OMURA Yuji

Researcher Information

URL

https://www.phys.kindai.ac.jp/laboratory/yomura/

J-Global ID

• 201601016202666121

Research Areas

• Natural sciences / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Academic & Professional Experience

• 2022/04 - Today  Kindai UniversityFaculty of Science and Engineering准教授
• 2019/04 - 2022/03  Kindai UniversityFaculty of Science and Engineering講師
• 2016/04 - 2019/03  Nagoya University基礎理論研究センター任期付准教授
• 2015/04 - 2016/03  Nagoya University基礎理論研究センター特任助教
• 2014/04 - 2015/03  Nagoya University大学院 理学研究科特任助教
• 2012/10 - 2014/03  ミュンヘン工科大学研究員
• 2010/04 - 2012/09  Korea Institute for Advanced Study (KIAS)研究員
• 2009/04 - 2010/03  Kyoto University日本学術振興会特別研究員(PD)
• 2008/04 - 2009/03  Kyoto University日本学術振興会特別研究員(DC2)

Education

• 2004/04 - 2009/03  京都大学大学院  理学研究科
• 2000/04 - 2004/03  Kyoto University  Faculty of Science

Published Papers

• Light lepton portal dark matter meets the LHC

  Syuhei Iguro; Shohei Okawa; Yuji Omura

  Journal of High Energy Physics Springer Science and Business Media LLC 2023 (3) 2023/03 [Refereed]
   

  Abstract We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below $$ \mathcal{O}(10)\textrm{GeV} $$ and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run 2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-Z plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.
• Scrutinizing the 95–100 GeV di-tau excess in the top associated process

  Syuhei Iguro; Teppei Kitahara; Yuji Omura

  The European Physical Journal C Springer Science and Business Media LLC 82 (11) 2022/11 [Refereed]
   

  Abstract Recently, the CMS collaboration has reported a di-tau excess with a local significance of 2.6–3.1$$\sigma $$ where the invariant mass is $$m_{\tau \tau } =95$$–100 GeV. This excess can be interpreted as a light scalar boson that couples to the third generation fermions, particularly top and $$\tau $$. Based on the simplest model that can account for the CMS di-tau excess, we evaluate experimental sensitivities to the additional light resonance, using the results reported by the ATLAS collaboration. We see that a search for the top-quark associated production of the SM Higgs boson that decays into $$\tau {\bar{\tau } }$$ sets a strong model-independent limit. We also find that the CP-even scalar interpretation of the light resonance is excluded by the ATLAS results, while the CP-odd interpretation is not.
• W boson mass and muon g-2 in a lepton portal dark matter model

  Junichiro Kawamura; Shohei Okawa; Yuji Omura

  Physical Review D American Physical Society (APS) 106 (1) 2470-0010 2022/07 [Refereed]
   

  We study a lepton portal dark matter model, motivated by the deviation of the W boson mass reported by the CDF collaboration. We introduce vector-like leptons and a scalar dark matter (DM) which exclusively couples to the extra leptons and muon. The one-loop corrections induced by the new particles can shift the W boson mass. Besides, the discrepancy in the muon anomalous magnetic moment and the DM density can simultaneously be explained by this setup, if the vector-like lepton is lighter than 200 GeV and nearly degenerate with the DM particle. We also see that the constraints on such a light extra lepton from the collider experiments can be evaded due to the existence of the DM particle.
• Importance of vector leptoquark-scalar box diagrams in Pati-Salam unification with vector-like families

  Syuhei Iguro; Junichiro Kawamura; Shohei Okawa; Yuji Omura

  Journal of High Energy Physics Springer Science and Business Media LLC 2022 (7) 2022/07 [Refereed]
   

  Abstract We study lepton flavor violation (LFV) induced by one-loop box diagrams in Pati-Salam (PS) unification with vector-like families. The vector leptoquark (LQ) associated with the PS gauge symmetry breaking generally causes various LFV processes such as K_L → μe and μ → e conversion at the tree-level, thereby driving its mass scale to be higher than PeV scale. The vector-like families are introduced to suppress such tree-level LFV processes, allowing the LQ to have TeV scale mass. In this paper, we point out that there are inevitable one-loop contributions to those LFV processes from the box diagrams mediated by both one LQ and one scalar field, even if the tree-level contributions are suppressed. We consider a concrete model for demonstration, and show that the vector-like fermion masses have an upper bound for a given LQ mass when the one-loop induced processes are consistent with the experimental limits. The vector-like fermion mass should be lighter than 3 TeV for 20 TeV LQ, if a combination of the couplings does not suppress K_L → μe decay. Our findings would illustrate importance of the box diagrams involving both LQ and physical modes of symmetry breaking scalars in TeV scale vector LQ models.
• TeV-scale vector leptoquark from Pati-Salam unification with vectorlike families

  Syuhei Iguro; Junichiro Kawamura; Shohei Okawa; Yuji Omura

  Physical Review D American Physical Society (APS) 104 (7) 2470-0010 2021/10 [Refereed]
  
• Higgs flavor phenomenology in a supersymmetric left-right model with parity

  Syuhei Iguro; Junichiro Kawamura; Yuji Omura; Yoshihiro Shigekami

  Journal of High Energy Physics Springer Science and Business Media LLC 2021 (6) 2021/06 [Refereed]
   

  In this paper, we focus on the supersymmetric model with left-right (LR) symmetry, that is especially proposed in our previous work [1]. In this model, there are four Higgs doublets in order to realize the Standard Model (SM) fermion masses and the Cabibbo-Kobayashi-Maskawa matrix. The heavy Higgs doublets unavoidably have flavor changing couplings to the SM fermions and induce flavor-changing neutral currents at tree level. We study broader parameter space than the previous work with including the renormalization group corrections to the Yukawa couplings between the LR breaking scale, $$ \mathcal{O} $$ O (10¹³) GeV, and the supersymmetry breaking scales, $$ \mathcal{O} $$ O (100) TeV. The CP violating observable in K–$$ \overline{K} $$ K ¯ mixing, ϵ_K, strongly constrains the model, so that heavy Higgs mass should be heavier than $$ \mathcal{O} $$ O (100) TeV. We study the lepton flavor violating (LFV) processes setting heavy Higgs masses to be 170 TeV. The branching ratios of μ → 3e and the μ–e conversion can be larger than 10⁻¹⁶ that could be covered by the future experiments. We also study the degree of fine-tuning in the parameter region that predicts testable LFV processes.
• Light mass window of lepton portal dark matter

  Shohei Okawa; Yuji Omura

  Journal of High Energy Physics Springer Science and Business Media LLC 2021 (2) 2021/02 [Refereed]
   

  We explore a novel possibility that dark matter has a light mass below 1 GeV in a lepton portal dark matter model. There are Yukawa couplings involving dark matter, left-handed leptons and an extra scalar doublet in the model. In the light mass region, dark matter is thermally produced via its annihilation into neutrinos. In order to obtain the correct relic abundance and avoid collider bounds, a neutral scalar is required to be light while charged scalars need to be heavier than the electroweak scale. Such a mass spectrum is realized by adjusting quartic couplings in the scalar potential or introducing an extra singlet scalar. It turns out that the mass region of 10 MeV–10 GeV is almost free from experimental and observational constraints. We also point out that searches for extra neutrino flux from galactic dark matter annihilations with neutrino telescopes are the best way to test our model.
• Probing μτ flavor-violating solutions for the muon g − 2 anomaly at Belle II

  Syuhei Iguro; Yuji Omura; Michihisa Takeuchi

  Journal of High Energy Physics Springer Science and Business Media LLC 2020 (9) 1029-8479 2020/09 [Refereed]
   

  The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the μτ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the τ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensitive to the scenario in the mediator mass range of O(1–10) GeV, using the e⁺e⁻→ μ^±τ^∓X → μ^±μ^±τ^∓τ^∓ process induced by the X .
• Current status and muon g − 2 explanation of lepton portal dark matter

  Junichiro Kawamura; Shohei Okawa; Yuji Omura

  Journal of High Energy Physics Springer Science and Business Media LLC 2020 (8) 2020/08 [Refereed]
  
• Top FCNC induced by a Z′ boson

  Sungwoong Cho; P. Ko; Jungil Lee; Yuji Omura; Chaehyun Yu

  Physical Review D American Physical Society (APS) 101 (5) 2470-0010 2020/03 [Refereed]
  
• Spontaneous SUSY breaking in natural SO(10) grand unified theory

  Nobuhiro Maekawa; Yuji Omura; Yoshihiro Shigekami; Manabu Yoshida

  Physical Review D American Physical Society (APS) 100 (11) 2470-0010 2019/12 [Refereed]
  
• Testing the 2HDM explanation of the muon g – 2 anomaly at the LHC

  Syuhei Iguro; Yuji Omura; Michihisa Takeuchi

  Journal of High Energy Physics Springer Science and Business Media LLC 2019 (11) 1029-8479 2019/11 [Refereed]
   

