顔写真

ヤマグチ マサヒロ
山口 昌弘
Masahiro Yamaguchi
所属
大学院理学研究科 物理学専攻 量子基礎物理学講座(素粒子・宇宙理論分野)
職名
教授(指定)
学位
  • 理学博士(東京大学)

  • 理学修士(東京大学)

委員歴 6

  • 高エネルギー委員会 委員

    2013年10月 ~ 2015年9月

  • 高エネルギー委員会 委員

    2013年10月 ~ 2015年9月

  • 物理学会 領域代表(素粒子論)

    2011年10月 ~ 2012年3月

  • 物理学会 領域代表(素粒子論)

    2011年10月 ~ 2012年3月

  • 素粒子論グループ 素粒子論委員会委員・幹事

    2007年4月 ~

  • 素粒子論グループ 素粒子論委員会委員・幹事

    2007年4月 ~

︎全件表示 ︎最初の5件までを表示

所属学協会 1

  • 日本物理学会

研究キーワード 2

  • 宇宙論

  • 素粒子理論

研究分野 1

  • 自然科学一般 / 素粒子、原子核、宇宙線、宇宙物理にする理論 /

論文 84

  1. Higgs Mixing in the NMSSM and Light Higgsinos 査読有り

    K.S. Jeong, Y. Shoji, M. Yamaguchi

    JHEP 1411 148 2014年11月1日

    DOI: 10.1007/JHEP11(2014)148  

  2. Higgs mixing and diphoton rate enhancement in NMSSM models 査読有り

    K. Choi, S.H. Im, K.S. Jeong, M. Yamaguchi

    JHEP 1302 090 2013年2月

  3. Light Higgsino in Heavy Gravitino Scenario with Successful Electroweak Symmetry Breaking 査読有り

    J.S. Jeong, M. Shimosuka, M. Yamaguchi

    JHEP (1209) 050 2012年9月

  4. Singlet-doublet Higgs mixing and its implications on the Higgs mass in PQ-NMSSM 査読有り

    K.S. Jeong, Y. Shoji, M. Yamaguchi

    JHEP 1209 007 2012年9月

  5. Peccei-Quinn invariant extension of the NMSSM 査読有り

    K.S. Jeong, Y. Shoji, M. Yamaguchi

    JHEP (1204) 022 2012年4月

  6. SuperTopcolor 査読有り

    H. Fukushima, R. Kitano, M. Yamaguchi

    JHEP 1101 111 2011年

  7. Axion model in gauge-mediated supersymmetry breaking and a solution to mu/Bmu problem 査読有り

    K.S. Jeong, M. Yamaguchi

    JHEP 1107 124 2011年

  8. Mixed Mediation of Supersymmetry Breaking with Anomalous U(1) Gauge Symmetry 査読有り

    K. Choi, K.S. Jeong, K. Okumura, M. Yamaguchi

    JHEP 1106 049 2011年

  9. Sparticle masses in deflected mirage mediation 査読有り

    K. Choi, K.S. Jeong, S. Nakamura, K. Okumura, M. Yamaguchi

    JHEP 0904 107 2009年4月

  10. Bs mixing phase and lepton flavor violation in supersymmetric SU(5) 査読有り

    Jae-hyeon Park, Masahiro Yamaguchi

    PHYSICS LETTERS B 670 (4-5) 356-362 2009年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2008.11.023  

    ISSN:0370-2693

    eISSN:1873-2445

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    We inspect consequences of the latest B-s mixing phase measurements on lepton flavor violation in a supersymmetric SU(5) theory. The O(1) phase, preferring a non-vanishing squark mixing, generically implies tau -> (e + mu)gamma and mu -> e gamma. Depending on the gaugino and the scalar mass parameters as well as tan beta, the rates turn out to be detectable or even already excessive, if the RR mass insertion of down-type squarks is nonzero. We find that it becomes easy to reconcile B-s mixing phase with lepton flavor violation given: gaugino to scalar squared mass ratio around 1/12, both LL and RR insertions with decent sizes, and low tan beta. (C) 2008 Elsevier B.V. All rights reserved.

  11. Sflavor mixing map viewed from a high scale in supersymmetric SU(5) 査読有り

    P. Ko, J.H. Park, M. Yamaguchi

    JHEP 0811 051 2008年11月17日

  12. Axionic mirage mediation 査読有り

    Shuntaro Nakamura, Ken-ichi Okumura, Masahiro Yamaguchi

    PHYSICAL REVIEW D 77 (11) 115027 2008年6月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevD.77.115027  

    ISSN:2470-0010

    eISSN:2470-0029

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    Although mirage mediation is one of the most plausible mediation mechanisms of supersymmetry breaking, it suffers from two crucial problems. One is the mu/B mu problem, and the second is the cosmological one. The former stems from the fact that the B parameter tends to be comparable with the gravitino mass, which is 2 orders of magnitude larger than the other soft masses. The latter problem is caused by the decay of the modulus whose branching ratio into the gravitino pair is sizable. In this paper, we propose a model of mirage mediation, in which Peccei-Quinn symmetry is incorporated. In this axionic mirage mediation, it is shown that the Peccei-Quinn symmetry breaking scale is dynamically determined around 10(10) GeV to 10(12) GeV due to the supersymmetry breaking effects, and the mu problem can be solved naturally. Furthermore, in our model, the lightest supersymmetric particle (LSP) is the axino, that is, the superpartner of the axion. The overabundance of the LSPs due to decays of the modulus/gravitino, which is the most serious cosmological difficulty in the mirage mediation, can be avoided if the axino is sufficiently light. The next-LSPs (NLSPs) produced by the gravitino decay eventually decay into the axino LSPs, yielding the dominant component of the axinos remaining today. It is shown that the axino with a mass of O(100) MeV is naturally realized, which can constitute the dark matter of the Universe, with a free-streaming length of the order of 0.1 Mpc. The saxion, the real scalar component of the axion supermultiplet, can also be cosmologically harmless due to the dilution of the modulus decay. The lifetime of the NLSP is relatively long, but much shorter than 1 sec, when the big-bang nucleosynthesis commences. The decay of the NLSP would provide intriguing collider signatures.

