Updated on 2022/04/12

TOBE, Kazuhiro

Organization
Graduate School of Science Associate professor
School of Science

### Degree 1

1. 博士（理学） （ 1997.3   東北大学 ）

### Research Interests 7

1. Physics beyond the standard model

2. lepton flavor violation

3. Flavor Physics

4. Higgs physics

5. Little Higgs model

6. Supersymmetric model

7. Grand unified theory

### Research Areas 1

1. Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics  / Elementary Particle/Atomic Nucleus/Cosmic Ray/Space Physics

### Current Research Project and SDGs 4

1. フレーバー物理におけるアノマリーから探る新物理の理論研究

2. Lepton flavor violation in physics beyond the standard model

3. LHC Phenomenology in the physics beyond the standard model

4. ミュー粒子異常磁気能率のアノマリーを説明する新物理の理論的研究

### Research History 9

1. Nagoya University   Graduate School of Science Division of Particle and Astrophysical Sciences Fundamental Theoretical Physics   Associate professor

2008.4

2. Nagoya University   Division of Theoretical Studies   Associate professor

2010.4

3. Assistant professor

2007.4 - 2008.3

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Country：Japan

4. Michigan State University, Research assistant professor

2004.9 - 2007.3

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Country：United States

5. Univ. of Michigan, Postdoc researcher

2002.10 - 2004.8

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Country：United States

6. UC Davis, Postdoc researcher

2001.10 - 2002.9

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Country：United States

7. CERN, Postdoc researcher

1999.10 - 2001.9

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Country：Switzerland

8. Ohio State University, Postdoc researcher

1997.9 - 1999.9

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Country：United States

9. 東京大学　学振研究員

1996.4 - 1997.8

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Country：Japan

### Education 3

1. Tohoku University   Graduate School, Division of Natural Science   Department of Physics

1994.4 - 1997.3

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Country： Japan

2. Tohoku University   Graduate School, Division of Natural Science   Department of Physics

1992.4 - 1994.3

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Country： Japan

3. Tohoku University   Faculty of Science   Department of Physics

1988.4 - 1992.3

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Country： Japan

### Professional Memberships 1

1. The Physical Society of Japan

### Committee Memberships 3

1. 日本物理学会素粒子論領域運営委員会   委員

2012.4 - 2013.3

2. 素粒子論委員会   委員

2010.4 - 2012.3

3. 基研共同利用委員会   委員

2009.1 - 2010.12

### Papers 18

1. Syuhei Iguro, Kazuhiro Tobe

NUCLEAR PHYSICS B   Vol. 925   page： 560 - 606   2017.12

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV

Motivated by an anomaly in R(D-(*())) = BR((B) over bar -&gt; D-(*())tau(-)(nu) over bar)/BR((B) over bar -&gt; D-(*)l(-)(nu) over bar) reported by BaBar, Belle and LHCb, we study R(D-(*())) in a general two Higgs doublet model (2HDM). Although it has been suggested that it is difficult for the 2HDM to explain the current world average for R(D-(*())), it would be important to clarify how large deviations from the standard model predictions for R(D-(*())) are possible in the 2HDM. We investigate possible corrections to R(D-(*())) in the 2HDM by taking into account various flavor physics constraints (such as B-c(-) -&gt; tau(-)(nu) over bar, b -&gt; s gamma, b -&gt; sl(+)l(-), Delta m(Bd,s), B-s -&gt; mu(+)mu(-) and tau(+)tau(-), and B- -&gt; tau(-)(nu) over bar), and find that it would be possible (impossible) to accommodate the 1 sigma region suggested by the Belle's result when we adopt a constraint BR(B-c(-) -&gt; tau(-)(nu) over bar) &lt;= 30 % (BR(B-c(-) -&gt; tau(-)(nu) over bar) &lt;= 10 %). We also study productions and decays of heavy neutral and charged Higgs bosons at the Large Hadron Collider (LHC) experiment and discuss the constraints and implications at the LHC. We show that in addition to well-studied production modes bg -&gt; tH(-) and gg -&gt; H/A, exotic productions of heavy Higgs bosons such as cg -&gt; bH(+), t + H/A and c (b) over bar -&gt; H+ would be significantly large, and the search for their exotic decay modes such as H/A -&gt; t (c) over bar + c (t) over bar, mu(+/-)tau(-/+) and H+ -&gt; c (b) over bar as well as H/A -&gt; tau(+)tau(-) and H+ -&gt; tau(+)nu would be important to probe the interesting parameter regions for R(D-(*())). (C) 2017 Published by Elsevier B.V.