  The discrepancy between the measured value and the Standard Model prediction for the muon anomalous magnetic moment is one of the important issues in the particle physics. In this paper, we consider a two Higgs doublet model (2HDM) where the extra Higgs doublet couples to muon and tau in lepton flavor violating (LFV) way and the one-loop correction involving the scalars largely contributes to the muon anomalous magnetic moment. The couplings should be sizable to explain the discrepancy, so that the extra Higgs bosons would dominantly decay into mu tau LFV modes, which makes the model testable at the LHC through multi-lepton signatures even though they are produced via the electroweak interaction. We discuss the current status and the future prospect for the extra Higgs searches at the LHC, and demonstrate the reconstruction of the mass spectrum using the multi-lepton events.
• The direct CP violation in a general two Higgs doublet model

  Syuhei Iguro; Yuji Omura

  Journal of High Energy Physics Springer Science and Business Media LLC 2019 (8) 2019/08 [Refereed]
  
• WIMP dark matter in the parity solution to the strong CP problem

  Junichiro Kawamura; Shohei Okawa; Yuji Omura; Yong Tang

  Journal of High Energy Physics Springer Science and Business Media LLC 2019 (4) 2019/04 [Refereed]
  
• D* polarization vs. RD∗$$ {R}_{D^{\left(\ast \right) } } $$ anomalies in the leptoquark models

  Syuhei Iguro; Teppei Kitahara; Yuji Omura; Ryoutaro Watanabe; Kei Yamamoto

  Journal of High Energy Physics Springer Science and Business Media LLC 2019 (2) 2019/02 [Refereed]
  
• Flavor physics in the multi-Higgs doublet models induced by the left-right symmetry

  Syuhei Iguro; Yu Muramatsu; Yuji Omura; Yoshihiro Shigekami

  Journal of High Energy Physics Springer Science and Business Media LLC 2018 (11) 2018/11 [Refereed]
  
• Test of the $R(D^{(*)})$ anomaly at the LHC

  Syuhei Iguro; Yuji Omura; Michihisa Takeuchi

  Phys. Rev. D 99, 075013 (2019) AMER PHYSICAL SOC 99 (7) 2470-0010 2018/10 [Refereed]
   

  There are discrepancies between the experimental results and the Standard
  Model predictions, in the lepton flavor universality of the semileptonic $B$
  decays: $B \to D^{(*)} \ell \nu$. As the new physics interpretations, new
  charged vector and charged scalar fields, that dominantly couple to the second
  and third generations, have been widely discussed. In this paper, we study the
  signals of the new particles at the LHC, and test the interpretations via the
  direct search for the new resonances. In particular, we see that the $\tau \nu$
  resonance search at the LHC has already covered most of the parameter regions
  favored by the Belle and BaBar experiments. We find that the bound is already
  stronger than the one from the $B_c$ decay depending on the mass of charged
  scalar.
• Status of the semileptonic B decays and muon g-2 in general 2HDMs with right-handed neutrinos

  Syuhei Iguro; Yuji Omura

  Journal of High Energy Physics Springer Verlag 2018 (5) 173  1029-8479 2018/05 [Refereed]
   

  In this paper, we study the extended Standard Model (SM) with an extra Higgs doublet and right-handed neutrinos. If the symmetry to distinguish the two Higgs doublets is not assigned, flavor changing neutral currents (FCNCs) involving the scalars are predicted even at the tree level. We investigate the constraints on the FCNCs at the one-loop level, and especially study the semileptonic B meson decays, e.g. B → D(∗)τ ν and B → K(∗)ll processes, where the SM predictions are more than 2σ away from the experimental results. We also consider the flavor-violating couplings involving right-handed neutrinos and discuss if the parameters to explain the excesses of the semileptonic B decays can resolve the discrepancy in the anomalous muon magnetic moment. Based on the analysis, we propose the smoking-gun signals of our model at the LHC.
• Spontaneous SUSY breaking without R-symmetry in supergravity

  Nobuhiro Maekawa; Yuji Omura; Yoshihiro Shigekami; Manabu Yoshida

  Phys. Rev. D 97, 055015 (2018) 2017/12 [Refereed]
   

  We discuss spontaneous supersymmetry (SUSY) breaking in a model with an
  anomalous $U(1)_A$ symmetry. In this model, the size of the each term in the
  superpotential is controlled by the $U(1)_A$ charge assignment and SUSY is
  spontaneously broken via the Fayet-Iliopoulos of $U(1)_A$ at the meta-stable
  vacuum. In the global SUSY analysis, the gaugino masses become much smaller
  than the sfermion masses, because an approximate R-symmetry appears at the SUSY
  breaking vacuum. In this paper, we show that gaugino masses can be as large as
  gravitino mass, taking the supergravity effect into consideration. This is
  because the R-symmetry is not imposed so that the constant term in the
  superpotential, which is irrelevant to the global SUSY analysis, largely
  contributes to the soft SUSY breaking terms in the supergravity. As the
  mediation mechanism, we introduce the contributions of the field not charged
  under $U(1)_A$ and the moduli field to cancel the anomaly of $U(1)_A$. We
  comment on the application of our SUSY breaking scenario to the GUT models.
• Realization of a spontaneous gauge and supersymmetry breaking vacuum

  Tatsuo Kobayashi; Yuji Omura; Osamu Seto; Kazuki Ueda

  Journal of High Energy Physics Springer Science and Business Media LLC 2017 (11) 2017/11 [Refereed]
  
• Analysis of the TeV-scale mirage mediation with heavy superparticles

  Junichiro Kawamura; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (11) 1029-8479 2017/11 [Refereed]
   

  We discuss effective models derived from a supersymmetric model whose mediation mechanism of supersymmetry (SUSY) breaking is namely mirage mediation. In this model, light higgsino mass, that is required by the natural realization of the electroweak scale, is achieved by the unification of the soft SUSY breaking parameters at the low scale. Besides, we find that extra Higgs fields are also possibly light in some cases. Then, the effective model is a two Higgs doublet model (2HDM) with higgsinos, and it is distinguishable with namely type-II 2HDM which is widely discussed. In this paper, we study the mass spectrum of SUSY particles and the extra Higgs fields, and summarize the phenomenology in the effective model. We survey the current experimental bounds from the LHC and the dark matter experiments as well as the flavor physics. Then, we point out the expected mass scale of the SUSY particles and reveal the future prospects for the direct and indirect searches. We also discuss the difference between our effective model and the 2HDM in the bottom-up approach.
• Interplay between the b to sll anomalies and dark matter physics

  Junichiro Kawamura; Shohei Okawa; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 96 (7) 2470-0010 2017/10 [Refereed]
   

  Recently, the LHCb Collaboration has reported the excesses in the b -> sll processes. One of the promising candidates for new physics to explain the anomalies is the extended Standard Model (SM) with vectorlike quarks and leptons. In that model, Yukawa couplings between the extra fermions and SM fermions are introduced, adding extra scalars. Then, the box diagrams involving the extra fields achieve the b -> sll anomalies. It has been known that the excesses require the large Yukawa couplings of leptons, so that this kind of model can be tested by studying correlations with other observables. In this paper, we consider the extra scalar to be a dark matter (DM) candidate, and investigate DM physics as well as the flavor physics and the LHC physics. The DM relic density and the direct-detection cross section are also dominantly given by the Yukawa couplings, so that we find some explicit correlations between DM physics and the flavor physics. In particular, we find the predictions of the b -> sll anomalies against the direct detection of DM.
• Two-loop anomalous dimensions for four-Fermi operators in supersymmetric theories

  Junji Hisano; Takumi Kuwahara; Yuji Omura; Takeki Sato

  NUCLEAR PHYSICS B ELSEVIER SCIENCE BV 922 77 - 93 0550-3213 2017/09 [Refereed]
   

  We derive two-loop anomalous dimensions for four-Fermi operators in supersymmetric theories using the effective Kahler potential. We introduce the general forms in generic gauge theories and apply our results to the flavor-changing operators in (minimal) supersymmetric standard models. (C) 2017 The Authors. Published by Elsevier B.V.
• Hidden sector behind the CKM matrix

  Shohei Okawa; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 96 (3) 2470-0010 2017/08 [Refereed]
   

  The small quark mixing, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the standard model, may be a clue to reveal new physics around the TeV scale. We consider a simple scenario that extra particles in a hidden sector radiatively mediate the flavor violation to the quark sector around the TeV scale and effectively realize the observed CKM matrix. The lightest particle in the hidden sector, whose contribution to the CKM matrix is expected to be dominant, is a good dark matter (DM) candidate. There are many possible setups to describe this scenario, so that we investigate some universal predictions of this kind of model, focusing on the contribution of DM to the quark mixing and flavor physics. In this scenario, there is an explicit relation between the CKM matrix and flavor violating couplings, such as four-quark couplings, because both are radiatively induced by the particles in the hidden sector. Then, we can explicitly find the DM mass region and the size of Yukawa couplings between the DM and quarks, based on the study of flavor physics and DM physics. In conclusion, we show that DM mass in our scenario is around the TeV scale, and the Yukawa couplings are between Omicron(0.01) and Omicron(1). The spin-independent DM scattering cross section is estimated as Omicron(10(-9)) [pb]. An extra colored particle is also predicted at the Omicron(10) TeV scale.
• Study of dark matter physics in non-universal gaugino mass scenario