  13. A note on Polonyi problem 査読有り

    Shuntaro Nakamura, Masahiro Yamaguchi

    PHYSICS LETTERS B 655 (3-4) 167-171 2007年11月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2007.09.001  

    ISSN:0370-2693

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    We reinvestigate the cosmological Polonyi problem in the case where the Polonyi mass is O(10) TeV or larger. Such a large supersymmetry breaking scale implies that the Polonyi field should be sequestered from the Standard Model sector. Since the Polonyi field does not have a coupling to the gauge multiplets at tree level, in order to obtain sufficiently high reheating temperature compatible with the standard big-bang nucleosynthesis the Polonyi mass well exceeds 100-1000 TeV, depending on the decay channels. Moreover, we find that the branching ratio of the Polonyi field into neutralinos is of order unity, and thus the resulting neutralino LSPs, if stable, overclose the Universe even for the case of the wino-like LSP. Our explicit computation given here exhibits a very serious cosmological difficulty for models where supersymmetry breaking is caused by the Polonyi-type field. (C) 2007 Elsevier B.V. All rights reserved.

  14. Four-dimensional effective M theory on a singular G(2) manifold 査読有り

    Lara B. Anderson, Adam B. Barrett, Andre Lukas, Masahiro Yamaguchi

    PHYSICAL REVIEW D 74 (8) 086008 2006年10月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.74.086008  

    ISSN:1550-7998

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    We reduce M theory on a G(2) orbifold with codimension four singularities, taking explicitly into account the additional gauge fields at the singularities. As a starting point, we use 11-dimensional supergravity coupled to seven-dimensional super-Yang-Mills theory, as derived in a previous paper. The resulting four-dimensional theory has N=1 supersymmetry with non-Abelian N=4 gauge theory subsectors. We present explicit formulas for the Kahler potential, gauge-kinetic function and superpotential. In the four-dimensional theory, blowing up of the orbifold is described by a Higgs effect induced by continuation along D-flat directions. Using this interpretation, we show that our results are consistent with the corresponding ones obtained for smooth G(2) spaces. In addition, we consider the effects of switching on flux and Wilson lines on singular loci of the G(2) space, and we discuss the relation to N=4 super-Yang-Mills theory.

  15. Gravitino production from heavy moduli decay and cosmological moduli problem revived 査読有り

    Shuntaro Nakamura, Masahiro Yamaguchi

    PHYSICS LETTERS B 638 (5-6) 389-395 2006年7月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2006.05.078  

    ISSN:0370-2693

    eISSN:1873-2445

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    The cosmological moduli problem for relatively heavy moduli fields is reinvestigated. For this purpose we examine the decay of a modulus field at a quantitative level. The modulus dominantly decays into gauge bosons and gauginos, provided that the couplings among them are not suppressed in the gauge kinetic function. Remarkably the modulus decay into a gravitino pair is unsuppressed generically, with a typical branching ratio of order 0.01. Such a large gravitino yield after the modulus decay causes cosmological difficulties. The constraint from the big-bang nucleosynthesis pushes up the gravitino mass above 10(5) GeV. Furthermore to avoid the over-abundance of the stable neutralino lightest superparticles (LSPs), the gravitino must weigh more than about 10(6) GeV for the wino-like LSP, and even more for other neutralino LSPs. This poses a stringent constraint on model building of low-energy supersymmetry. (c) 2006 Elsevier B.V. All rights reserved.

  16. Gravitinos from heavy scalar decay 査読有り

    Takehiko Asaka, Shuntaro Nakamura, Masahiro Yamaguchi

    PHYSICAL REVIEW D 74 (2) 023520 2006年7月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevD.74.023520  

    ISSN:2470-0010

    eISSN:2470-0029

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    Cosmological issues of the gravitino production by the decay of a heavy scalar field X are examined, assuming that the damped coherent oscillation of the scalar once dominated the energy of the universe. The coupling of the scalar field to a gravitino pair is estimated both in spontaneous and explicit supersymmetry breaking scenarios, with the result that it is proportional to the vacuum expectation value of the scalar field in general. Cosmological constraints depend on whether the gravitino is stable or not, and we study each case separately. For the unstable gravitino with M-3/2 similar to 100 GeV-10 TeV, we obtain not only the upper bound, but also the lower bound on the reheating temperature after the X decay, in order to retain the success of the big-bang nucleosynthesis. It is also shown that it severely constrains the decay rate into the gravitino pair. For the stable gravitino, similar but less stringent bounds are obtained to escape the overclosure by the gravitinos produced at the X decay. The requirement that the free-streaming effect of such gravitinos should not suppress the cosmic structures at small scales eliminates some regions in the parameter space, but still opens a new window for the gravitino warm dark matter. Implications of these results to inflation models are discussed. In particular, it is shown that modular inflation will face serious cosmological difficulty when the gravitino is unstable, whereas it can escape the constraints for the stable gravitino. A similar argument offers a solution to the cosmological moduli problem, in which the moduli is relatively heavy while the gravitino is light.