2. Tobe K.

Proceedings of Science   Vol. 2017-January   2017

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Language：Japanese   Publisher：Proceedings of Science

Motivated by an event excess in Higgs decay h → μτ reported by the CMS experiment, we consider a general two Higgs doublet model (2HDM) which predicts the flavor violating phenomena beyond the standard model. Within the framework of the 2HDM, we show the scenario where the μ - τ flavor violation can explain the anomaly of the muon anomalous magnetic moment as well as the CMS event excess in h→μτ. We discuss τ → μγ, the Michel parameters and lepton flavor non-universality in the t decays τ → lνν (l = e;μ) as interesting predictions in this scenario.

3. Kazuhiro Tobe

JHEP 1610 (2016) 114   Vol. 2016 ( 10 ) page： 114   2016.10

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Language：Japanese   Publishing type：Research paper (scientific journal)

4. Yuji Omura, Eibun Senaha, Kazuhiro Tobe

PHYSICAL REVIEW D   Vol. 94 ( 5 ) page： 055019   2016.9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC

Motivated by the recent CMS excess in a flavor violating Higgs decay h -&gt; mu tau as well as the anomaly of muon anomalous magnetic moment (muon g - 2), we consider a scenario where both the excess in h -&gt; mu tau and the anomaly of muon g - 2 are explained by the mu - tau flavor violation in a general two Higgs doublet model. We study various processes involving mu and tau, and then discuss the typical predictions and constraints in this scenario. Especially, we find that the prediction of tau -&gt; mu gamma can be within the reach of the Belle II experiment. We also show that the lepton nonuniversality between tau -&gt; mu nu(nu) over bar and tau -&gt; e nu(nu) over bar can be sizable, and hence the analysis of the current Belle data and the future experimental improvement would have an impact on this model. Besides, processes such as, tau -&gt; mu l(+)l(-) (l = e, mu), tau -&gt; mu eta, mu -&gt; mu gamma, mu -&gt; 3e and the muon electric dipole moment can be accessible, depending on the unknown Yukawa couplings. On the other hand, the processes like tau -&gt; e gamma and tau -&gt; el(+)l(-)(l = e, mu) could not be sizable to observe because of the current strong constraints on the e - mu and e - tau flavor violations. Then we also conclude that contrary to the h -&gt; mu tau decay mode, the lepton flavor violating Higgs boson decay modes h -&gt; e mu and h -&gt; e tau are strongly suppressed, and hence it will be difficult to observe these modes at the LHC experiment.

5. Yuji Omura, Kazuhiro Tobe, Koji Tsumura

PHYSICAL REVIEW D   Vol. 92 ( 5 ) page： 055015   2015.9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC

We investigate diboson signals in the standard model (SM) with an extended Higgs sector, motivated by the excesses in the diboson channels at the LHC. We begin with the unitarity sum rules of the weak gauge boson scattering assuming the Higgs sector is extended. According to the sum rules, we discuss the Higgs interpretations of the diboson signals and the consistency with the ATLAS diboson anomaly and other experimental constraints. As a concrete example, we propose a two-Higgs-doublet model where the Yukawa coupling of an extra CP-even scalar with up-type quark is relatively large. The diboson (WW and ZZ) signals can be explained by 2 TeV CP-even Higgs boson, while the partners, the CP-odd and the charged Higgs bosons in the extra doublet, are severely constrained by both the LHC direct search and the indirect search via flavor observables. Especially, in order to avoid the diboson resonance search in the Vh channel, further extensions of the model are required. The diboson excess is correlated with the SM Higgs signals in our framework, so that the precise measurement of the SM Higgs boson is also important to test the Higgs interpretation.

6. Yuji Omura, Eibun Senaha, Kazuhiro Tobe

JHEP   Vol. 2015 ( 5 ) page： 028   2015.5

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Language：Japanese   Publishing type：Research paper (scientific journal)

7. Tobe K.

Proceedings of Science   Vol. 25-29-May-2015   2015

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Language：Japanese   Publisher：Proceedings of Science

In a general two Higgs double model, flavor-changing phenomena mediated by neutral Higgs bosons are predicted. We find the μ - τ flavor-violating Higgs interactions in a general Higgs doublet model can explain the excess event in a Higgs decay h → μτ observed by the CMS collaboration as well as the anomaly of the muon anomalous magnetic moment, simultaneously. We also discuss that the predicition of τ → μγ in the scenario can be within the reach of the future B-factory.

8. Harigaya Keisuke, Igari Takafumi, Nojiri Mihoko M., Takeuchi Michihisa, Tobe Kazuhiro

JOURNAL OF HIGH ENERGY PHYSICS   Vol. 2014 ( 3 )   2014.3

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Language：Japanese   Publisher：Journal of High Energy Physics

In this paper, we consider phenomenology of a model with an Lμ - Lτ gauge symmetry. Since the muon couples to the Lμ - Lτ gauge boson (called Z00 boson), its contribution to the muon anomalous magnetic moment (muon g-2) can account for the discrepancy between the standard model prediction and the experimental measurements. On the other hand, the Z00 boson does not interact with the electron and quarks, and hence there are no strong constraints from collider experiments even if the Z00 boson mass is of the order of the electroweak scale. We show an allowed region of a parameter space in the Lμ - Lτ symmetric model, taking into account consistency with the electroweak precision measurements as well as the muon g-2. We study the Large Hadron Collider (LHC) phenomenology, and show that the current and future data would probe the interesting parameter space for this model. Open Access, © 2014 The Authors.