  Junichiro Kawamura; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (8) 1029-8479 2017/08 [Refereed]
   

  We study dark matter physics in the Minimal Supersymmetric Standard Model with non-universal gaugino masses at the unification scale. In this scenario, the specific ratio of wino and gluino masses realizes the electro-weak scale naturally and achieves 125 GeV Higgs boson mass. Then, relatively light higgsino is predicted and the lightest neutral particle, that is dominantly given by the neutral component of higgsino, is a good dark matter candidate. The direct detection of the dark matter is sensitive to not only a higgsino mass but also gaugino masses significantly. The upcoming XENON1T experiment excludes the parameter region where bino or gluino is lighter than about 2.5 TeV if the higgsino and the gaugino mass parameters have same signs. We see that the direct detection of dark matter gives stronger bound than the direct search at the LHC experiment when higgsino gives sizable contribution to the dark matter abundance.
• LHCb anomaly and B physics in flavored Z ' models with flavored Higgs doublets

  P. Ko; Yuji Omura; Yoshihiro Shigekami; Chaehyun Yu

  PHYSICAL REVIEW D AMER PHYSICAL SOC 95 (11) 115040  2470-0010 2017/06 [Refereed]
   

  We study an extended Standard Model with a gauged U(1)' flavor symmetry, motivated not only by the fermion mass hierarchy but also by the excesses in B -> K-(*())ll reported by the LHCb collaborations. The U(1)' charges are assigned to quarks and leptons in a flavor-dependent manner, and flavored Higgs doublets are also introduced in order to detail the Yukawa couplings at the renormalizable level. Then, the fermion mass hierarchy is realized by the vacuum alignment of the Higgs doublets. In this model, flavor-changing currents involving the gauge boson of U(1)' and the scalars generated by the Higgs doublets are predicted and the observables in the B -> K-(*())ll process possibly deviate from the Standard Model predictions. We study the possibility that these new flavor-changing interactions can explain the excesses in the B -> K-(*())ll process, and we derive some predictions for the other flavor-violating processes based on the analysis. We specifically investigate the Delta F = 2 processes and the other B decays: e.g., B -> X-s gamma and B -> D-(*())tau nu, where the deviations are reported by the Belle and BABAR collaborations.
• Scale generation via dynamically induced multiple seesaw mechanisms

  Hiroyuki Ishida; Shinya Matsuzaki; Shohei Okawa; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 95 (7) 2470-0010 2017/04 [Refereed]
   

  We propose a model which accounts for the dynamical origin of the electroweak symmetry breaking (EWSB), directly linking to the mass generation of dark matter (DM) candidates and active neutrinos. The standard model (SM) is weakly charged under the U(1)(B-L) gauge symmetry, in conjunction with newly introduced three right-handed Majorana neutrinos and the U(1)(B-L) Higgs. The model is built on the classical scale invariance, that is dynamically broken by a new strongly coupled sector, that is called the hypercolor (HC) sector, which is also weakly coupled to the U(1)(B-L) gauge. At the HC strong scale, the simultaneous breaking of the EW and U(1)(B-L) gauge symmetries is triggered by dynamically induced multiple seesaw mechanisms, namely bosonic seesaw mechanisms. Thus, all of the origins of masses are provided singly by the HC dynamics: that is what we call the dynamical scalegenesis. We also find that a HC baryon, with a mass on the order of a few TeV, can be stabilized by the HC baryon number and the U(1)(B-L) charge, so identified as a DM candidate. The relic abundance of the HC-baryon DM can be produced dominantly via the bosonic-seesaw portal process, and the HC-baryon DM can be measured through the large magnetic moment coupling generated from the HC dynamics, or the U(1)(B-L)-gauge boson portal in direct detection experiments.
• Dark matter physics, flavor physics and LHC constraints in the dark matter model with a bottom partner

  Tomohiro Abe; Junichiro Kawamura; Shohei Okawa; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (3) 1029-8479 2017/03 [Refereed]
   

  In the scenario that dark matter (DM) is a weakly interacting massive particle, there are many possibilities of the interactions with the Standard Model (SM) particles to achieve the relic density of DM. In this paper, we consider a simple DM model where the DM candidate is a complex scalar boson. The model contains a new complex gauge singlet scalar boson and a new fermion whose gauge charge is the same as the right-handed down-type quark. We dub the new fermion the bottom partner. These new particles have Yukawa interactions with the SM down-type quarks. The DM candidate interacts with the SM particles through the Yukawa interactions. The Yukawa interactions are not only relevant to the annihilation process of the DM but also contribute to the flavor physics, such as the Delta F = 2 processes. In addition, the flavor alignment of the Yukawa couplings is related to the decay modes of the bottom partner, and thus we can find the explicit correlations among the physical observables in DM physics, flavor physics, and the signals at the LHC. We survey the Delta F = 2 processes based on the numerical analyses of the thermal relic density, the direct detection of the DM, and the current LHC bounds. We investigate the perturbative bound on the Yukawa coupling as well. A Study of a fermionic DM model with extra scalar quarks is also given for comparison.
• Flavor physics induced by light Z′ from SO(10) GUT

  Junji Hisano; Yu Muramatsu; Yuji Omura; Yoshihiro Shigekami

  Journal of High Energy Physics Springer Science and Business Media LLC 2016 (11) 2016/11 [Refereed]
  
• tau- and mu-physics in a general two Higgs doublet model with mu - tau flavor violation

  Yuji Omura; Eibun Senaha; Kazuhiro Tobe

  PHYSICAL REVIEW D AMER PHYSICAL SOC 94 (5) 2470-0010 2016/09 [Refereed]
   

  Motivated by the recent CMS excess in a flavor violating Higgs decay h -> 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 -> 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 -> mu gamma can be within the reach of the Belle II experiment. We also show that the lepton nonuniversality between tau -> mu nu(nu) over bar and tau -> 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 -> mu l(+)l(-) (l = e, mu), tau -> mu eta, mu -> mu gamma, mu -> 3e and the muon electric dipole moment can be accessible, depending on the unknown Yukawa couplings. On the other hand, the processes like tau -> e gamma and tau -> 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 -> mu tau decay mode, the lepton flavor violating Higgs boson decay modes h -> e mu and h -> e tau are strongly suppressed, and hence it will be difficult to observe these modes at the LHC experiment.
• Threshold corrections to dimension-six proton decay operators in non-minimal SUSY SU(5) GUTs

  Borut Bajc; Junji Hisano; Takumi Kuwahara; Yuji Omura

  NUCLEAR PHYSICS B ELSEVIER SCIENCE BV 910 1 - 22 0550-3213 2016/09 [Refereed]
   

  We calculate the high and low scale threshold corrections to the D = 6 proton decay mode in supersymmetric SU(5) grand unified theories with higher-dimensional representation Higgs multiplets. In particular, we focus on a missing-partner model in which the grand unified group is spontaneously broken by the 75-dimensional Higgs multiplet and the doublet triplet splitting problem is solved. We find that in the missing-partner model the D = 6 proton decay rate gets suppressed by about 60%, mainly due to the threshold effect at the GUT scale, while the SUSY-scale threshold corrections are found to be less prominent when sfermions are heavy. (C) 2016 The Authors. Published by Elsevier B.V.
• Emergent two-Higgs doublet models

  Tomohiro Abe; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (8) 1029-8479 2016/08 [Refereed]
   

  We investigate origin of three features that are often assumed in analysis of two-Higgs doublet models: (i) softly broken Z(2) symmetry, (ii) CP invariant Higgs potential, and (iii) degenerated mass spectra. We extend electroweak gauge symmetry, introducing extra gauge symmetry and extra scalars, and we show that our models effectively derive two-Higgs doublet models at low energy which naturally hold the three features. We also find that the models can solve the strong CP problem.
• Diphoton excess at 750 GeV and LHC constraints in models with vectorlike particles

  Junichiro Kawamura; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 93 (11) 2470-0010 2016/06 [Refereed]
   