  17. Gravitational Kaluza-Klein modes in warped superstring compactification 査読有り

    T Noguchi, M Yamaguchi, M Yamashita

    PHYSICS LETTERS B 636 (3-4) 221-226 2006年5月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2006.03.040  

    ISSN:0370-2693

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    The Kaluza-Klein (KK) modes of graviton are studied in the IIB superstring compactification where the warped geometry is realized at the Klebanov-Strassler (KS) throat. Knowledge of the metric of the KS throat enables us to determine their wave functions with good accuracy, without any further specification of the rest of Calabi-Yau space, owing to the localization of the KK modes. Mass spectrum and couplings to the four-dimensional fields are computed for some type of the KK modes, and compared to those of the well-known Randall-Sundrum model. We find that the properties of the KK modes of the two models are very different in both the masses and the couplings, and thus they are distinguishable from each other experimentally. (c) 2006 Elsevier B.V. All rights reserved.

  18. Hierarchical mass structure of fermions in warped extra dimensions 査読有り

    S Chang, CS Kim, M Yamaguchi

    PHYSICAL REVIEW D 73 (3) 033002 2006年2月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.73.033002  

    ISSN:1550-7998

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    The warped bulk standard model has been studied in the Randall-Sundrum background on S-1/Z(2)xZ '(2) interval with the bulk gauge symmetry SU(3)xSU(2)(L)xSU(2)(R)xU(1)(B-L). With the assumption of no large cancellation between the fermion flavor mixing matrices, we present a simple analytic method to determine the bulk masses of standard model fermions in the almost universal bulk Yukawa coupling model. We also predict U-e3 element of MNS matrix to be near the experimental upper bound when the neutrino masses are of Dirac type.

  19. Neutralino dark matter from heavy gravitino decay 査読有り

    K Kohri, M Yamaguchi, J Yokoyama

    PHYSICAL REVIEW D 72 (8) 083510 2005年10月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevD.72.083510  

    ISSN:2470-0010

    eISSN:2470-0029

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    We propose a new scenario of nonthermal production of neutralino cold dark matter, in which the overproduction problem of lightest supersymmetric particles (LSPs) in the standard thermal history is naturally solved. The mechanism requires a heavy modulus field which decays mainly to ordinary particles releasing large entropy to dilute gravitinos produced just after inflation and thermal relics of LSPs. Significant amount of gravitinos are also pair-produced at the decay, which subsequently decay into the neutralinos. We identify the regions of the parameter space in which the requisite abundance of the neutralino dark matter is obtained without spoiling the big-bang nucleosynthesis by injection of hadronic showers from gravitino decay. The neutralino abundance obtained in this mechanism is insensitive to the details of the superparticle mass spectrum, unlike the standard thermal abundance. We also briefly mention the testability of the scenario in future experiments.

  20. Bottom-up approach to moduli dynamics in heavy gravitino scenario: Superpotential, soft terms, and sparticle mass spectrum 査読有り

    M Endo, M Yamaguchi, K Yoshioka

    PHYSICAL REVIEW D 72 (1) 015004 2005年7月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevD.72.015004  

    ISSN:2470-0010

    eISSN:2470-0029

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    The physics of moduli fields is examined in the scenario where the gravitino is relatively heavy with mass of order 10 TeV, which is favored in view of the severe gravitino problem. The form of the moduli superpotential is shown to be determined, if one imposes a phenomenological requirement that no physical CP phase arise in gaugino masses from conformal anomaly mediation. This bottom-up approach allows only two types of superpotential, each of which can have its origins in a fundamental underlying theory such as superstring. One superpotential is the sum of an exponential and a constant, which is identical to that obtained by Kachru et al. (KKLT), and the other is the racetrack superpotential with two exponentials. The general form of soft supersymmetry-breaking masses is derived, and the pattern of the superparticle mass spectrum in the minimal supersymmetric standard model is discussed with the KKLT-type superpotential. It is shown that the moduli mediation and the anomaly mediation make comparable contributions to the soft masses. At the weak scale, the gaugino masses are rather degenerate compared to the minimal supergravity, which bring characteristic features on the superparticle masses. In particular, the lightest neutralino, which often constitutes the lightest superparticle and thus a dark matter candidate, is a considerable admixture of gauginos and Higgsinos. We also find a small mass hierarchy among the moduli, gravitino, and superpartners of the standard-model fields. Cosmological implications of the scenario are briefly described.

  21. Recent measurements of CP asymmetries of B -> phi K-0 and B -> eta ' K-S at B-factories suggest new CP violation in left-handed squark mixing 査読有り

    M Endo, S Mishima, M Yamaguchi

    PHYSICS LETTERS B 609 (1-2) 95-101 2005年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2004.12.049  

    ISSN:0370-2693

    eISSN:1873-2445

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    Recent results on the mixing-induced CP asymmetries of B --> phiK(0) and B --> eta'K-S measured at B-factories appear to indicate discrepancies from the Standard Model expectation. Explanation of this possible anomaly is given in the context of supersymmetric extension of the Standard Model. It is shown that the present data, if the average of two experiments is taken, implies additional CP violation appearing in the generation mixing of left-handed squarks rather than that of right-handed ones. This explanation is argued to disfavor many mediation mechanisms of supersymmetry breaking, including minimal supergravity, because renormalization group effects via Yukawa interaction are unlikely to generate the desired mass mixing. (C) 2004 Elsevier B.V. All rights reserved.