9. Tobe K.

Proceedings of Science   Vol. 2013-December   2013

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Language：Japanese   Publisher：Proceedings of Science

An anomaly of the muon anomalous magnetic moment (muon g-2) has been reported. The discrepancies between the Standard Model (SM) prediction and the measured value are about 3-4 s. If this anomaly is due to new physics beyond the SM, we expect new particles and interactions related with the muon sector. In this talk, we consider a model with an Lµ - Lt gauge symmetry. Since the muon couples to the Lµ - Lt gauge boson (called Z" boson), its contribution to the muon g-2 can account for the discrepancy. On the other hand, the Z" boson does not interact with the electron nor quarks, and hence there are no strong constraints from collider experiments even if the Z" boson mass is of the order of the electroweak scale. We show an allowed region of a parameter space in the model, taking into account consistency with the electroweak precision measurements as well as the muon g-2. We study the Large Hadron Collider (LHC) phenomenology, and show that the current and future data would probe the interesting parameter space for this model.

10. Kanemitsu Shunichi, Tobe Kazuhiro

PHYSICAL REVIEW D   Vol. 86 ( 9 )   2012.11

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Language：Japanese   Publisher：Physical Review D - Particles, Fields, Gravitation and Cosmology

About 3σ deviation from the standard model prediction of muon anomalous magnetic moment (muon g-2) has been reported. We consider new physics beyond the standard model which has new Yukawa interactions with muons. We compute new contributions to muon g-2 and corrections to electroweak observables, and show the consistent region of parameter space. We find that in a simple model where the chirality flip of a muon occurs only in the external muon line in one-loop muon g-2 diagrams, it is necessary to introduce the relatively large new Yukawa coupling and the electroweak scale new particles. On the other hand, in a model where the chirality flip can occur in the internal fermion line of one loop muon g-2 diagrams, we can obtain favorable g-2 contributions without large Yukawa coupling, and they are consistent with the precision electroweak observables. Finally, we discuss effects of new particles for muon g-2 on the Higgs boson decay h→γγ and direct productions of these particles at the LHC experiment. © 2012 American Physical Society.

11. Analysis of Higgs Boson Mass Limit from LEP Experiment in General Minimal Supersymmetric Standard Model, and the Possibility of the Light Higgs Boson Invited

Kazuhiro Tobe

Butsuri   Vol. 2009 ( 9 ) page： 691-695   2009.9

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12. Physics at a future Neutrino Factory and super-beam facility

ISS Physics Working Group(A. Bandyopadhyay et al.)(94 authors)

Rept.Prog.Phys.   Vol. 72   page： 106201   2009

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Language：English

The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21–26 June 2005) and NuFact06 (Ivine, CA, 24–30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.

13. Flavor physics and muon precision measurements at LHC era Invited

Kazuhiro Tobe

AIP Conf. Proc.   Vol. 981   page： 354-356   2008

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In this talk, I discuss important roles of precision measurements on the muon properties, such as muon lifetime, muon anomalous magnetic moment (muon g-2) and muon rare decay (µe etc.) to test the standard model of elementary particles and to search for new physics effects. I stress that even after discovering new physics effects at the LHC, these studies on muons will be complementary to the LHC physics, and therefore, the further experimental studies on muons will be very important to understand the more fundamental theory of elementary particles.

14. *Light MSSM Higgs boson scenario and its test at hadron colliders. Reviewed

A. Belyaev, Q.-H. Cao, D. Nomura, K. Tobe, C.-P. Yuan

Phys. Rev. Lett.   Vol. 100   page： 061801   2008

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Language：English   Publishing type：Research paper (scientific journal)