  Recently, the ATLAS and CMS collaborations report excesses around 750 GeVin the diphoton channels. This might be the evidence which reveals newphysics beyond the Standard Model. In this paper, we consider models with a 750 GeV scalar and vectorlike particles, which couple each other through Yukawa couplings. The decay of the scalar to diphoton is given by the loop diagrams involving the extra colored particles. We investigate not only the setup required by the excesses, but also the LHC constraints, especially concerned with the vectorlike particles. In our scenario, the extra colored particles decay to quarks and a dark matter (DM) via Yukawa couplings. Then, the signals from the vectorlike particles are dijet, b (b) over bar and/or t (t) over bar with large missing energy. We discuss two possibilities for the setups: One is a model with vectorlike fermions and a scalar DM, and the other is a model with vectorlike scalars and a fermionic DM. We suggest the parameter region favored by the excess in each case, and study the constraints based on the latest LHC results at root s = 8 TeV and 13 TeV. We conclude that the favored region is almost excluded by the LHC bounds, especially when the 750 GeVscalar dominantly decays to DMs. The mass differences between the vectorlike particles and theDMshould be less than O(100) GeV [O(10) GeV] to realize the large diphoton signal and the large decay width, if the extra colored particle only decays to a top (bottom) quark and a dark matter. Otherwise, these scenarios are already excluded by the latest LHC results.
• Diphoton excess at 750 GeV in leptophobic U(1)' model inspired by E-6 GUT

  P. Ko; Yuji Omura; Chaehyun Yu

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (4) 1029-8479 2016/04 [Refereed]
   

  We discuss the 750 GeV diphoton excess at the LHCA@13TeV in the framework of leptophobic U(1)' model inspired by E-6 grand unified theory (GUT). In this model, the Standard Model (SM) chiral fermions carry charges under extra U(1)' gauge symmetry which is spontaneously broken by a U(1)'-charged singlet scalar (Phi)). In addition, extra quarks and leptons are introduced to achieve the anomaly -free conditions, which is a natural consequence of the assumed E-6 GUT. These new fermions are vectorlike under the SM gauge group but chiral under new U(1)', and their masses come entirely from the nonzero vacuum expectation value of Phi through the Yukawa interactions. Then, the CP-even scalar h(Phi) from Phi can be produced at the LHC by the gluon fusion and decay to the diphoton via the one -loop diagram involving the extra quarks and leptons, and can be identified as the origin of diphoton excess at 750 GeV. In this model, h(Phi), can decay into a pair of dark matter particles as well as a pair of scalar bosons, thereby a few tens of the decay width may be possible.
• Constraints on nonuniversal gaugino mass scenario using the latest LHC data

  Junichiro Kawamura; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 93 (5) 2470-0010 2016/03 [Refereed]
   

  We investigate exclusion limits on the nonuniversal gaugino mass scenario in the minimal supersymmetric standard model (MSSM), according to the latest results of the superparticle search at the LHC8 and the LHC13. In this scenario, suitable ratios of wino to gluino mass can realize the observed value of the Higgs boson mass, while keeping a small mu parameter. Such a small mu parameter corresponds to the mass of Higgsino, so that lightest neutralino and chargino are Higgsino-like and their masses are almost degenerate. Besides, we find that the right-handed top squark tends to be lighter than other sfermions and then the top squark search, where the top squark decays to a quark and Higgsino, is relevant to our model. In our analysis, the exclusion limits are derived using the data of the top squark searches in the bb + E-T(miss) and tb + E-T(miss) channels. Furthermore, the exclusion limit on gluino mass, which is crucial to our scenario, is investigated as well. The analysis of the gluino is based on the data of the analysis with large missing energy and at least three b-tagged jets at the ATLAS experiment.
• Study of lepton flavor violation in flavor symmetric models for lepton sector

  Tatsuo Kobayashi; Yuji Omura; Fumihiro Takayama; Daiki Yasuhara

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (10) 1029-8479 2015/10 [Refereed]
   

  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(-) -> e(+)mu(-)mu(-)(mu(+)e(-)e(-)) and e(+)e(-) -> 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 -> 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.
• Survey of Higgs interpretations of the diboson excesses

  Yuji Omura; Kazuhiro Tobe; Koji Tsumura

  Physical Review D - Particles, Fields, Gravitation and Cosmology American Physical Society 92 (5) 1550-2368 2015/09 [Refereed]
   

  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.
• Threshold corrections to baryon number violating operators in supersymmetric SU(5) GUTs

  Junji Hisano; Takumi Kuwahara; Yuji Omura

  NUCLEAR PHYSICS B ELSEVIER SCIENCE BV 898 1 - 29 0550-3213 2015/09 [Refereed]
   

  The nucleon decay is a significant phenomenon to verify grand unified theories (GUTs). For the precise prediction of the nucleon lifetime induced by the gauge bosons associated with the unified gauge group, it is important to include the renormalization effects on the Wilson coefficients of the dimension-six baryon number violating operators. In this study, we have derived the threshold corrections to these coefficients at the one-loop level in the minimal supersymmetric SU(5) GUT and the extended one with additional SU(5) vector-like pairs. As a result, it is found that the nucleon decay rate is suppressed about 5% in the minimal setup, and then the suppression could be O(10)% in the vector-like matter extensions. (C) 2015 The Authors. Published by Elsevier B.V.
• Interpretations of the ATLAS diboson resonances

  Junji Hisano; Natsumi Nagata; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 92 (5) 1550-7998 2015/09 [Refereed]
   

  The ATLAS Collaboration has reported excesses in searches for resonant diboson production decaying into hadronic final states. This deviation from the standard model prediction may be a signature of an extra bosonic particle having a mass of around 2 TeV with a fairly narrow width, which implies the presence of a new perturbative theory at the TeV scale. In this paper, we study interpretations of the signal and its implication to physics beyond the standard model. We find that the resonance could be regarded as a leptophobic vector particle, which could explain a part of the observed excesses without conflict with the present constraints from other direct searches for heavy vector bosons at the LHC as well as the electroweak precision measurements.
• Survey of Higgs interpretations of the diboson excesses

  Yuji Omura; Kazuhiro Tobe; Koji Tsumura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 92 (5) 2470-0010 2015/09 [Refereed]
   

  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.
• LHC phenomenology of natural MSSM with non-universal gaugino masses at the unification scale

  Hiroyuki Abe; Junichiro Kawamura; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (8) 1029-8479 2015/08 [Refereed]
   

  In this letter, we study collider phenomenology in the supersynamtric Standard Model with a certain type of non-universal gaugino masses at the gauge coupling unification scale, motivated by the little hierarchy problem. In this scenario, especially the wino mass is relatively large compared to the gluino mass at the unification scale, and the heavy wino can relax the fine-tuning of the higgsino mass parameter, so-called mu-parameter. Besides, it will enhance the lightest Higgs boson mass due to the relatively large left-right mixing of top squarks through the renorrnalization group (RG) effect. Then 125 GeV Higgs boson could be accomplished, even if the top squarks are lighter than 1 TeV and the mu parameter is within a few hundreds GeV. The right-handed top squark tends to be lighter than the other sfermions due to the RU runnings, then we focus on the top squark search at the LHC. Since the top squark is almost right-handed and the higgsinos are nearly degenerate, 2b + E-T(miss) channel is the most sensitive to this scenario. We figure out current and expected experimental bounds on the lightest top squark mass and model parameters at the gauge coupling unification scale.
• Higgs and dark matter physics in the type-II two-Higgs-doublet model inspired by E-6 GUT

  P. Ko; Yuji Omura; Chaehyun Yu

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (6) 1029-8479 2015/06 [Refereed]
   

  We study Higgs and dark matter physics in the type-II two-Higgs-doublet model (2HDM) with an extra U(1)(H) gauge symmetry, inspired by the E-6 grand unified theory (GUT). From the viewpoint of the bottom-up approach, the additional U(1)(H) gauge symmetry plays a crucial role in avoiding the tree-level flavor changing neutral currents mediated by neutral Higgs bosons in general 2HDMs. In the model with U(1)(H) gauge symmetry, which has Type-II Yukawa couplings, we have to introduce additional chiral fermions that are charged under the U(1)(H) gauge symmetry as well as under the Standard-Model (SM) gauge symmetry in order to cancel chiral gauge anomalies. For the U(1)(H) charge assignment and the extra matters, we adopt the ones inspired by the E-6 GUT: the extra quark-like and lepton-like fermions with the non-trivial U(1)(H) charges. We discuss their contributions to the physical observables, such as the measurements of Higgs physics and electro-weak interactions, and investigate the consistency with the experimental results. Furthermore, we could find extra neutral particles like the SM neutrinos after the electro-weak symmetry breaking, and they could be stable, because of the remnant symmetry after U(1)(H) symmetry breaking. We also discuss the thermal relic density and the (in)direct-detections of this dark matter candidate.
• Lepton-flavor-violating Higgs decay h -> mu tau and muon anomalous magnetic moment in a general two Higgs doublet model

  Yuji Omura; Eibun Senaha; Kazuhiro Tobe

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (5) 1029-8479 2015/05 [Refereed]
   