  22. Production and dilution of gravitinos by modulus decay 査読有り

    K Kohri, M Yamaguchi, J Yokoyama

    PHYSICAL REVIEW D 70 (4) 43522 2004年8月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.70.043522  

    ISSN:0556-2821

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    We study the cosmological consequences of generic scalar fields like moduli which decay only through gravitationally suppressed interactions. We consider a new production mechanism of gravitinos from moduli decay, which might be more effective than previously known mechanisms, and calculate the final gravitino-to-entropy ratio to compare with the constraints imposed by successful big bang nucleosynthesis (BBN) etc., taking possible hadronic decays of gravitinos into account. We find the modulus mass smaller than similar to10(4) TeV is excluded. On the other hand, inflation models with high reheating temperatures T(R,inf)similar to10(16) GeV can be compatible with BBN thanks to the late-time entropy production from the moduli decay if model parameters are appropriately chosen.

  23. Large supersymmetric contribution to CP asymmetry of B-d ->phi K-S from left-handed squark mixing 査読有り

    M Endo, M Kakizaki, M Yamaguchi

    PHYSICS LETTERS B 594 (1-2) 205-212 2004年7月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2004.05.006  

    ISSN:0370-2693

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    Supersymmetric contribution to the CP asymmetry of B-d --> phiK(S) is re-examined. It is emphasized that our analysis takes into account the recently found constraint from the mercury electric dipole moment, in addition to the well-known constraint from the branching ratio of b --> sgamma. We show that, despite these constraints, the CP asymmetry can considerably deviate from the Standard Model prediction, if the CP-odd flavor mixing comes from left-handed squarks. Alignment mechanism of sfermion masses and mixing may imprint the required flavor mixing at high energy scale. (C) 2004 Elsevier B.V. All rights reserved.

  24. Radiative CP phases in supergravity theories 査読有り

    M Endo, M Yamaguchi, K Yoshioka

    PHYSICS LETTERS B 586 (3-4) 382-389 2004年4月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2004.02.035  

    ISSN:0370-2693

    eISSN:1873-2445

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    In this Letter, we point out that possible sources of CP violation originate from radiative corrections to soft terms which are ubiquitous in supergravity theories and also in other high-energy frameworks of supersymmetry breaking. With these radiative phases of gaugino masses and scalar couplings, a complex phase of Higgs holomorphic mass parameter is generated via renormalization-group running down to low energy. It is found that its phase value is mainly controlled by wino as well as gluino, which generally receive different radiative corrections to their complex phases, even if the leading part of mass parameters follow from the universality hypothesis. The radiatively generated phases are constrained by the existing experimental bounds on electric dipole moments, and may be detectable in future measurements. They are also found to be available for the cancellation mechanism to be worked. (C) 2004 Published by Elsevier B.V.

  25. New constraint on squark flavor mixing from Hg-199 electric dipole moment 査読有り

    M Endo, M Kakizaki, M Yamaguchi

    PHYSICS LETTERS B 583 (1-2) 186-191 2004年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2003.12.075  

    ISSN:0370-2693

    eISSN:1873-2445

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    A new constraint is obtained on the CP-violating flavor mixing between the left-handed top scalar quark ((t) over tilde (L)) and charm scalar quark ((c) over tilde (L)), by considering a chargino loop contribution to chromo-electric dipole moment of strange quark, which is limited by the electric dipole moment of the Hg-199 atom. It is found that the flavor mixing should be suppressed to the level of O(0.1) for the CP phase of order unity, when tan beta is relatively large and sparticle masses lie in a few hundred GeV range. Although it is much stronger than the known constraint from the chargino loop contribution to b --> sgamma, the moderate constraint we obtain here is argued to leave room for sizable supersymmetric contribution to the CP asymmetry in B-d(0) --> phiK(S). (C) 2004 Published by Elsevier B.V.

  26. Raising sfermion masses by adding extra matter fields 査読有り

    M Endo, M Yamaguchi, A Yotsuyanagi

    PHYSICS LETTERS B 580 (3-4) 243-248 2004年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2003.11.039  

    ISSN:0370-2693

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    The renormalization group flow of soft supersymmetry breaking masses is sensitive to the field contents of the theory one considers. We point out that the addition of extra vector-like matter fields to the minimal supersymmetric standard model raises the masses of squarks and sleptons relative to those of gauginos. We discuss its phenomenological implications. Besides an obvious effect to the superparticle mass spectrum, we find that radiative corrections from heavier stop loops increase the lightest CP-even Higgs boson mass. We also discuss impact on models with no-scale boundary conditions. It turns out that, unlike the minimal case, staus can become heavier than a B-ino like neutralino, which is cosmologically favored. (C) 2003 Published by Elsevier B.V.

  27. Proton decay, fermion masses and texture from extra dimensions in SUSY GUTs 査読有り

    M. Kakizaki, M. Yamaguchi

    Int. J. Mod. Phys. A 19 1715 2004年

    DOI: 10.1142/S0217751X04018257  

  28. Electroweak symmetry breaking in supersymmetric gauge - Higgs unification models 査読有り

    K. Choi, N. Haba, K. Jeong, K. Okumura, Y. Shimizu, M. Yamaguchi

    JHEP 402 37 2004年

  29. Singular Kahler potential and heavy top quark in a democratic mass matrix model 査読有り

    M Kakizaki, M Yamaguchi

    PHYSICS LETTERS B 573 (1-4) 123-130 2003年10月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/j.physletb.2003.08.040  

    ISSN:0370-2693

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    It is pointed out that heavy top quark mass can be attributed to a singular normalization of its kinetic term, in which rescaling into canonical one yields large top Yukawa coupling. We pursue this novel possibility in a democratic mass matrix model where only the normalization of the third generation can be different from that of the other two generations. With diagonal breaking of democratic S-3 symmetry, we show that the singular normalization for the top quark is essential to reproduce observed quark masses and mixing angles. We also briefly argue other applications of this mechanism. (C) 2003 Elsevier B.V. All rights reserved.