We show that in the Minimal Supersymmetric Standard Model, the possibility for the lightest CP-even Higgs boson to be lighter than $Z$ boson (as low as about 60 GeV) is, contrary to the usual belief, not yet excluded by LEP2 data or any other existing experimental data. The characteristic of the light Higgs boson scenario (LHS) is that the $ZZh$ coupling and the decay branching ratio ${\rm Br}(h/A\to b\bar{b})$ are simultaneously suppressed as a result of generic supersymmetric loop corrections. Consequently, the $W^\pm H^\mp h$ coupling has to be large due to the sum rule of Higgs couplings to weak gauge bosons. In addition to discussing the potential of the Tevatron and $B$-factories to test the LHS, we show that the associate neutral and charged Higgs boson production process, pp\to H^\pm h (A)$, can completely probe LHS at the CERN Large Hadron Collider. 15. *Testing the Littlest Higgs Model with T-parity at the Large Hadron Collider. Reviewed S. Matsumoto, T. Moroi, K. Tobe Phys. Rev. D78 Vol. D78 page： 055018 2008 More details Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) In the framework of the littlest Higgs model with T parity (LHT), we study the production processes of T-even (T+) and T-odd (T-) partners of the top quark at the Large Hadron Collider (LHC). We show that the signal events can be distinguished from the standard model backgrounds, and that information about mass and mixing parameters of the top partners can be measured with relatively good accuracies. With the measurements of these parameters, we show that a nontrivial test of the LHT can be performed. We also discuss a possibility to reconstruct the thermal relic density of the lightest T-odd particle AH using the LHC results and show that the scenario where AH becomes dark matter may be checked. 16. Higgs boson production and decay in a littlest Higgs model with T-parity Kazuhiro Tobe AIP Conf.Proc. Vol. 903 page： 475-478 2007 More details Authorship：Lead author Language：English We study Higgs boson production and decay in a certain class of Little Higgs models with T-parity where T-parity fermionic partners of the Standard Model (SM) fermions gain their mass through Yukawa-type interactions. We find that the Higgs boson production cross section at the CERN LHC via gluon-gluon fusion process could be significantly reduced, as compared to its SM prediction, for a relatively low new particle scale. On the other hand, the Higgs boson production cross section via weak boson fusion process is very close to the SM value. Furthermore, the Higgs boson decay branching ratio into -mode could be largely enhanced in small Higgs boson mass region in a certain case because the total decay width of Higgs boson in the Little Higgs model is smaller than that in the SM. 17. Phenomenology of littlest Higgs model with T-parity: including effects of T-odd fermions. Reviewed A. Belyaev, C.-R. Chen, K. Tobe, C.-P. Yuan Phys. Rev. D Vol. D74 page： 115020 2006 More details Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) We study the collider phenomenology of a Littlest Higgs model with T-parity. We first stress the important role of the T-odd SU(2) doublet fermions (introduced to make the model T-parity invariant) in high energy scattering processes, such as$q\bar{q}\to W_H^+ W_H^-$where$W_H^\pm$are the T-odd partners of$W\$-bosons. Because the mass of the T-odd SU(2) doublet fermions cannot be too heavy to be consistent with low energy data, they can be copiously produced at the CERN Large Hadron Collider (LHC). Therefore, we study the collider phenomenology of the model with emphasis on the contributions of the T-odd fermion to the production of the heavy T-parity partners (either bosons or fermions) of the usual particles at the LHC. The production cross sections and the decay branching ratios of the new heavy particles are classified and various experimental signatures are discussed.

18. Higgs boson production and decay in little Higgs models with T-parity. Reviewed

C.-R. Chen, K. Tobe, C.-P. Yuan

Phys. Lett. B   Vol. B640   page： 263   2006

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)

We study Higgs boson production and decay in a certain class of Little Higgs models with T-parity in which some T-parity partners of the Standard Model (SM) fermions gain their masses through Yukawa-type couplings. We find that the Higgs boson production cross section of a 120 GeV Higgs boson at the CERN LHC via gg fusion process at one-loop level could be reduced by about 45%, 35% and 20%, as compared to its SM prediction, for a relatively low new particle mass scale f = 600, 700 and 1000 GeV, respectively. On the other hand, the weak boson fusion cross section is close to the SM value. Furthermore, the Higgs boson decay branching ratio into di-photon mode can be enhanced by about 35% in small Higgs mass region in certain case, for the total decay width of Higgs boson in the Little Higgs model is always smaller than that in the SM.

### Presentations 27

1. Phenomenology of leptoquarks motivated by muon g-2 anomaly

Kazuhiro Tobe

2022.3.16

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Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)

Country：Japan

2. Flavor physics in general two Higgs doublet model Invited

Kazuhiro Tobe

The 3rd International Symposium on "Quest for the Origin of Particles and the Universe" (KMI2017)

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Event date： 2017.1

Language：English   Presentation type：Oral presentation (invited, special)

Country：Japan

3. New Physics for Muon g-2 Anomaly Invited

Kazuhiro Tobe

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Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

4. Charged Lepton Flavor Violation (CLFV), Anomalous Magnetic Moment (g-2) and Electric Dipole Moment (EDM) Invited International conference

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Event date： 2016.6

Language：English   Presentation type：Oral presentation (invited, special)

Country：United States

5. muon g-2 in general two Higgs doublet model

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Event date： 2015.6

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

6. muon g-2 in physics beyond the standard model International conference

The 10th g-2/EDM collaboration meeting

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Event date： 2015.6

Language：English   Presentation type：Oral presentation (invited, special)