  A two Higgs doublet model (2HDM) is one of minimal extensions of the Standard Model (SM), and it is well-known that the general setup predicts the flavor-violating phenomena, nwdiated by neutral Higgs interactions. Recently the CMS collaboration has reported an excess of the lepton-flavor-violating Riggs decay in h -> mu tau channel with a. significance of 2.4 sigma. We investigate the CMS excess in a general 2HDM with tree-level Flavor Changing Neutral Currents (FCNCs), and discuss its impact on the other physical observations. Especially, we see that the FCNCs relevant to the excess can enhance the neutral Higgs contributions to the muon anomalous magnetic moment, and can resolve the discrepancy between the measured value and the SM prediction. We also find that the couplings to be consistent with the anomaly of the muon magnetic moment as well as the CMS excess in h -> mu tau predict the sizable rate of tau -> mu gamma, which is within the reach of future B factory.
• Flavor violating Z ' from SO(10) SUSY GUT in High-Scale SUSY

  Junji Hisano; Yu Muramatsu; Yuji Omura; Masato Yamanaka

  PHYSICS LETTERS B ELSEVIER SCIENCE BV 744 395 - 400 0370-2693 2015/05 [Refereed]
   

  We propose an SO(10) supersymmetric grand unified theory (SUSY GUT), where the SO(10) gauge symmetry breaks down to SU(3)(c) x SU(2)(L)x U(1)(Y) x U(1)(X) at the GUT scale and U(1)(X) is radiatively broken at the SUSY-braking scale. In order to achieve the observed Higgs mass around 126 GeV and also to satisfy constraints on flavor-and/or CP-violating processes, we assume that the SUSY-breaking scale is O(100) TeV, so that the U(1)(X) breaking scale is also O(100) TeV. One big issue in the SO(10) GUTs is how to realize realistic Yukawa couplings. In our model, not only 16-dimensional but also 10-dimensional matter fields are introduced to predict the observed fermion masses and mixings. The Standard-Model quarks and leptons are linear combinations of the 16-and 10-dimensional fields so that the U(1)(X) gauge interaction may be flavor-violating. We investigate the current constraints on the flavor-violating Z' interaction from the flavor physics and discuss prospects for future experiments. (C) 2015 The Authors. Published by Elsevier B.V.
• Unification of SUSY breaking and GUT breaking

  Tatsuo Kobayashi; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (2) 1 - 24 1029-8479 2015/02 [Refereed]
   

  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.
• Dark matter and dark force in the type-I inert 2HDM with local U(1)(H) gauge symmetry

  P. Ko; Yuji Omura; Chaehyun Yu

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (11) 1029-8479 2014/11 [Refereed]
   

  We discuss dark matter (DM) physics in the Type-I inert two-Higgs-doublet model (2HDM) with local U(1) H Higgs gauge symmetry, which is assigned to the extra Higgs doublet in order to avoid the Higgs-mediated flavor problems. In this gauged inert DM setup, a U(1)(H)-charged scalar Phi is also introduced to break U(1)(H) spontaneously through its nonzero vacuum expectation value (VEV), <Phi >, and then the remnant discrete subgroup appears according to the U(1)(H) charge assignment of Phi. The U(1)(H)-charged Higgs doublet does not have Yukawa couplings with the Standard-Model (SM) fermions, and its lightest neutral scalar component H is stable because of the remnant discrete symmetry. In order to suppress a too large Z-exchange diagram contribution in DM direct detection experiments, we have to introduce a non-renormalizable operator which can be generated by integrating out an extra heavy scalar. With these new particles contents, we first investigate the constraint on the U(1)(H) gauge interaction, especially through the kinetic and mass mixing between the SM gauge bosons and the extra gauge boson. Then we discuss dark matter physics in our 2HDM: thermal relic density, and direct/indirect detections of dark matter. The additional U(1) (H) gauge interaction plays a crucial role in reducing the DM thermal relic density. The most important result within the inert DM model with local U(1)(H) symmetry is that similar to O(10) GeV dark matter scenario, which is strongly disfavored in the usual Inert Doublet Model (IDM) with Z(2) symmetry, is revived in our model because of newly open channels, HH -> Z(H)Z(H), Z(H)Z. Exotic Higgs decays, h -> Z(H)Z(H), ZZ(H), would be distinctive signatures of the inert 2HDM with local U(1)(H) symmetry.
• Revisiting discrete dark matter model: theta(13) not equal 0 and v(R) dark matter

  Yuta Hamada; Tatsuo Kobayashi; Atsushi Ogasahara; Yuji Omura; Fumihiro Takayama; Daiki Yasuhara

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (10) 1029-8479 2014/10 [Refereed]
   

  We revisit the discrete dark matter model with the A(4) flavor symmetry originally introduced by M.Hirsch et. al. We show that radiative corrections can lead to non-zero theta(13) and the non-zero mass for the lightest neutrino. We find an interesting relation among neutrino mixing parameters and it indicates the sizable deviation of s(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 that the thermal freeze-out explains observed dark matter abundance, TeV-scale right-handed neutrino and flavored scalar bosons are required. In such a case, the flavor symmetry plays an important role for the suppression of lepton flavor violating processes as well as for the stability of dark matter. We show that this scenario is viable within currently existing constraints from collider, low energy experiments and cosmological observations.
• Higgs phenomenology in Type-I 2HDM with U(1)(H) Higgs gauge symmetry

  P. Ko; Yuji Omura; Chaehyun Yu

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (1) 1029-8479 2014/01 [Refereed]
   

  It is well known that generic two-Higgs-doublet models (2HDMs) suffer from potentially large Higgs-mediated flavor-changing neutral current (FCNC) problem, unless additional symmetries are imposed on the Higgs fields thereby respecting the Natural Flavor Conservation Criterion (NFC) by Glashow and Weinberg. A common way to respect the NFC is to impose Z(2) symmetry which is softly broken by a dim-2 operator. Another new way is to introduce local U(1)(H) Higgs flavor symmetry that distinguishes one Higgs doublet from the other. In this paper, we consider the Higgs phenomenology in Type-I 2HDMs with the U(1)(H) symmetry with the simplest U(1)(H) assignments that the SM fermions are all neutral under U(1)(H), and we make detailed comparison with the ordinary Type-I 2HDM. After imposing various constraints such as vacuum stability and perturbativity as well as the electroweak precision observables and collider search bounds on charged Higgs boson, we find that the allowed Higgs signal strengths in our model are much broader than those in the ordinary Type-I 2HDM, because of newly introduced U(1)(H)-charged singlet scalar and U(1)(H) gauge boson. Still the ATLAS data on gg -> h -> gamma gamma cannot be accommodated. Our model could be distinguished from the ordinary 2HDM with the Z(2) symmetry in a certain parameter region and some channels. If the couplings of the new boson turn out to be close to those in the SM, it would be essential to search for extra U(1)(H) gauge boson and/or one more neutral scalar boson to distinguish two models.
• Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries

  Mu-Chun Chen; Maximilian Fallbacher; Yuji Omura; Michael Ratz; Christian Staudt

  NUCLEAR PHYSICS B ELSEVIER SCIENCE BV 873 (2) 343 - 371 0550-3213 2013/08 [Refereed]
   

  In a class of supersymmetric flavor models predictions are based on residual symmetries of some subsectors of the theory such as those of the charged leptons and neutrinos. However, the vacuum expectation values of the so-called flavon fields generally modify the Kahler potential of the setting, thus changing the predictions. We derive simple analytic formulae that allow us to understand the impact of these corrections on the predictions for the masses and mixing parameters. Furthermore, we discuss the effects on the vacuum alignment and on flavor changing neutral currents. Our results can also be applied to non-supersymmetric flavor models. (C) 2013 Elsevier B.V. All rights reserved.
• B -> D^(*) tau nu and B -> tau nu in chiral U(1)' models with flavored multi Higgs doublets

  P. Ko; Yuji Omura; Chaehyun Yu

  JHEP 1303 (2013) 151 2013/03 [Refereed]
   

  We discuss semileptonic and leptonic B decays, B to D^{(*)} tau nu and B to
  tau nu, in the chiral U(1)' models which were proposed by the present authors
  in the context of the top forward-backward asymmetry (A^t_FB) observed at the
  Tevatron. In these models, extra Higgs doublets with nonzero U(1)' charges are
  required in order to make the realistic mass matrix for up-type quarks. Then
  the extra (pseudo)scalars contribute to A^t_FB with large flavor-changing
  Yukawa couplings involving top quark. The contribution of the charged Higgs to
  A^t_FB is negligible, but it may significantly affect B decays: especially, B
  to D^(*) tau nu and B to tau nu. We investigate constraints on the B decays,
  based on the recent results in BaBar and Belle experiments, and discuss the
  possibility that the allowed parameter region in the B decays can achieve large
  A^t_ FB.
• A resolution of the flavor problem of two Higgs doublet models with an extra U(1)(H) symmetry for Higgs flavor

  P. Ko; Yuji Omura; Chaehyun Yu

  PHYSICS LETTERS B ELSEVIER SCIENCE BV 717 (1-3) 202 - 206 0370-2693 2012/10 [Refereed]
   