  30. Democratic (s)fermions and lepton flavor violation 査読有り

    K Hamaguchi, M Kakizaki, M Yamaguchi

    PHYSICAL REVIEW D 68 (5) 56007 2003年9月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevD.68.056007  

    ISSN:2470-0010

    eISSN:2470-0029

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    The democratic approach to account for fermion masses and mixing is known to be successful not only in the quark sector but also in the lepton sector. Here we extend this ansatz to supersymmetric standard models, in which the Kahler potential obeys the underlying S-3 flavor symmetries. The requirement of neutrino bi-large mixing angles constrains the form of the Kahler potential for left-handed lepton multiplets. We find that right-handed sleptons can have nondegenerate masses and flavor mixing, while left-handed sleptons are argued to have universal and hence flavor-blind masses. This mass pattern is testable in future collider experiments when superparticle masses will be measured precisely. Lepton flavor violation arises in this scenario. In particular, mu-->egamma is expected to be observed in a planned future experiment if supersymmetry breaking scale is close to the weak scale.

  31. Splitting triplet and doublet in extra dimensions 査読有り

    M. Kakizaki, M. Yamaguchi

    Prog. Theor. Phys. 107 433 2002年

    DOI: 10.1143/PTP.107.433  

  32. Bottom-tau unification in SUSY SU(5) GUT and constraints from b to s gamma and muon g-2 査読有り

    S. Komine, M. Yamaguchi

    Phys. Rev. D 65 75013 2002年

  33. Anomaly-mediated supersymmetry breaking with axion 査読有り

    N. Abe, T. Moroi, M. Yamaguchi

    JHEP 201 10 2002年

  34. U(1) flavor symmetry and proton decay in supersymmetric standard model 査読有り

    M. Kakizaki, M. Yamaguchi

    JHEP 206 32 2002年

  35. Dynamical solution to supersymmetric CP problem with vanishing B parameter'' 査読有り

    M. Yamaguchi, K. Yoshioka

    Phys. Lett. B 543 189 2002年

    DOI: 10.1016/S0370-2693(02)02454-1  

  36. Phenomenology of minimal supergravity with vanishing A and B soft supersymmetry-breaking parameters'' 査読有り

    M. Endo, M. Matsumura, M. Yamaguchi

    Phys. Lett. B 544 161 2002年

    DOI: 10.1016/S0370-2693(02)02500-5  

  37. No-scale scenario with non-universal gaugino masses'' 査読有り

    S. Komine, M. Yamaguchi

    Phys. Rev. D 63 35005 2001年

    DOI: 10.1103/PhysRevD.63.035005  

  38. Recent result from E821 experiment on muon g-2 and unconstrained minimal supersymmetric standard model 査読有り

    S. Komine, T. Moroi, M. Yamaguchi

    Phys. Lett. B 506 93 2001年

    DOI: 10.1016/S0370-2693(01)00381-1  

  39. No-scale scenarios in the light of new measurement of muon anomalous magnetic moment 査読有り

    S. Komine, T. Moroi, M. Yamaguchi

    Phys. Lett. B 507 224 2001年

    DOI: 10.1016/S0370-2693(01)00452-X  

  40. Inflation with low reheat temperature and cosmological constraint on stable charged massive particles 査読有り

    A. Kudo, M. Yamaguchi

    Phys. Lett. B 516 151 2001年

    DOI: 10.1016/S0370-2693(01)00938-8  

  41. Axion model in extra dimensions with TeV scale gravity 査読有り

    S. Chang, S. Tazawa, M. Yamaguchi

    Phys. Rev. D 61 84005 2000年

  42. Pattern of neutrino oscillations in supersymmetry with bilinear R-parity violation'' 査読有り

    F. Takayama, M. Yamaguchi

    Phys. Lett. B 476 116 2000年

    DOI: 10.1016/S0370-2693(00)00104-0  

  43. Bulk standard model in the Randall-Sundrum background'' 査読有り

    S. Chang, J. Hisano, H. Nakano, N. Okada, M. Yamaguchi

    Phys. Rev. D 62 84025 2000年

  44. Low-scale anomalous U(1) and decoupling solution to supersymmetric flavor problem 査読有り

    S. Komine, Y. Yamada, M. Yamaguchi

    Phys. Lett. B 481 67 2000年

    DOI: 10.1016/S0370-2693(00)00443-3  

  45. Gravitino dark matter without R-parity 査読有り

    F. Takayama, M. Yamaguchi

    Phys. Lett. B 485 388 2000年

    DOI: 10.1016/S0370-2693(00)00726-7  

  46. Hadronic axion model in gauge-mediated supersymmetry breaking and cosmology of saxion 査読有り

    T. Asaka, M. Yamaguchi

    Phys. Rev. D 59 125003 1999年

  47. Effects of extra space-time dimensions on the Fermi constant 査読有り

    P. Nath, M. Yamaguchi

    Phys. Rev. D 60 116004 1999年

  48. Effects of Kaluza-Klein excitations on g(mu)-2 査読有り

    P. Nath, M. Yamaguchi

    Phys. Rev. D 60 116006 1999年

  49. Probing the nature of compactification with Kaluza-Klein excitations at the Large Hadron Collider 査読有り

    P. Nath, Y. Yamada, M. Yamaguchi

    Phys. Lett. B 466 100 1999年

    DOI: 10.1016/S0370-2693(99)01141-7  

  50. The formation of Cosmic structures in a light gravitino dominated universe 査読有り

    YAMAGUCHI Masahiro

    Physcical Review D 57 2089 1998年

    DOI: 10.1103/PhysRevD.57.2089  

  51. Axion cosmology with its scalar superpartner 査読有り

    M. Hashimoto, K.I. Izawa, M. Yamaguchi, T. Yanagida

    Phys. Lett. B 437 44 1998年

    DOI: 10.1016/S0370-2693(98)00887-9  

  52. Gravitino overproduction through moduli decay 査読有り

    M. Hashimoto, K.I. Izawa, M. Yamaguchi, T. Yanagida

    Prog. Theor. Phys. 100 395 1998年

    DOI: 10.1143/PTP.100.395  

  53. Late-time entropy production and relic abundances of neutralinos 査読有り

    T. Nagano, M. Yamaguchi

    Phys. Lett. B 438 267 1998年

    DOI: 10.1016/S0370-2693(98)00989-7  

  54. Relic abundance of neutralinos in heterotic string theory: Weak coupling vs. strong coupling 査読有り