Country：Japan

7. Lepton-flavor-violating Higgs decay h -> μτ and muon anomalous magnetic moment in a general two Higgs doublet model International conference

Yuji Omura, Eibun Senaha, Kazuhiro Tobe

13th COnference on Flavor Physics and CP Violation (FPCP 2015)

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Event date： 2015.5

Language：English   Presentation type：Poster presentation

Country：Japan

8. The Standard Model an Beyond International conference

Kazuhiro Tobe

CTEQ School on QCD and Electroweak phenomenology

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Event date： 2014.7

Language：English   Presentation type：Oral presentation (invited, special)

Venue：Peking University, China   Country：China

9. New physics for muon g-2 and its electroweak precision analysis International conference

Shunichi Kanemitsu, Kazuhiro Tobe

The second international workshop on LHC Era Physics (LHEP2013)

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Event date： 2013.1

Language：English   Presentation type：Oral presentation (general)

Country：China

10. B Physics in MSSM light Higgs Scenario International conference

"LHC Physics: W, Z and Beyond", 2010 Topical Program at NCTS in Taiwan

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Event date： 2010.12

Language：English   Presentation type：Oral presentation (invited, special)

11. Testing the Little Higgs Model with T-parity at the Large Hadron Collider

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Event date： 2009.4

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

12. Motivation for Lepton Flavor Violation searches

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Event date： 2008.9

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

13. Theoretical motivation for a study of lepton flavor violation

Symposium at JPS meeting

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Event date： 2008.9

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

14. Higgsが見えなくなる理論的可能性

LHCが切り拓く２１世紀の新しい素粒子物理

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Event date： 2008.3

Language：Japanese   Presentation type：Oral presentation (invited, special)

Country：Japan

15. Lepton Flavor Violation in New Physics Models International conference

Search for Baryon and Lepton Number Violation International Workshop

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Event date： 2007.9

Language：English   Presentation type：Oral presentation (invited, special)

16. Flavor physics and muon precision measurements at LHC era International conference

9th International Workshop on Neutrino Factories, Superbeams and Betabeams(NuFact 07)

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Event date： 2007.8

Language：English   Presentation type：Oral presentation (invited, special)

Country：Japan

17. Phenomenology of littlest Higgs model with T-parity

Workshop: Particle physics in the era of LHC

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Event date： 2007.7

Language：English   Presentation type：Oral presentation (invited, special)

Country：Japan

18. What can we learn from lepton flavor violation after SUSY discovery?

Conference on "Supersymmetry in 2010's"

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Event date： 2007.6

Language：English   Presentation type：Oral presentation (invited, special)

Country：Japan

19. Light MSSM Higgs boson scenario International conference

The 7-th Particle Physics Phenomenology Workshop

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Event date： 2007.6

Language：English   Presentation type：Oral presentation (invited, special)

20. The Standard Model an Beyond

Kazuhiro Tobe

CTEQ School on QCD and Electroweak phenomenology  2014.7.16

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Language：English   Presentation type：Oral presentation (invited, special)

Venue：Peking University, China

21. New Physics for Muon g-2 Anomaly Invited International conference

Kazuhiro Tobe

2016.9.5

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Language：Japanese   Presentation type：Oral presentation (invited, special)

22. New physics for muon g-2 and its electroweak precision analysis

Shunichi Kanemitsu, Kazuhiro Tobe

The second international workshop on LHC Era Physics (LHEP2013)  2013.1.11

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Language：English   Presentation type：Oral presentation (general)

23. muon g-2 in physics beyond the standard model

The 10th g-2/EDM collaboration meeting  2015.6.25

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Language：English   Presentation type：Oral presentation (invited, special)

24. muon g-2 in general two Higgs doublet model International conference

2015.6.27

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Language：Japanese   Presentation type：Oral presentation (invited, special)

25. Lepton-flavor-violating Higgs decay h -> μτ and muon anomalous magnetic moment in a general two Higgs doublet model

Yuji Omura, Eibun Senaha, Kazuhiro Tobe

13th COnference on Flavor Physics and CP Violation (FPCP 2015)  2015.5.25

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Language：English   Presentation type：Poster presentation

26. Flavor physics in general two Higgs doublet model Invited International conference

Kazuhiro Tobe

The 3rd International Symposium on "Quest for the Origin of Particles and the Universe" (KMI2017)  2017.1.5

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Language：English   Presentation type：Oral presentation (invited, special)

27. Charged Lepton Flavor Violation (CLFV), Anomalous Magnetic Moment (g-2) and Electric Dipole Moment (EDM) Invited

Kazuhiro Tobe

2nd International Conference on Charged Lepton Flavor Violation  2016.6.20

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Language：English   Presentation type：Oral presentation (invited, special)