  We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)(H) gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)(H) charges. Then one can easily avoid the tree-level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z(2) symmetry, and the pseudoscalar boson could be eaten by extra Z(H) boson. Imposing the anomaly cancellation, we find that the U(1)(H) in the Type-II and Type-IV 2HDMs become leptophobic and leptophilic, respectively. For the Type-I case, U(1)(H) depends on two parameters, and some simple cases include U(1)(H) = U(1)(B-L), U(1)(R), or U(1)(Y). We sketch qualitative phenomenology of these models. (C) 2012 Elsevier B.V. All rights reserved.
• Top forward-backward asymmetry and the CDF Wjj excess in leptophobic U(1)' flavor models

  P. Ko; Yuji Omura; Chaehyun Yu

  PHYSICAL REVIEW D AMER PHYSICAL SOC 85 (11) 1550-7998 2012/06 [Refereed]
   

  We construct anomaly-free leptophobic U(1)' flavor models with light Z '(similar to 145 GeV). In order to allow renormalizable Yukawa interactions for the standard model chiral fermions, new Higgs doublets with nonzero U(1)' charges are introduced. Then the neutral (pseudo) scalar Higgs bosons as well as Z ' contribute to the t (t) over bar and the same sign top pair productions [sigma(t (t) over bar) and sigma(tt)], and one can evade the strong constraint from sigma(tt). The top forward-backward asymmetry (A(FB)) and Wjj excess at CDF could be accommodated by A(FB)(New) = 0.084 similar to 0.12 and sigma(Wjj) less than or similar to O(10) pb X sin(2)2 beta.
• Dijet resonance from leptophobic Z ' and light baryonic cold dark matter

  P. Ko; Yuji Omura; Chaehyun Yu

  PHYSICS LETTERS B ELSEVIER SCIENCE BV 710 (1) 197 - 200 0370-2693 2012/03 [Refereed]
   

  In light of the recent CDF report on the excess in the Wjj channel, we analyze (non)supersymmetric U(1)(B) x U(1)(l) model, interpreting the dijet peak as a leptophobic U(1)(B) gauge boson. If this excess is confirmed, it has an interesting implication for the baryonic cold dark matter (CDM) in the model: there should be light CDM with a few GeV mass, and direct detection cross section at the level of a few x 10(-2) pb. (C) 2012 Elsevier B.V. All rights reserved.
• Light dark matter in leptophobic Z ' models

  P. Gondolo; P. Ko; Y. Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 85 (3) 2470-0010 2012/02 [Refereed]
   

  Recent experimental results in direct dark matter detection may be interpreted in terms of a dark matter particle of mass around 10 GeV/c(2). We show that the required scenario can be realized with a new dark matter particle charged under an extra Abelian gauge boson Z' that couples to quarks but not leptons. This is possible provided the Z' gauge boson is very light, around 10-20 GeV/c(2) in mass, and the gauge coupling constant is small, alpha' similar to 10(-5). Such scenarios are not constrained by accelerator data.
• Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj

  P. Ko; Yuji Omura; Chaehyun Yu

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (1) 1029-8479 2012/01 [Refereed]
   

  We present U(1) flavor models for leptophobic Z' with flavor dependent couplings to the right-handed up-type quarks in the Standard Model (SM), which can accommodate the recent data on the top forward-backward (FB) asymmetry and the dijet resonance associated with a W boson reported by CDF Collaboration. Such flavor-dependent leptophobic charge assignments generally require extra chiral fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor symmetry calls for new U(1)'-charged Higgs doublets in order for the SM fermions to have realistic renormalizable Yukawa couplings. The stringent constraints from the top FB asymmetry at the Tevatron and the same sign top pair production at the LHC can be evaded due to contributions of the extra Higgs doublets. We also show that the extension could realize cold dark matter candidates.
• Supersymmetric U(1)(B) x U(1)(L) model with leptophilic and leptophobic cold dark matters

  P. Ko; Y. Omura

  PHYSICS LETTERS B ELSEVIER SCIENCE BV 701 (3) 363 - 366 0370-2693 2011/07 [Refereed]
   

  We consider a supersymmetric model with extra U(1)(B) x U(1)(L) gauge symmetry that is broken spontaneously. Salient features of this model are that there are three different types of cold dark matter (CDM) candidates, and neutral scalar sector has a rich structure. Light CDM with sigma(Sl) similar to 10(-3+/-1) pb can be easily accommodated by leptophobic dark matter (chi(B)) with correct relic density, if the U(1)(B) gauge boson mass is around 2m(chi B). Also the PAMELA and Fermi/EAT data can be fit by leptophilic CDM with mass similar to 1 TeV. There could be interesting signatures of new fermions and new gauge bosons at the LHC. (C) 2011 Elsevier B.V. All rights reserved.
• Supersymmetry breaking, R-symmetry, and conformal dynamics

  Yuji Omura

  2009/03 

  We study N=1 global and local supersymmetric theories with a continuous
  global U(1)_R symmetry. We discuss conditions for supersymmetry (SUSY) breaking
  and vacuum structures of R-symmetric SUSY models. Especially we find the
  conditions for R-symmetry breaking and runway vacua in global supersymmetric
  theories. We introduce explicit R-symmetry breaking terms into such models in
  global and local supersymmetric theories. We classify explicit R-symmetry
  breaking terms by the structure of newly appeared SUSY stationary points as a
  consequence of the R-breaking effect. Based on the generic argument, we propose
  the scenario that conformal dynamics causes approximate R-symmetry and
  metastable SUSY breaking vacua at a low energy scale. Furthermore, we find that
  conformal dynamics also leads approximate R-symmetry in softly SUSY breaking
  theories, even in more complicated models such as the duality cascade. We
  investigate the RG flow of SUSY breaking terms as well as supersymmetric
  couplings in the duality cascade of softly broken supersymmetric theories. We
  also show the possibility that cascading would be terminated by the gauge
  symmetry breaking, which is induced by the so-called B-term. Finally, we find
  some models to arrive at standard-model-like models and to cause gauge symmetry
  breaking corresponding to electro-weak symmetry breaking.
• Duality cascade of softly broken supersymmetric theories

  Hiroyuki Abe; Tetsutaro Higaki; Tatsuo Kobayashi; Kazutoshi Ohta; Yuji Omura; Haruhiko Terao

  PHYSICAL REVIEW D AMER PHYSICAL SOC 79 (4) 2470-0010 2009/02 [Refereed]
   

  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.
• Flavor symmetry breaking and vacuum alignment on orbifolds

  Tatsuo Kobayashi; Yuji Omura; Koichi Yoshioka

  PHYSICAL REVIEW D AMER PHYSICAL SOC 78 (11) 1550-7998 2008/12 [Refereed]
   

  Flavor symmetry has been widely studied for figuring out the masses and mixing angles of standard model fermions. In this paper we present a framework for handling flavor symmetry breaking where the symmetry breaking is triggered by boundary conditions of scalar fields in extra-dimensional space. The alignment of scalar expectation values is achieved without referring to any details of scalar potential and its minimization procedure. As applications to non-Abelian discrete flavor symmetries, illustrative lepton mass models are constructed where the S-3 and A(4) flavor symmetries are broken down to the directions leading to the tribimaximal form of lepton mixing and realistic mass patterns.
• Soft supersymmetry breaking terms from A(4) lepton flavor symmetry

  Hajime Ishimori; Tatsuo Kobayashi; Yuji Omura; Morimitsu Tanimoto

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (12) 1029-8479 2008/12 [Refereed]
   

  We study the supersymmetric model with the A(4) lepton flavor symmetry, in particular soft supersymmetry breaking terms, which are predicted from the A(4) lepton flavor symmetry. We evaluate soft slepton masses and A-terms within the framework of supergravity theory. Constraints due to experiments of flavor changing neutral current processes are examined.
• Soft supersymmetry breaking terms from D(4) x Z(2) lepton flavor symmetry

  Hajime Ishimori; Tatsuo Kobayashi; Hiroshi Ohki; Yuji Omura; Ryo Takahashi; Morimitsu Tanimoto

  PHYSICAL REVIEW D AMER PHYSICAL SOC 77 (11) 1550-7998 2008/06 [Refereed]
   

  We study the supersymmetric model with D(4) x Z(2) lepton flavor symmetry. We evaluate soft supersymmetry breaking terms, i.e., soft slepton masses and A-terms, which are predicted in the D(4) flavor model. We consider constraints due to experiments of flavor-changing neutral current processes.
• Dynamically sequestered F-term uplifting in extra dimension

  Hiroyuki Abe; Tetsutaro Higaki; Tatsuo Kobayashi; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (4) 1029-8479 2008/04 [Refereed]
   

  We study moduli stabilization, the dynamical supersymmetry (SUSY) breaking, the uplifting of SUSY anti-de Sitter (AdS) vacuum and the sequestering of hidden sector in a five-dimensional supergravity model, where all modes of the visible sector and the hidden sector are originated from bulk fields. We clarify couplings between the visible and hidden sectors. The expressions for the visible sector soft SUSY breaking terms as well as the hidden sector potential are shown explicitly in our model. The sequestering is achieved dynamically by a wavefunction localization in extra dimension. We find that the tree-level soft scalar mass and the A-term can be suppressed at a SUSY breaking Minkowski minimum where the radius modulus is stabilized, while gaugino masses would be a mirage type.
• D-4 flavor symmetry for neutrino masses and mixing