    Y. Kawamura, H.P. Nilles, M. Olechowski, M. Yamaguchi

    JHEP 9806 8 1998年

  55. Hadronic axion model in gauge-mediated supersymmetry breaking 査読有り

    T. Asaka, M. Yamaguchi

    Phys. Lett. B 437 51 1998年

    DOI: 10.1016/S0370-2693(98)00890-9  

  56. Supersymmetry breakdown at a hidden wall 査読有り

    H.P. Nilles, M. Olechowski, M. Yamaguchi

    Nucl. Phys. B 530 43 1998年

  57. Exact Event Rates of Lepton Flavor Violating Processes in Supersymmefric SU(5)Model 査読有り

    YAMAGUCHI Masahiro

    Physics Letter B 391 341 1997年

    DOI: 10.1016/S0370-2693(96)01473-6  

  58. Supersymmetry Breaking and Soft Terms in M Theory 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 415 (1) 24 1997年

    DOI: 10.1016/S0370-2693(97)01212-4  

  59. Post inflationary behaviour of string moduli 査読有り

    A Lukas, A Niemeyer, M Yamaguchi

    NUCLEAR PHYSICS B 481 (1-2) 433-452 1996年12月

    出版者・発行元:ELSEVIER SCIENCE BV

    ISSN:0550-3213

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    We analyze the behaviour of moduli fields in string effective models between the end of inflation and reheating. The effective moduli potential during this era is derived for a class of simple models. We argue that this potential significantly stabilizes the modulus at its high energy minimum, if some restrictions on modular weights are met. Two mechanisms to further stabilize the moduli to their low energy minima are discussed explicitly: coinciding minima at a point of enhanced symmetry, and the smooth transition from high to low energy minimum by an effective mass term (CH2)-H-2. For both cases we present explicit examples, and C-2 is found to be O(10) at most. In addition, we show that during a smooth transition the reduction of the modulus amplitude strongly depends on the shape of the low energy potential.

  60. Particle production and gravitino abundance after inflation 査読有り

    H Fujisaki, K Kumekawa, M Yoshimura, M Yamaguchi

    PHYSICAL REVIEW D 54 (4) 2494-2503 1996年8月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.54.2494  

    ISSN:0556-2821

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    Thermal history after inflation is studied in a chaotic inflation model with supersymmetric couplings of the inflaton to matter fields. The time evolution equation is solved in a formalism that incorporates both the back reaction of particle production and the cosmological expansion. The effect of the parametric resonance gives rise to a rapid initial phase of the inflaton decay followed by a slow second stage of the decay whose rate is given by the Born approximation. Thermalization takes place immediately after the first explosive stage for a medium strength of the coupling among created particles. As an application we calculate the time evolution of the gravitino abundance that is produced by ordinary particles directly created from the inflaton decay, which typically results in a much more enhanced yield than what a naive estimate based on the Born approximation would suggest.

  61. Particle production and dissipative cosmic field 査読有り

    H Fujisaki, K Kumekawa, M Yamaguchi, M Yoshimura

    PHYSICAL REVIEW D 53 (12) 6805-6812 1996年6月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.53.6805  

    ISSN:0556-2821

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    The large amplitude oscillation of a cosmic field that may occur right after inflation and in the decay process of weakly interacting fields gives rise to violent particle production via the parametric resonance. In the large amplitude limit the problem of back reaction against the field oscillation is formulated for Yukawa-type inflaton coupling, and the energy spectrum of created particles is determined in a semiclassical approximation, assuming that interaction among created particles is weak. For a large enough amplitude the field decay is rapid, and the resulting energy spectrum is broadly distributed, implying larger production of high energy particles than what a simple estimate of the reheating temperature due to the Born formula would suggest.

  62. Lepton-flavor violation via right-handed neutrino Yukawa couplings in the supersymmetric standard model 査読有り

    J Hisano, T Moroi, K Tobe, M Yamaguchi

    PHYSICAL REVIEW D 53 (5) 2442-2459 1996年3月

    出版者・発行元:AMERICAN PHYSICAL SOC

    DOI: 10.1103/PhysRevD.53.2442  

    ISSN:0556-2821

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    Various lepton-flavor-violating (LFV) processes in the supersymmetric standard model with right-handed neutrino supermultiplets are investigated in detail. It is shown that large LFV rates are obtained when tan beta is large. In the case where the mixing matrix in the lepton sector has a similar structure as the Kobayashi-Maskawa matrix and the third-generation Yukawa coupling is as large as that of the top quark, the branching ratios can be as large as B(mu-->e gamma)similar or equal to 10(-11) and B(tau-->mu gamma)similar or equal to 10(-7), which are within the reach of future experiments. If we assume a large mixing angle solution to the atmospheric neutrino problem, the rate for the process tau-->mu gamma becomes larger. We also discuss the difference between our case and the case of the minimal SU(5) grand unified theory.

