibilities for leading to MSSM-like models and study their phenomenological aspects.
  • 小林達夫  数理科学  51-  (7)  51  -56  2013/07   [Not refereed] [Not invited]
  • Kang-Sin Choi, Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Yuichiro Nakai, Hiroshi Ohki, Manabu Sakai  Eur.Phys.J.C67:273-282,2010  2009/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study 10D super Yang-Mills theory with the gauge groups $E_6$, $E_7$ and $E_8$. We consider the torus/orbifold compacfitication 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.
  • Florian Beye, Tatsuo Kobayashi, Shogo Kuwakino  2013/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 Z3 asymmetric orbifold construction. We also calculate gauge symmetry breaking patterns.
  • Takashi Hiramatsu, Minoru Eto, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi  2013/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Fujimoto Yukihiro, Miura Takashi, Sakamoto Makoto, Kobayashi Tatsuo, Nishiwaki Kenji  Meeting abstracts of the Physical Society of Japan  68-  (1)  2013/03   [Not refereed] [Not invited]
  • Meeting abstracts of the Physical Society of Japan  68-  (1)  2013/03   [Not refereed] [Not invited]
  • Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi  2013/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • ABE HIROYUKI, KOBAYASHI TATSUO, SUMITA KEIGO, TATSUTA YOSHIYUKI  日本物理学会講演概要集  68-  (1)  6  2013/03   [Not refereed] [Not invited]
  • FUJIMOTO YUKIHIRO, MIURA TAKASHI, SAKAMOTO MAKOTO, KOBAYASHI TATSUO, NISHIWAKI KENJI  日本物理学会講演概要集  68-  (1)  7  2013/03   [Not refereed] [Not invited]
  • Yukihiro Fujimoto, Tatsuo Kobayashi, Takashi Miura, Kenji Nishiwaki, Makoto Sakamoto  2013/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We propose a mechanism to obtain the generation of matter in the standard model. We start from the analysis of the $T^2/Z_N$ shifted orbifold with magnetic flux, which imposes a $Z_N$ symmetry on torus. We also consider several orbifolds such as $(T^2\times T^2)/Z_N$, $(T^2 \times T^2 \times T^2)/(Z_N \times Z_{N'})$ and $(T^2 \times T^2 \times T^2)/(Z_N \times Z_{N'} \times Z_{N"})$. On such orbifolds, we study the behavior of fermions in two different means, one is the operator formalism and the other is to analyze wave functions explicitly. For an interesting result, it is found that the number of zero-mode fermions is related to $N$ of the $Z_N$ symmetry. In other words, the generation of matter relates to the type of orbifolds. Moreover, we find that shifted orbifold models to realize three generations are, in general, severely restricted. For example, the three-generation model on the type of $M^4 \times (T^2 \times T^2)/Z_N$ 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.
  • Nana Geraldine Cabo Bizet, Tatsuo Kobayashi, Damian Kaloni Mayorga Pena, Susha L. Parameswaran, Matthias Schmitz, Ivonne Zavala  2013/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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'.
  • Minoru Eto, Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Keisuke Ohashi, Yutaka Ookouchi  2012/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yuta Hamada, Kohei Kamada, Tatsuo Kobayashi, Yutaka Ookouchi  JCAP 1304 (2013) 043  2012/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Akane Oikawa, Keigo Sumita  2012/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We present a particle physics model based on a ten-dimensional (10D) super Yang-Mills (SYM) theory compactified on magnetized tori preserving four-dimensional ${\cal N}=1$ 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.
  • Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka  Phys. Rev. D 86, 095026 (2012)  2012/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yuta Hamada, Tatsuo Kobayashi  Prog. Theor. Phys. 128 (2012), 903-923  2012/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki, Keigo Sumita  2012/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We present a four-dimensional (4D) ${\cal N}=1$ superfield description of supersymmetric Yang-Mills (SYM) theory in ten-dimensional (10D) spacetime with certain magnetic fluxes in compactified extra dimensions preserving partial ${\cal N}=1$ supersymmetry out of full ${\cal N}=4$. We derive a 4D effective action in ${\cal N}=1$ 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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Kazutoshi Ohta, Yuji Omura, Haruhiko Terao  Phys.Rev.D79:045003,2009  2008/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Hiroki Makino, Ken-ichi Okumura, Takashi Shimomura, Tsubasa Takahashi  2012/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 (\lambda/\kappa)/tan\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.
  • Tatsuo Kobayashi, Takashi Shimomura, Tsubasa Takahashi  2012/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the mass, the mixing and the coupling with $Z$ boson of the lightest Higgs boson in the next-to-minimal supersymmetric standard model. 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 that the realistic vacuum is deeper than false vacua, which result in constraints on the properties of the lightest Higgs boson.
  • Abe Hiroyuki, Oikawa Akane, Oki Hiroshi, Kobayasi Tatsuo, Sumita Keigo  Meeting abstracts of the Physical Society of Japan  67-  (1)  2012/03   [Not refereed] [Not invited]
  • Abe Hiroyuki, Oikawa Akane, Ohki Hiroshi, Kobayashi Tatsuo, Sumita Keigo, Nomoto Yuki  Meeting abstracts of the Physical Society of Japan  67-  (1)  2012/03   [Not refereed] [Not invited]
  • ABE HIROYUKI, OIKAWA AKANE, OKI HIROSHI, KOBAYASHI TATSUO, SUMITA KEIGO  日本物理学会講演概要集  67-  (1)  9  2012/03   [Not refereed] [Not invited]
  • 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  2012/03   [Not refereed] [Not invited]
  • Hajime Ishimori, Tatsuo Kobayashi  2012/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the lepton flavor models with the flavor symmetry (Z_N \times Z_N \times Z_N)\rtimes Z_3. Our models predict non-vanishing discrete values of \theta_{13} as well as \theta_{12} and \theta_{23} depending on N. For certain values, our models realize the tri-bimaximal mixing angles with \theta_{13}=0. For other values, our models provide with discrete deviation from the tri-bimaximal mixing angles.
  • Parity.  26-  (8)  22  -29  2011/08   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Susha L. Parameswaran, Saul Ramos-Sanchez, Ivonne Zavala  2011/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto  JHEP 0904:011,2009  2008/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hajime Ishimori, Tatsuo Kobayashi  2011/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Azeyanagi, Tatsuo Kobayashi, Atsushi Ogasahara, Koichi Yoshioka  2011/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tetsutaro Higaki, Tatsuo Kobayashi  Phys.Rev.D84:045021,2011  2011/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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. non-tachyonic saxions, in the non-supersymmetric 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. We also study the models with axions originating from matter-like fields. Our analysis on moduli stabilization is applicable even if there are not light axion multiplets.
  • Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Osamu Seto, Takashi Shimomura  Prog. Theor. Phys. 126 (2011), 1051-1076  2011/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study constraints to avoid deep unrealistic minima in the next-to-minimal supersymmetric standard model. We analyze a 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 the successful EWSB and therefore should be avoided. Necessary conditions to avoid these minima result in constraints of parameters. We show that a wide and significant region of the parameter space, especially large \lambda, is ruled out by our constraints.
  • Kiwoon Choi, Kwang Sik Jeong, Tatsuo Kobayashi, Ken-ichi Okumura  Phys.Rev.D75:095012,2007  2006/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 set-up for TeV scale mirage mediation which allows an extra-dimensional interpretation for the origin of supersymmetry breaking and naturally gives an weak-scale size of the Higgs B-parameter. The set-up 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 FCNC processes.
  • Tatsuo Kobayashi, Yuichiro Nakai, Manabu Sakai  JHEP 1106:039,2011  2011/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Manabu Sakai  2010/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki, Manabu Sakai  Int.J.Mod.Phys.A26:4067-4082,2011  2010/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Yuichiro Nakai, Ryo Takahashi  JHEP 1009:093,2010  2010/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 squared does not drastically change by taking ratios of gaugino masses of order one. The degeneracy of scalar masses for squarks and left-handed sleptons would be good to avoid the FCNC problem but that of right-handed slepton masses is weak. However, the overall size of right-handed slepton masses become larger when the bino becomes heavier. It is also pointed out that such region can be realized, and thus, that would be favorable to avoid the FCNC problem for soft scalar masses as well as A-terms.
  • 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  2010/08   [Not refereed] [Not invited]
  • Yoshimi Kanehata, Tatsuo Kobayashi, Yasufumi Konishi, Takashi Shimomura  Phys.Rev.D82:075018,2010  2010/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We analyze a scalar potential of the minimal supersymmetric standard model (MSSM) with neutrino mass operators along Unbounded-From-Below (UFB) and Color and/or Charged Breaking (CCB) 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.
  • Tatsuo Kobayashi, Takashi Shimomura  Phys.Rev.D82:035008,2010  2010/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kang-Sin Choi, Tatsuo Kobayashi  2010/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the MSSM in F-theory. Its group is the commutant to a structure group SU(5) x U(1)_Y 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.
  • Tatsuo Kobayashi, Hans Peter Nilles, Felix Plöger, Stuart Raby, Michael Ratz  Nucl.Phys.B768:135-156,2007  2006/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • 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  2010/03   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Ryosuke Maruyama, Masaki Murata, Hiroshi Ohki, Manabu Sakai  2010/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study 10D super Yang-Mills E8 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.
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki  2010/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $\Delta(54)$.
  • Tatsuo Kobayashi, Yuichiro Nakai, Ryo Takahashi  JHEP 1001:003,2010  2009/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 ($2\times10^{16}$ 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.
  • 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  2009/08   [Not refereed] [Not invited]
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki  Phys.Rev.D80:126006,2009  2009/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study torus/orbifold models with magnetic flux and Wilson line background. The number of zero-modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology.
  • Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Okada, Yusuke Shimizu, Morimitsu Tanimoto  JHEP 0912:054,2009  2009/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We have studied $\Delta(54)\times Z_2$ flavor model for leptons and sleptons. The tri-bimaximal mixing can be reproduced for arbitrary neutrino masses if vacuum alignments of scalar fields are guaranteed. The deviation from the tri-bimaximal mixing of leptons is predicted. The predicted upper bound for $\sin\theta_{13}$ is 0.06. The magnitude of $\sin\theta_{23}$ could be deviated from the maximal mixing considerably, but $\sin\theta_{12}$ is hardly deviated from the tri-maximal mixing. We have also studied SUSY breaking terms in the slepton sector. Three families of left-handed and right-handed slepton masses are degenerate. Even although flavor symmetry breaking effects are taken into account, our model leads to smaller values of flavor changing neutral currents than the present experimental bounds.
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki  Nucl.Phys.B820:317-333,2009  2009/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study non-abelian discrete flavor symmetries, which can appear in magnetized brane models. For example, $D_4$, $\Delta(27)$ and $\Delta(54)$ can appear and matter fields with several representations can appear. We also study the orbifold background, where non-abelian flavor symmetries are broken in a certain way.
  • Stefan Forste, Tatsuo Kobayashi, Hiroshi Ohki, Kei-jiro Takahashi  JHEP 0703:011,2007  2006/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We classify compactification lattices for supersymmetric Z2 times Z2 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.
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki  JHEP 0906:080,2009  2009/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • ISHIMORI HAJIME, KOBAYASHI TATSUO, OKADA HIROSHI, SHIMIZU YUSUKE, TANIMOTO MORIMITSU  日本物理学会講演概要集  64-  (1)  9  2009/03   [Not refereed] [Not invited]
  • ISHIMORI HAJIME, KOBAYASHI TATSUO, OMURA YUJI, TANIMOTO MORIMITSU  日本物理学会講演概要集  64-  (1)  18  2009/03   [Not refereed] [Not invited]
  • Hiroyuki Abe, Kang-Sin Choi, Tatsuo Kobayashi, Hiroshi Ohki  Nucl.Phys.B814:265-292,2009  2008/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Yuji Omura, Koichi Yoshioka  Phys.Rev.D78:115006,2008  2008/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 S3 and A4 flavor symmetries are broken down to the directions leading to the tri-bimaximal form of lepton mixing and realistic mass patterns.
  • Kobayashi Tatsuo, Okumura Ken-ichi  Butsuri  63-  (8)  603  -611  2008/08   [Not refereed] [Not invited]  
    Moduli play an important role in low-energy effective theory derived from superstring theory. Their vacuum expectation values provide strength of gauge and Yukawa couplings. Furthermore, their F-components contribute to supersymmetry breaking. Recently, Kachru, Kallosh, Linde and Trivedi prosoed a new type of moduli stabilization mechanism, where all of moduli are stabilized at certain values and the vacuum energy almost vanishes. Furthermore, supersymmetry breaking terms have been studied by Choi, et al. That leads to a unique pattern of soft supersymmetry breaking terms, that is called the mirage mediation. Here we review on the mirage mediation of supersymmetry breaking. In particular, we explain its implication on the fine-tunig problem in the Higgs sector of the minimal supersymmetric standard model.
  • KOBAYASHI TATSUO, OKUMURA KEN'ICHI  日本物理学会誌  63-  (8)  603  -611  2008/08   [Not refereed] [Not invited]
  • Hajime Ishimori, Tatsuo Kobayashi, Yuji Omura, Morimitsu Tanimoto  JHEP 0812:082,2008  2008/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Hiroshi Ohki  JHEP 0809:043,2008  2008/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study (4+2n)-dimensional N=1 super Yang-Mills theory on the orbifold background with non-vanishing magnetic flux. 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.