### KAKENHI (Grants-in-Aid for Scientific Research) 8

1. Grant number：20K03947  2020.4 - 2024.3

科学研究費助成事業  基盤研究(C)

戸部 和弘

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Authorship：Principal investigator

Grant amount：\3510000 （ Direct Cost: \2700000 、 Indirect Cost：\810000 ）

B中間子の幾つかの崩壊現象で報告されている食い違い（アノマリー）を説明する新物理の候補として、レプトンとクォーク両方と結合するレプトクォークを含む理論がある。このような理論は、我々が今まで研究してきたミュー粒子異常磁気能率にも大きな効果を及ぼすものもあり、B中間子崩壊のアノマリーとミュー粒子異常磁気能率のアノマリーを複数同時に説明できるレプトクォークの理論は可能なのかを、本研究では明らかにしようとする。こうしたアノマリーを手がかりにした模型構築及びその現象論的解析から、レプトクォークを含む理論で、より統一性を持った素粒子理論を構築出来るのかを研究する。
ミュー粒子の異常磁気能率（muon g-2）は実験的に非常に精密測定されている物理量だが、その測定値が素粒子標準模型の予言値とずれていることが報告されている。またB中間子がD(*)中間子、レプトンl、ニュートリノνに崩壊する過程（B→D(*)lν）で、終状態のレプトンがτの時とそれ以外の時の崩壊率の比R(D(*))の測定値も標準模型の予言値とずれていることが報告されている。これらのずれが標準模型を超える新物理によるものだとしたら、新物理の非常に重要な手掛かりになりうる。
これらのずれを説明する候補としてレプトクォーク模型が指摘されている。レプトクォークはレプトンとクォークと同時に相互作用する新しい素粒子である。レプトクォークの中でも、ミュー粒子とトップクォークと相互作用するものは、muon g-2に１ループレベルで大きな寄与を与えうることが知られていて、そのずれを説明しうる。また一方で、このような相互作用をするレプトクォークはR(D(*))へも寄与しうるので、２つの物理量の測定値のずれをどれくらい説明できるかを明らかにすることは非常に重要である。先行研究で、両方のずれをどれだけ説明しうるかの詳しい解析は今までなされていなかったので、名古屋大学理学研究科修士２年大津颯人君の修士論文の研究でそれを詳しく解析した。
スカラータイプのレプトクォークについて解析すると、R(D(*))に大きな寄与を生成することはできるのだが、b→sνν崩壊やB中間子ー反B中間子（Bs-反Bs、Bd-反Bd）混合からの制限が非常に厳しく、R(D(*))への寄与は非常に制限されることがわかった。よってmuon g-2へは大きな寄与を生成できるが、R(D(*))へ大きな寄与を生成するのは難しいことがわかった。この制限は、ベクタータイプのレプトクォークにも有効なので、今後はその詳しい解析をしたい。
今年度はスカラーレプトクォークの模型を主に解析した。この模型はb→sνν崩壊からの制限が厳しいことが知られているが、他の様々な過程からの制限を考慮してどれだけ大きなR(D(*))のずれを出すことができるか、という詳しい解析はあまりなされていなかった。しかしこの模型で様々な過程を調べてみると、b→sνν崩壊だけでなくB中間子ー反 B中間子混合（Bs-反Bs混合、Bd-反Bd混合）からより強い制限があることが明らかになった。より興味深いベクターレプトクォーク模型は、模型のフレーバー構造など、より複雑であるが、B中間子ー反B中間子混合からの制限は、スカラーレプトクォーク模型と同様に、より重要な制限になることが期待される。今後はまずその解析を進めたい。研究の進展としてはおおむね順調である。
スカラーレプトクォークの解析で、B中間子ー反B中間子混合（Bs-反Bs混合、Bd-反Bd混合）からの制限が非常に厳しくなりうることがわかったので、まずはこれをより興味深いベクターレプトクォーク模型の解析に適用して、その制限を詳しく調べたい。この制限は、新物理として導入したレプトクォークの質量や相互作用の強さだけでなく、レプトクォークが持つフレーバー構造にも制限を与える。ベクターレプトクォーク模型の解析の大抵の先行研究では、ある特殊なフレーバー構造を仮定して、模型を解析している場合が多いようなので、このような解析からさらに模型のフレーバー構造に対する示唆が得られるのかを明らかにしたい。またそのようなフレーバー構造から予言される現象はないか、などを明らかにすることによって、標準模型自体が持つフレーバー構造の深い理解につなげたい。

2. Theoretical study of physics beyond the standard model probed from flavor physics

Grant number：16K05319  2016.4 - 2019.3

Tobe Kazuhiro

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Authorship：Principal investigator

Grant amount：\4030000 （ Direct Cost: \3100000 、 Indirect Cost：\930000 ）

We studied an muon anomalous magnetic moment (muon g-2) and B-meson decay (B→D(*)τν), where the discrepancies between the standard model predictions and the measured values (anomalies) have been reported, within a framework of a two Higgs doublet model. We found that the μーτ flavor violating interaction in the 2HDM can accommodate both an anomalous Higgs boson decay h→μτ and the anomaly of the muon g-2. We also found that it is difficult to explain the current anomaly in B→D(*)τν within the 2HDM, and the even small discrepancy in the 2HDM suggests the interesting new particle productions and decays at the LHC experiment, which can be very different from the standard model phenomena.