  Hajime Ishimoria; Tatsuo Kobayashi; Hiroshi Ohki; Yuji Omura; Ryo Takahashi; Morimitsu Tanimoto

  PHYSICS LETTERS B ELSEVIER SCIENCE BV 662 (2) 178 - 184 0370-2693 2008/04 [Refereed]
   

  We present the D-4 x Z(2) flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed. (C) 2008 Elsevier B.V. All rights reserved.
• Metastable supersymmetry breaking vacua from conformal dynamics

  Hiroyuki Abe; Tatsuo Kobayashi; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 77 (6) 1550-7998 2008/03 [Refereed]
   

  We study the scenario that conformal dynamics leads to metastable supersymmetry breaking vacua. At a high energy scale, the superpotential is not R-symmetric and has a supersymmetric minimum. However, conformal dynamics suppresses several operators along renormalization group flow toward the infrared fixed point. Then we can find an approximately R-symmetric superpotential, which has a metastable supersymmetry breaking vacuum, and the supersymmetric vacuum moves far away from the metastable supersymmetry breaking vacuum. We show a 4D simple model. Furthermore, we can construct 5D models with the same behavior, because of the AdS/CFT duality.
• R-symmetry, supersymmetry breaking and metastable vacua in global and local supersymmetric theories

  Hiroyuki Abe; Tatsuo Kobayashi; Yuji Omura

  JOURNAL OF HIGH ENERGY PHYSICS SPRINGER (11) 1029-8479 2007/11 [Refereed]
   

  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.
• Relaxed fine-tuning in models with nonuniversal gaugino masses

  Hiroyuki Abe; Tatsuo Kobayashi; Yuji Omura

  PHYSICAL REVIEW D AMER PHYSICAL SOC 76 (1) 2470-0010 2007/07 [Refereed]
   

  We study, in a bottom-up approach, the fine-tuning problem between soft supersymmetry (SUSY) breaking parameters and the mu term for the successful electroweak symmetry breaking in the minimal supersymmetric standard model. It is shown that certain ratios among nonuniversal gaugino masses at the grand unified theory (GUT) scale are necessary to reduce fine-tuning. In addition, when all the gaugino masses are regarded as independent ones in their origins, a small gluino mass M-3 less than or similar to 120 GeV and a nonvanishing A term A(t)similar to O(M-3) associated with top squarks are also required at the GUT scale as well as the nonuniversality. On the other hand, when we consider some UV theory, which fixes ratios of soft SUSY breaking parameters as certain values aside from the overall magnitude, heavier spectra are allowed. It is favored that the gluino and W-ino masses are almost degenerate at the weak scale, while a wider region of b-ino mass is favorable.
• Moduli stabilization, F-term uplifting, and soft supersymmetry breaking terms

  Hiroyuki Abe; Tetsutaro Higaki; Tatsuo Kobayashi; Yuji Omura

  PHYSICAL REVIEW D AMERICAN PHYSICAL SOC 75 (2) 1550-7998 2007/01 [Refereed]
   

  We study moduli stabilization with F-term uplifting. As a source of uplifting F-term, we consider spontaneous supersymmetry breaking models, e.g. the Polonyi model and the Intriligator-Seiberg-Shih model. We analyze potential minima by requiring almost vanishing vacuum energy and evaluate the size of modulus F-term. We also study soft SUSY-breaking terms. In our scenario, the mirage mediation is dominant in gaugino masses. Scalar masses can be comparable with gaugino masses or much heavier, depending on couplings with spontaneous supersymmetry breaking sector.
• Dynamical realization of democratic Yukawa matrices and alignment of A terms

  Tatsuo Kobayashi; Yuji Omura; Haruhiko Terao

  PHYSICAL REVIEW D AMERICAN PHYSICAL SOC 74 (5) 1550-7998 2006/09 [Refereed]
   

  We study realization of the democratic form of Yukawa matrices by infrared fixed points. We investigate renormalization-group flows of Yukawa couplings in models with a single Yukawa matrix for three families, and up and down-sector Yukawa matrices. It is found that each model has its certain pattern of renormalization-group flows of Yukawa matrices. We apply them to the charged lepton sector and quark sector, and examine in which situation our class of models can lead to realistic results for the mass ratios and mixing angles between the second and third families. We also study corresponding A-terms. The A-terms approach toward the universal form with no physical CP-violating phase. Thus, constraints due to various neutral flavor changing processes except for mu -> e gamma are found to be satisfied by this dynamics. In order to suppress the electric dipole moments as well as mu -> e gamma sufficiently, more alignment of the A-terms with some reason is required.

Books etc

• 素粒子の風味に異変？ーB中間子にまつわる謎

  大村雄司 日本物理学会誌74巻3号「話題」記事 2019/03

Conference Activities & Talks

• Light lepton portal dark matter meets the LHC  [Not invited]

  Yuji Omura

  HPNP2023  2023/06
• Chasing the two-Higgs doublet model in the di-Higgs production  [Invited]

  YUJI OMURA

  the 36th Regular Meeting of the New Higgs Working Group  2023/02
• TeV-scale vector leptoquark from Pati-Salam unification with vectorlike families  [Not invited]

  Yuji Omura

  Summer Institute 2022  2022/09
• TeV-scale vector leptoquark from Pati-Salam unification with vectorlike families  [Not invited]

  Yuji Omura

  日本物理学会 第77回年次大会  2022/03
• Light mass window of lepton portal dark matter  [Invited]

  Yuji Omura

  New Higgs Working Group the 31st meeting  2021/11
• Light mass window of lepton portal dark matter

  Yuji Omura

  素粒子現象論研究会2021  2021/11
• Impact of light dark matter on Higgs physics

  Yuji Omura

  ILC Workshop on Potential Experiments (ILCX2021)  2021/10
• Light mass window of lepton portal dark matter

  Yuji Omura

  HPNP2021  2021/03
• Light mass window of lepton portal dark matter

  Yuji Omura

  「ニュートリノで拓く素粒子と宇宙」研究会２０２０  2020/12
• フレーバーアノマリーの背後にひそむ理論

  大村雄司

  日本物理学会2020年秋季大会  2020/09
• Summary of lepton portal dark matter  [Not invited]

  Yuji Omura

  KEK-PH 2020  2020/02
• Interplay between flavor physics and the direct search for new physics  [Invited]

  Yuji Omura

  The 1st Asian-European-Institutes (AEI) Workshop for BSM and the KIAS Workshop on Particle Physics and Cosmology  2019/11
• WIMP dark matter expected in the parity solution to the strong CP problem  [Not invited]

  Yuji Omura

  Scalars 2019  2019/09
• WIMP dark matter expected in the parity solution to the strong CP problem  [Not invited]

  Yuji Omura

  Summer Institute 2019  2019/08
• Interplay between LHC and flavors  [Not invited]

  Yuji Omura

  The 4th KMI International Symposium  2019/02
• Status of the semileptonic B decays and muon g-2 in general 2HDMs  [Invited]

  Yuji Omura

  BrAinstorming on paRticle physics and Astrophysics phenoMenology  2018/03
• Hidden sector behind the quark mixing  [Invited]

  Yuji Omura

  KEK Theory Meeting on Particle Physics Phenomenology  2018/02
• The New physics interpretations of the b to s ll anomalies and the impact on dark matter physics  [Invited]

  Yuji Omura

  The 21st LHC Physics Monthly Meeting: B- and K-physics anomalies  2017/07
• τ- and μ-physics in a general two Higgs doublet model with μ-τ flavor violation  [Not invited]

  Yuji Omura

  日本物理学会 第71回年次大会  2016/03
• The Diphoton Excess at 750 GeV in models with vector-like particles  [Not invited]

  Yuji Omura

  Interplay between LHC and Flavor Physics  2016/03
• The Diphoton Excess at 750 GeV in models with vector-like particles  [Not invited]

  Yuji Omura

  KEK-PH 2016  2016/02
• Flavor violating Z' from SO(10) SUSY GUT in High-Scale SUSY  [Not invited]

  Yuji Omura

  Dark Side of the Universe 2015  2015/12
• Lepton-flavor-violating Higgs decay h to mu tau and muon anomalous magnetic moment in a general two Higgs doublet model  [Not invited]

  Yuji Omura

  KIAS-CFHEP Workshop and the 5th KIAS workshop on Particle Physics and Cosmology  2015/11
• Lepton-flavor-violating Higgs decay h to mu tau and muon anomalous magnetic moment in a general two Higgs doublet model  [Not invited]

  Yuji Omura

  日本物理学会 秋季大会  2015/09
• Interpretations of the ATLAS Diboson Resonances  [Invited]