  63. Light Gravitino as Mixed Dark Matter 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 386 189 1996年

    DOI: 10.1016/0370-2693(96)00956-2  

  64. Geometric bremsstrahlung in the earlyuniverse 査読有り

    YAMAGUCHI Masahiro

    Progress of Theoretical Physics 96 113 1996年

    DOI: 10.1143/PTP.96.113  

  65. LEPTON-FLAVOR VIOLATION IN THE SUPERSYMMETRIC STANDARD MODEL WITH SEESAW-INDUCED NEUTRINO MASSES 査読有り

    J HISANO, T MOROI, K TOBE, M YAMAGUCHI, T YANAGIDA

    PHYSICS LETTERS B 357 (4) 579-587 1995年9月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/0370-2693(95)00954-J  

    ISSN:0370-2693

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    We examine the lepton-flavor violation caused by a Yukawa coupling matrix y(nu ij) for right-handed neutrinos in the supersymmetric standard model. We stress that decay rates for tau --> mu gamma and mu --> e gamma are largely enhanced in a parameter region where left-right mixing terms in the slepton mass matrix are substantially large. Especially, these decay rates may reach the range to be accessible to near future experiments even if the SO(10)-like boundary condition on y(vij) is used. We also discuss how the rates behave if one changes the ansatz on the Yukawa coupling matrix for the right-handed neutrinos.

  66. Precision Study of Supersymmetry at Future Linear e<SUP>+</SUP>e<SUP>-</SUP> Colliders 査読有り

    YAMAGUCHI Masahiro

    Physical Review D51 3153 1995年

    DOI: 10.1103/PhysRevD.51.3153  

  67. Low-Energy Effective Lagrangian in Unified Theories with Non-Universal Supersymmetry Breaking Terms 査読有り

    YAMAGUCHI Masahiro

    Physical Review D51 1337 1995年

    DOI: 10.1103/PhysRevD.51.1337  

  68. THE HEAVY POLONYI FIELD AS A SOLUTION OF THE POLONYI PROBLEM 査読有り

    JOICHI, I, M YAMAGUCHI

    PHYSICS LETTERS B 342 (1-4) 111-116 1995年1月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/0370-2693(94)01338-D  

    ISSN:0370-2693

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    We study properties of the Polonyi held in the renormalizable hidden sector in supergravity models. It is shown that radiative corrections induce a sizeable coupling of the Polonyi field to gravitinos as well as raise its mass to an intermediate scale. We find that it provides a solution of the Polonyi problem and show that the gravitino abundance produced by the Polonyi decay is not large. It is also pointed out that soft supersymmetry breaking terms induced by this hidden sector are very restricted.

  69. On the Solution to the Polonyi Problem with O(10 TeV) Graviton Mass in Supergravity 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 342 105 1995年

    DOI: 10.1016/0370-2693(94)01337-C  

  70. PROBING THE SYMMETRY-BREAKING PATTERN USING SFERMION MASSES 査読有り

    Y KAWAMURA, H MURAYAMA, M YAMAGUCHI

    PHYSICS LETTERS B 324 (1) 52-58 1994年3月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/0370-2693(94)00107-3  

    ISSN:0370-2693

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    We study the mass spectrum of superparticles within supersymmetric grand unified models. For gaugino masses, it is pointed out that the GUT relation in the SU(5) model is applicable to a more general case where a grand-unified gauge group breaks down to the standard model gauge group by several steps. We also show that the mass spectrum of squarks and sleptons carries the information on the breaking pattern of the gauge symmetry. It is demonstrated in some SO(10) models how the scalar mass spectrum distinguishes various SO(10) breaking patterns from each other.

  71. Light Scalar Top Quark in the Minimal Supersymmetric Grand Unified Theory 査読有り

    YAMAGUCHI Masahiro

    Physical Review Letters 72 3009 1994年

    DOI: 10.1103/PhysRevLett.72.3009  

  72. COSMOLOGICAL CONSTRAINTS ON THE LIGHT STABLE GRAVITINO 査読有り

    T MOROI, H MURAYAMA, M YAMAGUCHI

    PHYSICS LETTERS B 303 (3-4) 289-294 1993年4月

    出版者・発行元:ELSEVIER SCIENCE BV

    DOI: 10.1016/0370-2693(93)91434-O  

    ISSN:0370-2693

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    Cosmological constraints when the gravitino is the lightest superparticle are studied. From the condition that the relic gravitinos should not overclose the universe, the upper bound on the reheating temperature of the universe is found to be 10(2)-10(10) GeV in a range of gravitino mass 10(-5)-10 GeV. Furthermore, if the decay of the next-to-the-lightest superparticle produces sizable high energy photons, constraints from the light element (D, He-3, He-4) photodestruction exclude a range of the gravitino mass.

  73. PHENOMENOLOGICAL ASPECTS OF SUPERSYMMETRIC STANDARD MODELS WITHOUT GRAND UNIFICATION 査読有り

    S MIZUTA, D NG, M YAMAGUCHI

    PHYSICS LETTERS B 300 (1-2) 96-103 1993年2月

    出版者・発行元:ELSEVIER SCIENCE BV

    ISSN:0370-2693

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    When the GUT relation on gaugino masses is relaxed, the mass and composition of the lightest neutralino are different from those in the GUT case. We discuss its phenomenological implications on the relic abundance of the neutralinos and on superparticle searches. In particular, we focus on the case where the neutral component of winos dominates the lightest neutralino. It turns out that the wino-LSP is not a candidate for the dark matter.