3. ミューオン異常磁気能率のアノマリーを説明する新物理の現象論的研究

Grant number：26104705  2014.4 - 2016.3

科学研究費助成事業  新学術領域研究(研究領域提案型)

戸部 和弘

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Authorship：Principal investigator

Grant amount：\2470000 （ Direct Cost: \1900000 、 Indirect Cost：\570000 ）

ミュー粒子異常磁気能率（muon g-2）の実験値と標準模型の予言値の食い違いを、どのような標準模型を超える新物理で説明出来るかを研究した。特に、2 Higgs doublet model（2HDM）でμーτフレーバーの破れがある模型を考えて、muon g-2のアノマリーを説明出来る可能性を詳しく研究した。μーτフレーバーの破れを考えたのは、LHC実験のCMSグループがヒッグス粒子の崩壊でh→μτの現象の兆候を報告したのに動機付けられている。標準模型では起こらないこのようなフレーバーの破れが2HDMでは自然に導入されることはよく知られているが、我々はこのようなμーτフレーバーの破れの相互作用が、muon g-2に大きな量子補正を生成することを発見し、これによって現在報告されているmuon g-2の標準模型の予言値からのズレを説明出来る可能性があることを示した。（JHEP 1505, 028 (2015)) もしこの可能性が本当である場合には、タウ粒子の崩壊τ→μγの現象が将来のSuperKEKB実験で観測される可能性があることを指摘した。さらにτ→μνν過程にも、重要な補正を生成する可能性を見つけ、この過程の精密測定及びτ→eνν過程とのレプトンユニバーサリティーの破れの精密測定の重要性を指摘した。またその他様々なμ、τ粒子の崩壊現象などへの影響も詳しく解析し、将来の実験の重要性を示した。(arXiv:1511.08880) この研究に関しては、幾つかの国内、国際会議で発表したのに加え、J-PARCのCollaboration meetingを始めとして、IPMU, 九州大, KEK, 首都大, 富山大, 島根大にセミナーに招待され、多くの理論家、実験家の人たちと議論ができて有意義であった。またミシガン大、ミシガン州立大を訪問した際に、この話題についてセミナーをし、そこでも理論家、実験家の人たちと有意義な議論ができた。
27年度が最終年度であるため、記入しない。
27年度が最終年度であるため、記入しない。

4. Studies of generation structure in new physics at terascale

Grant number：23104011  2011.4 - 2016.3

Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Hisano Junji

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Authorship：Collaborating Investigator(s) (not designated on Grant-in-Aid)

We studied flavor physics in physics beyond the standard model. Rare processes, such as lepton-flavor violating processes, and also electric dipole moments are sensitive to beyond the standard model. We showed the relations between the observables and the fundamental parameters in the models, and gave constraints on the models including supersymmetric models and extended Higgs models by combining the results of Higgs measurements and new particle searches at LHC. We also discussed the electroweak baryogeneis in the extended Higgs models. We constructed realistic grand unified models based on the LHC results, and predicted the proton decay rates. We also constructed realistic models to predict quark and lepton masses, and discussed leptogenesis in the models.

5. Symmetry Breakings and the Gauge Dynamics

Grant number：22224003  2010.4 - 2015.3

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Authorship：Coinvestigator(s)

Although the Higgs particle responsible for the origin of mass has been discovered, its dynamical origin still remains mysterious. This project showed, based on the ladder approximation and also the holographic model, that the discovered Higgs particle is consistent with the composite particle “Technidilaton”predicted by the “Walking Technicolor.
We further made the first-principle calculations of lattice QCD simulations and found that flavor 8 QCD is a candidate for the Walking Technicolor, the result later confirmed by other groups. We also discovered light flavor-singlet scalar meson for flavor-12 (later confirmed by several other groups), and also for flavor-8, the latter being a candidate for the technidilaton to be identified with the discovered Higgs particle as a composite.