  • Takeshi Araki, Tatsuo Kobayashi, Jisuke Kubo, Saul Ramos-Sanchez, Michael Ratz, Patrick K. S. Vaudrevange  Nucl.Phys.B805:124-147,2008  2008/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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).
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto  Phys.Rev.D78:025007,2008  2008/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study non-perturbative 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 RR charge of lower dimensional D-brane. The scalar potentials including such terms have a quite rich structure. There are several local minima with different potential energies and a high barrier, whose height is of ${\cal O}(M_p^4)$. 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 potentials would be useful to realize the inflation and low-energy supersymmetry breaking.
  • Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yuji Omura, Ryo Takahashi, Morimitsu Tanimoto  Phys.Rev.D77:115005,2008  2008/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the supersymmetric model with $D_4 \times Z_2$ 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.
  • ISHIMORI HAJIME, KOBAYASHI TATSUO, OKI YO, OMURA YUJI, TAKAHASHI RYO, TANIMOTO MORIMITSU  日本物理学会講演概要集  63-  (1)  10  2008/02   [Not refereed] [Not invited]
  • Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yuji Omura, Ryo Takahashi, Morimitsu Tanimoto  Phys.Lett.B662:178-184,2008  2008/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We present the $D_4\times Z_2$ 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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura  JHEP0804:072,2008  2008/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study concretely several issues altogether, moduli stabilization, the dynamical supersymmetry (SUSY) breaking, the uplifting of SUSY anti-de Sitter (AdS) vacuum and the sequestering of hidden sector, in a simple supergravity model with a single extra dimension. The sequestering is achieved dynamically by a wavefunction localization in extra dimension. The expressions for the visible sector soft SUSY breaking terms as well as the hidden sector potential are shown explicitly in our model. 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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura  Phys.Rev.D77:065001,2008  2007/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kang-Sin Choi, Tatsuo Kobayashi  Nucl.Phys.B797:295-321,2008  2007/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura  JHEP 0711:044,2007  2007/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi  Phys.Rev.D76:105003,2007  2007/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study moduli stabilization and a realization of de Sitter vacua in generalized F-term uplifting scenarios of the KKLT-type anti-de Sitter vacuum, where the uplifting sector X directly couples to the light K\"ahler 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 {\it even with such mixing} are almost the same as those in the KKLT 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., $m_T/m_{3/2} = {\cal O}(a^2)$, where $a \sim 4 \pi^2$. In spite of such a large mass, the modulus F-term is suppressed not like $F^T = {\cal O}(m_{3/2}/a^2)$, but like $F^T = {\cal O}(m_{3/2}/a)$ for $\ln (M_{Pl}/m_{3/2}) \sim a$, because of an enhancement factor coming from the X-T mixing. Then we typically find a mirage-mediation pattern of gaugino masses of ${\cal O}(m_{3/2}/a)$, while the scalar masses would be generically of ${\cal O}(m_{3/2})$.
  • Hiroyuki Abe, Yeong Gyun Kim, Tatsuo Kobayashi, Yasuhiro Shimizu  JHEP0709:107,2007  2007/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Yuji Omura  Phys.Rev.D76:015002,2007  2007/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study, in a bottom-up approach, the fine-tuning problem between soft SUSY breaking parameters and the $\mu$-term for the successful electroweak symmetry breaking in the minimal supersymmetric standard model. It is shown that certain nontrivial ratios between gaugino masses, that is non-universal gaugino masses, are necessary at the GUT scale, in order for the fine-tuning to be reduced above 10 % order. In addition, when all the gaugino masses should be regarded as independent ones in their origins, a small gluino mass $M_3 \lesssim 120$ GeV and a non-vanishing $A$-term $A_t \sim O(M_3)$ associated to top squarks are also required at the GUT scale as well as the non-universality. On the other hand, when we consider some UV theory, which fixes ratios of soft SUSY breaking parameters as certain values with the overall magnitude, heavier spectra are allowed. It is favored that the gluino and wino masses are almost degenerate at the weak scale, while wider region of bino mass is favorable.
  • Takeshi Araki, Kang-Sin Choi, Tatsuo Kobayashi, Jisuke Kubo, Hiroshi Ohki  Phys.Rev.D76:066006,2007  2007/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 (GS) condition, indicating that these anomalies are canceled by the GS 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, which 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.
  • Kiwoon Choi, Do Young Kim, Ian-Woo Kim, Tatsuo Kobayashi  2003/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Pyungwon Ko, Tatsuo Kobayashi, Jae-hyeon Park, Stuart Raby  Phys.Rev.D76:035005,2007; Erratum-ibid.D76:059901,2007  2007/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • K. S. Babu, Tatsuo Kobayashi, Jisuke Kubo  Phys.Rev. D67 (2003) 075018  D67-   075018  2002/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Takeshi Chiba, Tatsuo Kobayashi, Masahide Yamaguchi, Jun'ichi Yokoyama  Phys.Rev.D75:043516,2007  2006/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $M_{\rm s}$. 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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi, Yuji Omura  Phys.Rev.D75:025019,2007  2006/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi  Phys.Rev.D74:045012,2006  2006/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $h_{1,1}, h_{2,1} \neq 1$ are identified.
  • Tatsuo Kobayashi, Yuji Omura, Haruhiko Terao  Phys.Rev. D74 (2006) 053005  2006/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 show that realistic results for the second and third families are obtained with natural initial conditions, e.g. $(V_{MNS})_{23} \sim 2/\sqrt{6}$, $m_s/m_b \sim V_{cb} \sim m_{\mu}/m_\tau$ and $m_c/m_t \sim (m_s/m_b)^{3/2}$. 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 $\mu \to e \gamma$ are found to be satisfied by this dynamics. In order to suppress the electric dipole moments as well as $\mu \to e \gamma$ sufficiently, more alignment of the A-terms with some reason is required.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi  Phys.Rev.D73:046005,2006  2005/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 K\"ahler 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 non-perturbative 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.
  • Tatsuo Kobayashi, Haruhiko Terao, Akito Tsuchiya  Phys.Rev.D74:015002,2006  2006/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    It is shown that fine-tuning of the Higgs parameters stronger than a few % is required at the 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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi  Nucl.Phys.B742:187-207,2006  2005/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Carlos Munoz  JHEP 0601 (2006) 044  2005/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kiwoon Choi, Kwang Sik Jeong, Tatsuo Kobayashi, Ken-ichi Okumura  Phys.Lett.B633:355-361,2006  2005/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $m_H^2\sim m_{SUSY}^2/8\pi^2$ 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 $\mu \sim B \sim m_H$ 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.