  74. Is Axino Dark Matter Possible in Supergravity? 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 276 (1-2) 1993年

  75. Bottom Qnark Mass Predictions in Non-Supersymmetric SU(5) Unification 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 277 (1-2) 1993年

  76. Coannihilation Effects and Relic Abundance of Higgsino Dominant LSPs 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 298 (3-4) 289 1993年

  77. Vanishing Squark and Slepton Masses in Supergravity 査読有り

    YAMAGUCHI Masahiro

    Physical Review D 45 (1) 1992年

    DOI: 10.1103/PhysRevD.45.328  

  78. Mass Degeneracy of Squarks and Sleptons in Supergravity 査読有り

    YAMAGUCHI Masahiro

    Progress of Theoretical Physics 86 (3) 1992年

    DOI: 10.1143/PTP.86.717  

  79. Renormalization-Group Analysis on the Higgs Mass in the Softly-Broken Supersymmetric Standard Model 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 262 (1) 1991年

    DOI: 10.1016/0370-2693(91)90642-4  

  80. Upper Bound of the Lightest Higgs Boson Mass in the Minimal Supersymmetric Standard Model 査読有り

    YAMAGUCHI Masahiro

    Progress of Theoretical Physics 85 (1) 1991年

    DOI: 10.1143/PTP.85.1  

  81. P and Q Operator Analysis for Two-Matrix Model 査読有り

    YAMAGUCHI Masahiro

    Physics Letters B 250 (1-2) 1990年

  82. Gauge Deformations of Conformal Filed Theories and Zamolodchikou's C-Function 査読有り

    YAMAGUCHI Masahiro

    International Journal of Modern Physics A 5 (22) 1990年

    DOI: 10.1142/S0217751X90001781  

  83. Ambiguities and BRST Anomalies in 4D Heterofic String Theories 査読有り

    YAMAGUCHI Masahiro

    International Journal of Modern Physics A 5 (3) 1990年

    DOI: 10.1142/S0217751X90000234  

  84. Boson-Fermion Mass Spliffings in Four-Dimensional Heterofic string Models with Anomalous U(1) Gauge Groups 査読有り

    YAMAGUCHI Masahiro

    Nuclear Physics B 327 (3) 1989年

︎全件表示 ︎最初の5件までを表示

MISC 4

  1. 大型ハドロン衝突器時代の弦理論

    M.ダイン(山口

    パリティ 2008 (8) 46-55 2008年8月

    出版者・発行元:丸善

    ISSN:0911-4815

  2. ヒッグス粒子はどこにあるか?

    山口昌弘

    数理科学 45 (11) 47-52 2007年11月

    出版者・発行元:サイエンス社

  3. Prospects of physics beyond the standard model: Supersymmetry

    Masahiro Yamaguchi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 (11) 111012 2007年11月

    出版者・発行元:PHYSICAL SOC JAPAN

    DOI: 10.1143/JPSJ.76.111012  

    ISSN:0031-9015

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    Despite the success of the standard model of particle physics, there are reasons to expect new physics beyond it. Supersymmetric extension is a promising possibility, which solves the fine-tuning problem inherent to the origin of the electroweak scale in the standard model. It also provides a promising candidate for dark matter. The verification of low-energy supersymmetry in forthcoming experiments will lead us to a new paradigm of particle physics, in particular, it may open up the road to the unification of forces.

  4. アクシオンは存在するか

    山口昌弘

    数理科学 44 (12) 55-58 2006年12月

    出版者・発行元:サイエンス社

講演・口頭発表等 10

  1. Mirage Mediation of Supersymmetry Breaking: Phenomenology and Cosmology 国際会議

    TeV Particle Astrophysics 2008年9月24日

  2. Axionic mirage mediation 国際会議

    Japan-France joint workshop on Cosmology of the Early Universe 2008年5月14日

  3. Axionic Mirage Mediation 国際会議

    Pheno08 2008年4月28日

  4. Gravitational Kaluza-Klein modes in warped string compactification 国際会議

    International Conference of High Energy Physics in Cairo 2006年1月14日

  5. Flavor physics in SUSY 国際会議

    Higgs&SUSY conference 2005年11月23日

  6. Extra Dimensions at Terascale 国際会議

    Japansese-American Frontiers of Science Symposium 2005年11月10日

  7. b to s transitions in SUSY: left-handed vs. right-handed 国際会議

    3rd International conference on flavor physics 2005年10月2日

  8. 宇宙論との接点(シンポジュウム・国際リニアコライダー計画の進展)

    日本物理学会 2005年9月12日

  9. Phenonemonogy and cosmology of heavy gravitino scenario

    素粒子物理学の進展 2005年6月21日

  10. Phenomenology and cosmology of heavy gravitino scenario 国際会議

    Particle, Strings and Cosmology (PASCOS) 2005年5月30日

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社会貢献活動 2

  1. 出前授業(鶴岡南高)

    2009年9月29日 ~

  2. 出前授業(仙台二高)

    2008年12月4日 ~

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    素粒子から宇宙まで:物理学研究の最前線

その他 1

  1. 余剰次元をもつ模型に基づく素粒子物理と宇宙論

    詳細を見る 詳細を閉じる

    余剰次元をもつ模型に基づく素粒子物理と宇宙論の研究