6. Theoretical study on light Higgs boson scenario in the minimal supersymmetric standard model

Grant number：22540273  2010 - 2012

TOBE Kazuhiro

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Authorship：Principal investigator

Grant amount：\4160000 （ Direct Cost: \3200000 、 Indirect Cost：\960000 ）

The standard model of elementary particles (SM) has been very successful. However, before the LHC experiment started, the Higgs boson in the SM has not been discovered yet. Therefore many theoretical scenarios beyond the SM have been proposed. In this study, we consider the light Higgs boson scenario within the minimal supersymmetric standard model (MSSM) where there is a light Higgs boson whose mass is about 100 GeV. In such a light Higgs boson scenario, not only the direct search experiment such as the LEP, but also the indirect search experiments such as B factory and flavor experiments are very important. We studied the effects of the light Higgs boson on B physics, and showed that the B physics strongly constrained the light Higgs boson scenario. Furthermore, since the LHC started and discovered a SM Higgs-like new particle, the new physics scenarios beyond the SM are strongly constrained to explain the SM Higgs like new particle. We find that the light Higgs boson scenario is also strongly constrained by the current LHC results. The current LHC experiment has not been observed any new particles except the SM Higgs boson like particle. However, it has been reported that there is a discrepancy between the experimental result and the SM prediction of the muon anomalous magnetic moment (muon g-2). Therefore we studied the new physics models which can explain the muon g-2 anomaly, and showed that there are still regions which are consistent with the current experimental results. We also pointed out that the future LHC study may be important to probe the new physics models for muon g-2 anomaly.

7. LHC実験におけるリトルヒッグス模型の理論的解析

Grant number：20840021  2008.4 - 2010.3

科学研究費補助金  若手研究（スタートアップ）

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Authorship：Principal investigator

8. Theoretical studies on physics beyond the Standard Model wit flavor mixing

Grant number：18071001  2006 - 2011

HIKASA Ken-ichi

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Authorship：Coinvestigator(s)

Phenomena of flavor mixing of quarks and leptons provide important clue on the physics beyond the Standard Model. This project contains various theoretical studies on candidates of the physics beyond the Standard Model such as supersymmetry and extra dimensions, as well as related cosmology. We have obtained many new insights on each of these and contributed to the development of the field. Suggestions to present and future flavor physics experiments are given.

### Teaching Experience (On-campus) 40

1. Physics Tutorial III

2021

2. Quantum Mechanics III

2021

3. Seminar on Particle Physics 4

2021

4. Particle Physics (for G30 students)

2021

5. 物理学概論II

2021

6. Particle Physics (for G30 students)

2020

7. 物理学概論II

2020

8. 量子力学III

2019

9. 素核セミナー４

2019

10. 物理学演習III（量子）

2019

11. 物理学演習III

2018

12. 素核セミナー４

2018

13. 量子力学III

2018

14. 物理学演習II-1（解析力学II、量子力学I）

2017

15. Elementary Particle Physics

2017

16. 物理学演習III（量子力学II）

2017

17. Fundamentals of Advanced Physics I

2017

18. 素粒子

2016

19. 物理学演習 II-1 (解析力学 II、量子力学 I）

2016

20. 基礎セミナーA

2016

21. 先端物理学基礎 I

2016

22. 先端物理学基礎 I

2015

23. 素粒子

2015

24. 物理学演習II-1（解析力学II、量子力学I）

2015

25. 基礎セミナーA

2015

26. 素粒子

2014

27. 基礎セミナーA

2014

28. 先端物理学基礎I

2014

29. 素粒子

2013

30. 物理学演習III

2013

31. 基礎セミナーA

2013

32. 先端物理学基礎 I

2013

33. 素粒子

2012

34. 基礎セミナーA

2012

35. 物理学演習III

2012

36. 先端物理学基礎I

2012

37. 物理学演習II-1

2011

詳細を見る

量子力学I、解析力学IIの演習

38. 素粒子

2011

詳細を見る

素粒子の標準模型の、ニュートリノやヒッグス粒子に関するトピックスを紹介する。

39. 素核セミナー４

2011

詳細を見る

素粒子物理の教科書を輪講する。

40. 先端物理学基礎I

2011

詳細を見る

素粒子の標準模型の基礎となる場の量子論などを紹介する。

### Teaching Experience (Off-campus) 3

1. 標準模型を超える素粒子模型の間接探索について

2014.4 - 2015.3 Niigata University）

2. ヒッグス物理とnew physics

2010.4 - 2011.3 東北大学）

3. 素粒子現象論（ヒッグス粒子の物理など）

2009.4 - 2010.3 広島大学）

### Social Contribution 3

1. グローバルサイエンスキャンプ「名大　MIRAI GSC」第１ステージ講義

Role(s)：Lecturer

名古屋大学  2017.6

2. 三重県立桑名高校出前授業

2015.7

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最先端の素粒子物理に関しての講義

3. アジアサイエンスキャンプ

2009.8

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筑波で開かれたアジアサイエンスキャンプで、C.-N. Yang氏のアソシエイトを担当。