  • Tetsutaro Higaki, Noriaki Kitazawa, Tatsuo Kobayashi, Kei-jiro Takahashi  Phys.Rev. D72 (2005) 086003  2005/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study flavor structure and the coupling selection rule in intersecting D-brane configurations. 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, and it is found that their couplings are determined by discrete abelian symmetry. Our studies on the flavor structure and the coupling selection rule show that the minimal matter content of the supersymmetric standard model would have difficulty to derive realistic Yukawa matrices from stringy 3-point couplings at the tree-level. However, extended models have a richer structure, leading to non-trivial mass matrices.
  • Pyungwon Ko, Tatsuo Kobayashi, Jae-hyeon Park  Phys.Rev.D71:095010,2005  2005/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We systematically study the possibility for realizing realistic values of lepton mass ratios and mixing angles by using only renormalizable Yukawa couplings derived from 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, $\Delta m^2_{31}/\Delta m^2_{21}$, and the lepton mixing angles can be obtained in certain cases.
  • Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao  Phys.Rev. D71 (2005) 115009  2005/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • 寺尾治彦, 小林達夫, 白野宏昌  素粒子論研究  110-  (4)  D7-D8  2005/01   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Hiroaki Shirano, Haruhiko Terao  2004/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We consider dynamical realization of the democratic type Yukawa coupling matrices as the Pendelton-Ross infrared fixed points.?Such fixed points of the Yukawa couplings become possible by introducing many Higgs fields, which are made superheavy but one massless mode. Explicitly, we consider a strongly coupled GUT based on $SU(5) \times SU(5)$, where rapid convergence to the infrared fixed point generates sufficiently large mass hierarchy for quarks and leptons. Especially, it is found that the remarkable difference between mixing angles in the quark and lepton sectors may be explained as a simple dynamical consequence. We also discuss a possible scenario leading to the 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.
  • Tatsuo Kobayashi, Stuart Raby, Ren-Jie Zhang  Nucl.Phys. B704 (2005) 3-55  2004/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    Motivated by orbifold grand unified theories, we construct a class of three-family Pati-Salam models in a Z6 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 Z2 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 S1/Z2 orbicircle. We find a horizontal 2+1 splitting in the chiral matter spectra -- 2 families of matter are localized on the Z2 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 D4 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 E6 symmetry, may give rise to interesting low energy phenomenology. We study gauge coupling unification, allowed Yukawa couplings and some of their phenomenological consequences. The E6 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.
  • Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao, Yoshihisa Yamada  Prog.Theor.Phys. 113 (2005) 413-427  2004/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We consider a mechanism for realizing the desired decoupling of 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. Vacuum instability is caused by 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 the soft mass of the singlet is at most comparable to soft masses of squarks and sleptons, which are much 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 a RG-improved effective potential.
  • Tatsuo Kobayashi, Koichi Yoshioka  JHEP 0411:024,2004  2004/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Noriaki Kitazawa, Tatsuo Kobayashi, Nobuhito Maru, Nobuchika Okada  Eur.Phys.J.C40:579-587,2005  2004/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 realistic in the 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 flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to nontrivial structures of Yukawa coupling matrices, which can be realistic.
  • Pyungwon Ko, Tatsuo Kobayashi, Jae-hyeon Park  Phys.Lett. B598 (2004) 263-272  2004/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 show realistic examples including hierarchical and democratic forms of Yukawa matrices.
  • Tatsuo Kobayashi, Haruhiko Terao  JHEP 0407 (2004) 026  2004/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Stuart Raby, Ren-Jie Zhang  Phys.Lett.B593:262-270,2004  2004/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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+SU(3)+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.
  • Tetsutaro Higaki, Tatsuo Kobayashi, Osamu Seto  JHEP 0407 (2004) 035  2004/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tetsutaro Higaki, Yoshiharu Kawamura, Tatsuo Kobayashi, Hiroaki Nakano  Phys.Lett. B582 (2004) 257-262  2003/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 K\"{a}hler 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.
  • Stefan Groot Nibbelink, Mark Hillenbach, Tatsuo Kobayashi, Martin G. A. Walter  Phys.Rev.D69:046001,2004  2003/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We investigate the structure of local anomalies of heterotic E_8 x E_8' theory on T^6/Z_4. We show that the untwisted states lead to anomalies in ten, six and four 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. Since the anomalies in all these dimensions factorize in a universal way, they can be canceled simultaneously. In addition, we show that for all U(1) factors at the four dimensional fixed points at least logarithmically divergent Fayet--Ilopoulos tadpoles are generated.
  • Tatsuo Kobayashi, Osamu Seto  Phys.Rev. D69 (2004) 023510  D-  2003/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We investigate the possibility of $D$-term inflation within the framework of type I string-inspired models. Although $D$-term inflation model has the excellent property that it is free from the so-called $\eta$- problem, two serious problems appear when we embed $D$-term inflation in string theory, the magnitude of FI term and the rolling motion of the dilation. 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 non-perturbative 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.
  • Tetsutaro Higaki, Yoshiharu Kawamura, Tatsuo Kobayashi, Hiroaki Nakano  Phys.Rev. D69 (2004) 086004  2003/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study the $D$-term contribution for anomalous U(1) symmetries in type I string models and derive general formula for the $D$-term contribution, assuming that the dominant source of SUSY breaking is given by $F$-terms of the dilaton, (overall) moduli or twisted moduli fields. On the basis of the formula, we also point out that there are several different features from the case in heterotic string models. The differences originate from the different forms of K\"ahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models.
  • Kiwoon Choi, Do Young Kim, Ian-Woo Kim, Tatsuo Kobayashi  Eur.Phys.J. C35 (2004) 267-275  2003/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS_5 which generate the hierarchical Yukawa couplings by dynamically localizing the bulk matter fields in 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 can be naturally suppressed, thereby avoiding the SUSY flavor problem. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework.
  • Tatsuo Kobayashi, Oleg Lebedev  Phys.Lett. B565 (2003) 193-200  2003/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tetsutaro Higaki, Tatsuo Kobayashi  Phys.Rev.D68:046006,2003  2003/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We consider the model with the dilaton and twisted moduli fields, which is inspired by type I string models. Stabilization of their vacuum expectation values is studied. We find the stabilization of the twisted moduli field has different aspects from the dilaton stabilization.
  • Tatsuo Kobayashi, Jisuke Kubo, Haruhiko Terao  Phys.Lett. B568 (2003) 83-91  2003/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    The exact discrete flavor symmetry, $S_3$ in the hadronic sector and $S_3 \times Z_2$ 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.
  • Tatsuo Kobayashi, Oleg Lebedev  Phys.Lett. B566 (2003) 164-170  2003/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    Realistic heterotic string models require the presence of the Wilson lines. We study the effect of continuous Wilson lines on the heterotic Yukawa couplings and find that the presence of continuous Wilson lines affects the magnitude of the twisted Yukawa couplings resulting in their stronger hierarchy.
  • Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao, Koichi Yoshioka  Prog.Theor.Phys. 110 (2003) 247-267  2002/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 this phenomenologically dangerous effects by separating the flavor-breaking sector from supersymmetry-breaking one. The separation can be achieved in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor symmetries give sizable generation-dependent masses of scalars. The gaugino mass effects are generic and not suppressed even if the dominant $D$-term contribution is suppressed. We also analyze the constraints on the flavor symmetry sector from these flavor-violating corrections.
  • Tatsuo Kobayashi, Hiroaki Nakano, Tatsuya Noguchi, Haruhiko Terao  JHEP 0302:022,2003  2002/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Hiroyuki Abe, Tetsutaro Higaki, Tatsuo Kobayashi  Prog.Theor.Phys. 109 (2003) 809-830  2002/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Jisuke Kubo, Myriam Mondragon, George Zoupanos  Nucl.Phys. B550 (1999) 99-122  1998/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 renormalizaion group technique to derive the matching condition between the effective, renormalizable and original, unrenormalizable theories. We investigate whether the assumption on 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.
  • Hiroyuki Abe, Tatsuo Kobayashi, Nobuhito Maru, Koichi Yoshioka  Phys.Rev. D67 (2003) 045019  2002/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Hiroaki Nakano, Tatsuya Noguchi, Haruhiko Terao  Phys.Rev. D66 (2002) 095011  2002/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We discuss issues in a scenario that hierarchical Yukawa couplings are generated through strong dynamics of superconformal field theories (SCFTs). Independently of mediation mechanism of supersymmetry breaking, infrared convergence property of SCFTs can provide an interesting solution to 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 SM gaugino masses. We discuss under what conditions the degeneracy of sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then study explicitly 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) \times U(1) model, each right-handed lepton is still an SU(5)-singlet, whereas the bino mass M_1 is determined by two independent gaugino masses of SU(5) \times U(1). These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate how further improvement can be obtained in the SCFT approach.
  • Tatsuo Kobayashi, Nobuhito Maru, Koichi Yoshioka  Eur. Phys. J.  C29-   277  2001/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    In this letter, we discuss a four-dimensional model with modulus fields which are responsible for supersymmetry breaking. Given non-trivial moduli dependence of the action, the model is found to give a proper description of higher-dimensional supersymmetry breaking. We explicitly calculate 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.
  • Tatsuo Kobayashi, Haruhiko Terao  Prog.Theor.Phys. 107 (2002) 785-792  107-  (4)  785  -792  2001/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $\ell$. It is shown that the finite result is obtained as long as $\ell \gg R\Lambda$ for the compactification radius $R$.
  • Kobayashi Tatsuo  Soryushiron Kenkyu  103-  (6)  F43  -F46  2001/09   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Haruhiko Terao  Phys.Rev. D64 (2001) 075003  2001/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We study soft SUSY breaking parameters in the Nelson-Strassler type of models: SUSY standard models coupled with SCFTs. In this type of models, soft SUSY breaking parameters including sfermion masses can be suppressed around the decoupling scale of SCFTs. We clarify the condition to derive exponential suppression of sfermion masses within the framework of pure SCFTs. 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 SM 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 Electro-Weak scale by a singlet field coupled with the SCFT.
  • Tatsuo Kobayashi, Hiroaki Nakano, Haruhiko Terao  Phys.Rev. D65 (2002) 015006  2001/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We propose a new type of supersymmetric models coupled to superconformal field theories (SCFT's), 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 SM sector and the SC sector. Interestingly, this hierarchy is inversely transferred to the Yukawa couplings in the SM sector. In this type of models, 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.
  • Tatsuo Kobayashi  Phys.Lett. B506 (2001) 187-192  506-  (1/2)  187  -192  2000/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $O((\alpha T/S)^2)$.
  • Manuel Drees, Yeong Gyun Kim, Tatsuo Kobayashi, Mihoko M. Nojiri  Phys.Rev.D63:115009,2001  2000/11   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We compare predictions for the spin-independent contribution to the neutralino-proton scattering cross section $\sig$ 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 $\sig$, 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 $a_\mu$ 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 $\sig$ but $a_\mu$ below the currently foreseen sensitivity. A string-inspired model with non-universal scalar spectrum at the GUT scale falls between these two cases.
  • Masako Bando, Tatsuo Kobayashi, Tatsuya Noguchi, Koichi Yoshioka  Phys.Rev. D63 (2001) 113017  2000/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 necessary conditions to obtain hierarchies between generations on the fixed point. These conditions restrict how the fields in the models can extend to higher dimension. Several specific mechanisms to realize the conditions are presented. We also take account of generation mixing effects and find a scenario where the mixing angles become small at low energy even with large initial values at high-energy scale. A toy model is shown to lead realistic quark mass matrices.
  • Tatsuo Kobayashi, Koichi Yoshioka  Phys.Rev. D62 (2000) 115003  2000/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 soft masses. We also discuss possible realizations of this scenario and the characteristic sparticle spectrum in the models.
  • Tatsuo Kobayashi, Koichi Yoshioka  Phys.Rev.Lett. 85 (2000) 5527-5530  2000/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Koichi Yoshioka  Phys.Lett.B486:223-227,2000  486-  (1/2)  223  -227  2000/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Haruhiko Terao  Phys.Lett. B489 (2000) 233-242  2000/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KOBAYASHI TATSUO  Soryushiron Kenkyu  101-  (2)  B25  -B26  2000/05   [Not refereed] [Not invited]
  • Marcela Carena, Katri Huitu, Tatsuo Kobayashi  Nucl.Phys.B592:164-182,2001  2000/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Shaaban Khalil, Tatsuo Kobayashi, Oscar Vives  Nucl.Phys. B580 (2000) 275-288  2000/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Masako Bando, Tatsuo Kobayashi, Tatsuya Noguchi, Koichi Yoshioka  Phys.Lett. B480 (2000) 187-192  2000/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Shaaban Khalil, Tatsuo Kobayashi  Phys.Lett.B460:341-347,1999  B460-  341  -347  1999/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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, $\epsilon'/\epsilon \sim 10^{-3}$.
  • Katri Huitu, Yoshiharu Kawamura, Tatsuo Kobayashi, Kai Puolamaki  Phys.Lett. B468 (1999) 111-117  1999/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Katri Huitu, Tatsuo Kobayashi  Phys.Lett. B470 (1999) 90-94  470-  (1/4)  90  -94  1999/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • S. M. Harun-or-Rashid, Tatsuo Kobayashi, Hitoshi Shimabukuro  Phys.Lett. B466 (1999) 95-99  1999/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Jisuke Kubo, Hitoshi Shimabukuro  Nucl.Phys. B580 (2000) 3-28  1999/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Katri Huitu, Yoshiharu Kawamura, Tatsuo Kobayashi, Kai Puolamaki  Phys.Rev. D61 (2000) 035001  1999/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 to 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.
  • Masud Chaichian, Tatsuo Kobayashi  Phys.Lett. B481 (2000) 26-32  481-  (1)  26  -32  1999/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Shaaban Khalil, Tatsuo Kobayashi, Antonio Masiero  Phys.Rev. D60 (1999) 075003  1999/04   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KUBO JISUKE, KOBAYASHI TATSUO, SHIMABUKURO HITOSHI  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  1998/12   [Not refereed] [Not invited]
  • Andreas Karch, Tatsuo Kobayashi, Jisuke Kubo, George Zoupanos  Phys.Lett. B441 (1998) 235-242  1998/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Masud Chaichian, Tatsuo Kobayashi  Phys.Lett. B442 (1998) 192-198  1998/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KOBAYASHI TATSUO  Soryushiron Kenkyu  97-  (4)  D31  -D33  1998/07   [Not refereed] [Not invited]
  • Yoshiharu Kawamura, Tatsuo Kobayashi, Manabu Watanabe  Int.J.Mod.Phys. A15 (2000) 81-104  1998/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi, Hitoshi Shimabukuro  Phys.Lett.B436:108-116,1998  1998/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Masud Chaichian, Wen-Feng Chen, Tatsuo Kobayashi  Phys.Lett. B432 (1998) 120-127  1998/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Jisuke Kubo, George Zoupanos  Phys.Lett.B427:291-299,1998  1998/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Jisuke Kubo, Myriam Mondragon, George Zoupanos  Nucl.Phys. B511 (1998) 45-68  1997/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 the non-universality of the SSB terms and requiring that the lightest superparticle particleis neutral, we constrain the parameter space of the SSB sector in each model.
  • KUBO HARUSUKE, KOBAYASHI TATSUO, SHIMABUKURO HITOSHI  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  1997/12   [Not refereed] [Not invited]
  • Shaaban Khalil, Tatsuo Kobayashi  Nucl.Phys.B526:99-114,1998  1997/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $b \to s \gamma$. We show three regions in the whole parameter space which lead to successful electroweak breaking and allow small SUSY corrections to the bottom mass. For these three regions we investigate the $b \to s \gamma$ decay and mass spectra.
  • Yoshiharu Kawamura, Tatsuo Kobayashi Jisuke Kubo  Phys.Lett. B432 (1998) 108-113  1997/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi, Manabu Watanabe  Phys.Lett. B419 (1998) 157-166  419-  (1/4)  157  -166  1997/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Naruhiko Aizawa, Tatsuo Kobayashi, Haru-Tada Sato  Int.J.Mod.Phys. A12 (1997) 5867-5883  1997/06   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KAWAMURA YOSHIHARU, KOBAYASHI TATSUO  素粒子論研究  95-  (1)  A60-A61  1997/04   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Hiroaki Nakano  Nucl.Phys. B496 (1997) 103-131  1996/12   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    ``Anomalous'' U(1) gauge symmetry with 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 the 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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi, Jisuke Kubo  Phys.Lett. B405 (1997) 64-70  1997/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Shaaban Khalil, Tatsuo Kobayashi  Nucl.Phys.B502:37-58,1997  1997/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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 $b \to s \gamma$ 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 $b \to s \gamma$ decay decreasing its branching ratio. We obtain an upper bound for the gravitino mass from the cosmological constraint.
  • Yoshiharu Kawamura, Tatsuo Kobayashi, Tohru Komatsu  Phys.Lett. B400 (1997) 284-294  400-  (3/4)  284  -294  1996/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Zhi-zhong Xing  Mod.Phys.Lett. A12 (1997) 561-572  1996/09   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi  Phys.Rev. D56 (1997) 3844-3859  56-  (7)  3844  -3859  1996/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi  Nucl.Phys. B481 (1996) 539-576  1996/07   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Yoshio Yamagishi  Phys.Lett. B381 (1996) 169-176  1996/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Yoshiharu Kawamura, Tatsuo Kobayashi  Phys.Lett.B375:141-148,1996; ERRATUM-ibid.B388:867,1996  1996/01   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KOBAYASHI TATSUO, YAMAGISHI YOSHIO  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  1995/12   [Not refereed] [Not invited]
  • Kobayashi Tatsuo, Yamagishi Yoshio  Abstracts of the meeting of the Physical Society of Japan. Sectional meeting  1995-  (1)  1995/09   [Not refereed] [Not invited]
  • KOBAYASHI TATSUO, YAMAGISHI YOSHIO  日本物理学会講演概要集(分科会)  1995-  (Autumn Pt 1)  14  1995/09   [Not refereed] [Not invited]
  • Kobayashi Tatsuo, Suematsu Daijiro, Yamada Kiyonori, Yamagishi Yoshio  Abstracts of the meeting of the Physical Society of Japan. Annual meeting  50-  (1)  1995/03   [Not refereed] [Not invited]
  • KOBAYASHI TATSUO, SUEMATSU DAIJIRO, YAMADA KIYONORI, YAMAGISHI YOSHIO  日本物理学会講演概要集(年会)  50th-  (1)  17  1995/03   [Not refereed] [Not invited]
  • Kobayashi Tatsuo  Soryushiron Kenkyu  90-  (3)  C81  -C85  1994/12   [Not refereed] [Not invited]
  • 小林達夫  素粒子論研究  90-  (2)  B51  1994/11   [Not refereed] [Not invited]
  • Tatsuo Kobayashi  Mod.Phys.Lett.A8:3741-3748,1993  8-  (39)  3741  -3748  1993/08   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • KOBAYASHI TATSUO, KONMURA MASAHIKO, SUEMATSU DAIJIRO, YAMADA KIYONORI, YAMAGISHI YOSHIO  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  1994/11   [Not refereed] [Not invited]
  • Tatsuo Kobayashi  Z.Phys. C60 (1993) 101-110  60-  (1)  101  -109  1993/03   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kobayashi Tatsuo  Soryushiron Kenkyu  89-  (4)  D92  -D94  1994/07   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Tsuneo Uematsu  Phys.Lett. B306 (1993) 27-33  1993/02   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Tatsuo Kobayashi, Tsuneo Uematsu  Z.Phys. C58 (1993) 559-566  1992/10   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    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.
  • Kobayashi T  1992-  (1)  1992/09   [Not refereed] [Not invited]
  • 小林達夫  日本物理学会講演概要集(分科会)  1992-  (Autumn Pt 1)  2  1992/09   [Not refereed] [Not invited]
  • Tatsuo Kobayashi, Tsuneo Uematsu  Z.Phys. C56 (1992) 193-200  56-  (2)  193  -199  1992/05   [Not refereed] [Not invited]  Institution technical report and pre-print, etc.  
    We investigate non-commutative differential calculus on the supersymmetric version of quantum space where the non-commuting super-coordinates consist of bosonic as well as fermionic (Grassmann) coordinates. Multi-parametric quantum deformation of the general linear supergroup, $GL_q(m|n)$, is studied and the explicit form for the ${\hat R}$-matrix, which is the solution of the Yang-Baxter equation, is presented. We derive the quantum-matrix commutation relation of $GL_q(m|n)$ and the quantum superdeterminant. We apply these results for the $GL_q(m|n)$ to the deformed phase-space of supercoordinates and their momenta, from which we construct the ${\hat R}$-matrix of q-deformed orthosymplectic group $OSp_q(2n|2m)$ and calculate its ${\hat R}$-matrix. Some detailed argument for quantum super-Clifford algebras and the explict expression of the ${\hat R}$-matrix will be presented for the case of $OSp_q(2|2)$.
  • Soryushiron Kenkyu  85-  (4)  D3  -D5  1992/07   [Not refereed] [Not invited]
  • KOBAYASHI TATSUO  素粒子論研究  85-  (4)  D3-D5  1992/07   [Not refereed] [Not invited]
  • Phys. Lett.  212-  (3)  339  -342  1988   [Not refereed] [Not invited]
  • Phys. Lett.  218-  (2)  169  -175  1989   [Not refereed] [Not invited]
  • Prog. Theor. Phys.  82-  (1)  171  -182  1989   [Not refereed] [Not invited]
  • Phys. Lett.  227-  (3/4)  381  -386  1989   [Not refereed] [Not invited]
  • "ZN Orbifold Models", (jointly worked)
    Nucl. Phys.  B341-  611  -640  1990   [Not refereed] [Not invited]
  • "Yukawa Coupling Condition of ZN Orbifold Models", (jointly worked)
    Phys. Lett.  B245-  441  -446  1990   [Not refereed] [Not invited]
  • "Analyses on the Wilson Lines of ZN Orbifold Models", (jointly worked)
    Phys. Lett.  B257-  56  -62  1991   [Not refereed] [Not invited]
  • Phys. Lett.  262-  (4)  425  -431  1991   [Not refereed] [Not invited]
  • "Correspondence of Z4×Z4 Orbifold Model and 26 Model"
    Suppl. Prog. Theor. Phys.  110-  277  -290  1992   [Not refereed] [Not invited]
  • Prog. Theor. Phys  88-  (2)  431  -442  1992   [Not refereed] [Not invited]
  • Z. Phys.  58-  (4)  559  -565  1993   [Not refereed] [Not invited]
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  • Phys. Lett.  329-  (1)  27  -32  1994   [Not refereed] [Not invited]
  • "Minimal String Unification and Constraint on Hidden Sector", (jointly worked)
    Nucl. Phys.  B434-  210  -230  1995   [Not refereed] [Not invited]
  • Int. J. Mod. Phys.  10-  (10)  1393  -1411  1995   [Not refereed] [Not invited]
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  • Tatsuo KOBAYASHI, Masahiko KONMURA, Daijiro SUEMATSU, Kiyonori YAMADA, Yoshio YAMAGISHI  Prog. Theor. Phys.  94-  (3)  417  -433  1995   [Not refereed] [Not invited]
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  • Int. J. Mod. Phys.  11-  (5)  903  -920  1996   [Not refereed] [Not invited]
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  • Nucl. Phys.  B481-  539  -576  1996   [Not refereed] [Not invited]
  • Mod. Phys. Lett.  12-  (8)  561  -571  1997   [Not refereed] [Not invited]
  • Int. J. Mod. Phys.  12-  (32)  5867  -5883  1997   [Not refereed] [Not invited]
  • "Anomalous U(1) Symmetry in Orbifold String Models"(jointly worked)
    Nucl. Phys.  B496-  103  -131  1997   [Not refereed] [Not invited]
  • Phys. Lett.  405-  (1/2)  64  -70  1997   [Not refereed] [Not invited]
  • "Phenomenological Implications of Moduli-dominant SUSY Breaking"(jointly worked)
    Nucl. Phys.  B502-  37  -58  1997   [Not refereed] [Not invited]
  • Int. J. Mod. Phys.  13-  (13)  2201  -2215  1998   [Not refereed] [Not invited]
  • "Constraints on Finite Soft Supersymmetry-Breaking Terms"(jointly worked)
    Nucl. Phys.  B511-  45  -68  1998   [Not refereed] [Not invited]
  • "Yukawa Unification in Moduli-dominant SUSY Breaking"(jointly worked)
    Nucl. Phys.  B526-  99  -114  1998   [Not refereed] [Not invited]
  • Phys. Lett.  427-  (3/4)  291  -299  1998   [Not refereed] [Not invited]
  • Phys. Lett.  432-  (1/2)  108  -113  1998   [Not refereed] [Not invited]
  • Phys. Lett.  432-  (1/2)  120  -127  1998   [Not refereed] [Not invited]
  • Phya. Lett.  436-  (1/2)  108  -116  1998   [Not refereed] [Not invited]
  • Phys. Lett.  441-  (1/4)  235  -242  1998   [Not refereed] [Not invited]
  • Phys. Lett.  442-  (1/4)  192  -198  1998   [Not refereed] [Not invited]
  • "Running of Soft Parameters in Extra Space-Time Dimensions"(jointly worked)
    Nucl. Phys.  B550-  99  -122  1999   [Not refereed] [Not invited]
  • "CP violation in supersymmetric model with non-degenerate A-terms"(jointly worked)
    Phys. Rev.  D60-  075003  1999   [Not refereed] [Not invited]
  • Phys. Lett.  466-  (2/4)  95  -99  1999   [Not refereed] [Not invited]
  • Phys. Lett.  468-  (1/2)  111  -117  1999   [Not refereed] [Not invited]
  • "Bottom-up Approach to B-parameter in Minimal Supersymmetric Standard Model"(jointly worked)
    Int. J. Mod. Phys.  A15-  81  -104  2000   [Not refereed] [Not invited]
  • "Phenomenological Constraints on SUSY SU(5) GUTs with Non-universal Gaugino Masses"(jointly worked)
    Phys. Rev.  D61-  035001  2000   [Not refereed] [Not invited]
  • "Electroweak symmetry breaking and s-spectrum in M-theory"(jointly worked)
    Nucl. Phys.  B580-  3  -28  2000   [Not refereed] [Not invited]
  • Phys. Lett.  480-  (1/2)  187  -192  2000   [Not refereed] [Not invited]
  • "EDM-free supersymmetric CP violation with non-universal soft terms"(jointly worked)
    Nucl. Phys.  B580-  275  -288  2000   [Not refereed] [Not invited]
  • "Infrared alignment of SUSY flavor structures"(jointly worked)
    Phys. Rev.  D62-  115003  2000   [Not refereed] [Not invited]
  • Phys. Lett.  489-  (1/2)  233  -242  2000   [Not refereed] [Not invited]
  • "RG-invariant Sum Rule in a Generalization of Anomaly-Mediated SUSY Breaking Models"(jointly worked)
    Nucl. Phys.  B592-  164  -182  2000   [Not refereed] [Not invited]
  • Phys. Rev. Lett.  85-  (26, Pt.1)  5527  -5530  2000   [Not refereed] [Not invited]
  • Phys. Rev.  D63-  113017  2001   [Not refereed] [Not invited]
  • Phys. Rev.  D63-  115009  2001   [Not refereed] [Not invited]
  • Phys. Lett.  506-  (3/4)  323  -330  2001   [Not refereed] [Not invited]
  • Sfermion masses in Nelson-Strassler-Type models : SUSY standard models coupled with SCFTs(??)
    Phys. Rev.  D64-  075003  2001   [Not refereed] [Not invited]
  • Phys. Rev.  D65-   015006  2002   [Not refereed] [Not invited]
  • Phys. Rev.  D66-   095011  2002   [Not refereed] [Not invited]
  • Phys. Rev.  D67-   045019  2003   [Not refereed] [Not invited]
  • Yukawa Hierarchy Transfer Based on Superconformal Dynamics and Geometrical Realization in String Models
    JHEP  0302-   022  2003   [Not refereed] [Not invited]
  • Prog. Theor. Phys.  109-  (5)  809  -830  2003   [Not refereed] [Not invited]
  • Prog. Theor. Phys.  110-  (2)  247  -267  2003   [Not refereed] [Not invited]
  • Phys. Lett.  568-  (1/2)  83  -91  2003   [Not refereed] [Not invited]
  • Phys. Lett.  566-  (1/2)  164  -170  2003   [Not refereed] [Not invited]
  • Phys. Rev.  D68-   046006  2003   [Not refereed] [Not invited]
  • Phys. Lett.  565-  (1/4)  193  -200  2003   [Not refereed] [Not invited]
  • Localication of Heterotic Anomalies on Various Hyper Surfaces of T^6/Z_4
    Phys. Rev.  D-   [Not refereed] [Not invited]

Research Grants & Projects

  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2008 -2011 
    Author : Tatsuo KOBAYASHI
     
    京都大学We have studied four-dimensional low-energy effective field theory, derived from superstring theory, in particular heterotic string theory on the orbifolds and magnetized/intersecting brane models. We have studied Abelian and non-Abelian discrete symmetries, which appear in these string models. Also we have studied their anomalies and found that the universal relations among certain anomalies. Furthermore, by explicit string computations we have shown stringy coupling selection rules, which seem to be difficult to understand from the symmetries of low-energy effective field theories.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2005 -2007 
    Author : Tatsuo KOBAYASHI
     
    京都大学The purpose of this research is to clarify which flavor structures can be derived from superstring theory and to study their phenomenological implications.Recently, several discrete non-Abelian flavor symmetries were proposed to derive realistic mass matrices for quarks and leptons. However, their origins are not clear in 4D field theories. In 2006, we clarified that geometrical structure of compact space can provide their origins in superstring theories and typical flavor symmetries, which can appear from heterotic orbifold models, are D4 and Delta(54). In 2007, using these results, we studied which types of quark/lepton mass matrices can be realized from D4 flavor symmetries. Furthermore, when we consider supersymmetric theories, flavor symmetries constrain not only fermion mass matrices, but also mass matrices of their superpartners, i.e. supersymmetry breaking terms. We also studied specific patterns of supersymmetric breaking terms, which are predicted from the above D4 flavor symmetries.In addition, we computed higher order couplings, i.e. their moduli-dependence. We also studied moduli stabilization, and supersymmetry breaking and their phenomenological implications.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2002 -2003 
    Author : Tatsuo KOBAYASHI
     
    京都大学Understanding the origin of fermion masses and mixing angles is one of important issues in particle physics. Within the framework of supersymmetric models, a mechanism to lead to realistic Yukawa matrices, in general, affects sfermion masses as well as the so-called A-terms. There are stringent experimental bounds on degeneracies of these SUSY breaking terms through FCNC processes. Taking into account these points, we have studied several types of flavor mechanisms.One type of flavor mechanisms which we have studied is supersymmetric standard models coupled with superconformal sectors, which have superconformal fixed points. In this type of models, superconformal dynamics generates large anomalous dimensions leading to hierarchically suppressed Yukawa couplings and at the same time controls sfermion masses so as to make them degenerate. Also we have studied flavor mechanism with 5D AdS background, which leads to the same result as the superconformal approach.We have also studied the model, which has S_3 symmetry as a flavor symmetry. Such symmetry has been studied in the literature, but it is broken at high energy. However, what is new in our model is that we extend the Higgs sector and impose the S_3 symmetry to the Higgs sector, too. The S_3 symmetry is broken around the electroweak scale. Such symmetry play a role in controlling SUSY breaking terms, so as to be consistent with experimental bounds on FCNC processes.Furthermore, we have also calculated Yukawa couplings in heterotic orbifold models including several moduli, e.g. continuous Wilson line moduli. One of our important results is that only the imaginary part of Kahler moduli contributes the physical CP phase in the Yukawa sector, while the other moduli, e.g. continuous and discrete Wilson lines do not contribute.
  • Supersymmetry Breaking and Superstring Phenomenology

Educational Activities

Teaching Experience

  • Special Lecture of Cosmosciences 1
    開講年度 : 2017
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 素粒子、高エネルギー物理学、物理学
  • Special Lecture of Cosmosciences 2
    開講年度 : 2017
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 素粒子、高エネルギー物理学、物理学
  • The World of Science and Technology
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 現代物理学入門
  • The World of Science and Technology
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : アインシュタイン、相対性理論、光速、同時性、ローレンツ変換、ローレンツ収縮、時間の遅れ、双子のパラドックス、質量とエネルギーの等価性、重力、等価原理、膨張宇宙
  • Theory of Fields
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 相対論的量子力学、Dirac 方程式、場の理論、量子電磁気学
  • Relativity
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 相対性理論、重力、宇宙論、ブラックホール
  • Mathematical Methods of Physics I
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 常微分方程式、ベクトル解析
  • Special Lecture on Quantum Mechanics
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 相対論的量子力学、Dirac 方程式、場の理論、量子電磁気学
  • Special Lectures for Modern Physics
    開講年度 : 2017
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 素粒子、高エネルギー物理学、物理学


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