  Yuji Omura

  KMI - IPAP workshop  2015/08
• Low-scale SUSY scenarios toward the LHC Run-II  [Invited]

  大村 雄司

  新学術領域研究会テラスケール2015  2015/06
• Flavor violating Z' from SO(10) SUSY GUT in High-Scale SUSY  [Not invited]

  Yuji Omura

  Flavor Physics ＆ CP violation 2015  2015/05
• Unification of SUSY breaking and GUT breaking  [Not invited]

  Yuji Omura

  日本物理学会 第70回年次大会  2015/03
• Unification of SUSY breaking and GUT breaking  [Not invited]

  Yuji Omura

  Origin of Mass and Strong Coupling Gauge Theories  2015/03
• Unification of SUSY breaking and GUT breaking  [Not invited]

  Yuji Omura

  Higgs as a Probe of New Physics 2015  2015/02
• Unification of SUSY breaking and GUT breaking  [Not invited]

  Yuji Omura

  The 4rd KIAS workshop on Particle Physics and Cosmology  2014/10
• Dark matter physics in 2HDMs  [Not invited]

  Yuji Omura

  日本物理学会秋季大会  2014/09
• Dark matter physics in 2HDMs  [Not invited]

  Yuji Omura

  Summer Institute 2014  2014/08
• Dark matter physics in 2HDMs  [Not invited]

  Yuji Omura

  基研研究会 素粒子物理学の進展 2014  2014/07
• Top FB asymmetry vs. (semi)leptonic B decays in multi-Higgs-Doublets Models  [Not invited]

  Yuji Omura

  SUSY2013  2013/08
• Gauged Leptophobic U(1)' models  [Not invited]

  Yuji Omura

  2013 International Workshop on Baryon and Lepton Number Violation (BLV2013) From the Cosmos to the LHC  2013/04
• Top FB asymmetry vs. (semi)leptonic B decays in multi-Higgs-Doublets Models  [Not invited]

  Yuji Omura

  Higgs as a Probe of New Physics 2013  2013/02
• Cold Dark Matters in U(1)' Models  [Invited]

  Yuji Omura

  Workshop on Dark Matter Phenomenology  2012/08
• Top A_FB at the Tevatron and charge asymmetry at the LHC in chiral U(1) flavor models with flavored Higgs doublets  [Not invited]

  Yuji Omura

  SUSY2012  2012/08
• Flavor Physics in Two-Higgs-Doublet Models with gauged U(1) flavor symmetry  [Invited]

  Yuji Omura

  APCTP 2012 LHC Physics Workshop at Korea  2012/08
• Top forward-backward asymmetry and charge asymmetry in chiral U(1) flavor models  [Not invited]

  Yuji Omura

  FLASY12 Workshop on Flavor Symmetries  2012/06
• Two Higgs Doublet Models with Higgs Flavor Symmetry  [Invited]

  Yuji Omura

  2011 Particle Physics Mini Workshop  2011/12
• Two Higgs Doublet Models with Higgs Flavor Symmetry  [Invited]

  Yuji Omura

  The 1st KIAS Phenomenology workshop  2011/11
• How can obtain neutrino mixing?  [Invited]

  Yuji Omura

  Theoretical Issues in Neutrino Physics  2011/11
• Dijet resonance and dark matters in leptophobic U(1)' models  [Invited]

  Yuji Omura

  Korea-CDF Collaboration Meeting  2011/05
• Dijet resonance and dark matters in leptophobic U(1)' models  [Invited]

  Yuji Omura

  TeV 2011  2011/05
• Supersymmetric U(1)_B times U(1)_L model with leptophilic and leptophobic cold dark matters  [Invited]

  Yuji Omura

  Joint Retreat on Cosmology and LHC Physics  2010/12
• Supersymmetric U(1)_B times U(1)_L model with leptophilic and leptophobic cold dark matters  [Invited]

  Yuji Omura

  LHC PHYSICS:W, Z AND BEYOND" 2010 topical program at NCTS in TAIWAN 2nd workshop  2010/12

MISC

• Interplay between the LHC and flavor physics

  Yuji Omura  Proceedings of The 4th KMI International Symposium — PoS(KMI2019)  2019/11
• Natural SUSY from unification of SUSY breaking and GUT breaking

  Yuji Omura  2015/04
• 23pDG-3 natural MSSM with nonuniversal gaugino masses at the LHC

  Abe Hiroyuki; Kawamura Junichiro; Omura Yuji  Meeting Abstracts of the Physical Society of Japan  70-  32  -32  2015
• 25aSD-3 non-universal gaugino massシナリオのLHC実験による検証

  安倍 博之; 川村 淳一郎; 大村 雄司  日本物理学会講演概要集  70-  3  -3  2015
• Two Higgs doublet models with local U(1)_H gauge symmetry and dark matter

  P. Ko; Yuji Omura; Chaehyun Yu  "proceedings of ""49th Rencontres de Moriond on QCD and High Energy Interactions"" pp.225-228"  2014/06
• Multi-Higgs doublet models with local U(1)(H) gauge symmetry and neutrino physics therein

  P. Ko; Yuji Omura; Chaehyun Yu  WORKSHOP ON DARK MATTER, NEUTRINO PHYSICS AND ASTROPHYSICS CETUP 2013: VIITH INTERNATIONAL CONFERENCE ON INTERCONNECTIONS BETWEEN PARTICLE PHYSICS AND COSMOLOGY PPC 2013  1604-  210  -219  2014
• Top FB asymmetry vs. (semi)leptonic B decays in multi-Higgs-doublet models

  P. Ko; Yuji Omura; Chaehyun Yu  2013/04
• Top Forward-backward asymmetry at the Tevatron vs. Charge asymmetry at the LHC in chiral U(1)' models with flavored Higgs fields

  P. Ko; Yuji Omura; Chaehyun Yu  HCP 2012 - HADRON COLLIDER PHYSICS SYMPOSIUM 2012  49-  2013
• Top A(FB) at the Tevatron vs. charge asymmetry at the LHC in chiral U(1) flavor models with flavored Higgs doublets

  P. Ko; Yuji Omura; Chaehyun Yu  EUROPEAN PHYSICAL JOURNAL C  73-  (1)  2013/01
• Top A_{FB} and charge asymmetry in flavor-dependent chiral U(1)' model

  P. Ko; Yuji Omura; Chaehyun Yu  2012/08
• Top forward-backward asymmetry in chiral U(1)' models

  P. Ko; Yuji Omura; Chaehyun Yu  Nuovo Cim. C035N3 (2012) 245-248  2012/01
• Cold Dark Matters in U(1)' Models

  Yuji Omura  7TH INTERNATIONAL WORKSHOP ON THE DARK SIDE OF THE UNIVERSE (DSU 2011)  384-  2012
• 30aVP-13 Soft supersymmetry breaking terms from A4 lepton flavor symmetry

  Ishimori Hajime; Kobayashi Tatsuo; Omura Yuji; Tanimoto Morimitsu  Meeting abstracts of the Physical Society of Japan  64-  (1)  18  -18  2009/03
• D4 flavor symmetry in SUSY

  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  -10  2008/02
• Metastable supersymmetry breaking vacua from conformal dynamics

  Yuji Omura  SUPERSYMMETRY AND THE UNIFICATION OF FUNDAMENTAL INTERACTIONS  1078-  465  -467  2008

Research Grants & Projects

• Study of vacuum structure based on the classification of dark matter models

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

  Date (from‐to) : 2019/04 -2023/03 

  Author : 大村 雄司

   

  本研究課題では、宇宙の真空構造と暗黒物質(DM)の解明を目的としている。特に(未知の)弱い相互作用をするDMに着目し、DMが他の素粒子とその相互作用を通して熱的に生成される模型を包括的に研究している。昨年度は、DMがレプトンと湯川相互作用をするレプトンポータルDM模型の研究をおこなった。ボトムアップ的に現象論的模型を構築し、DMの性質に基づいて模型の分類分けを行い、現在の実験バウンドと今後の展望を研究した。JHEP02(2021)231とJHEP08(2020)042にそれらの結果をまとめ、今年度はその研究成果を国内外の研究会で発表した。 この研究結果を踏まえ、今年度は宇宙の真空構造に関わる研究を行なった。我々の宇宙では、パリティ対称性とCP対称性が破れている。その一方で強いCP問題といった、CP対称性の破れが非常に小さいのはなぜか、という問題がある。そこで本研究課題では、パリティ対称性が我々の真空で自発的に破れている可能性を考え、その具体的な模型と特にフレーバー物理での検証方法や現在報告されている最新の実験結果との整合性を解析した。 JHEP06(2021)125 では、left-right 模型といったパリティ対称性を持つ模型でフレーバー物理での検証方法を研究した。そして、PRD104(2021)7,075008 では、Pati-Salam 模型といった右巻きと左巻きの粒子が湯川結合を除いて対称的になっている模型でフレーバー物理とコライダー物理を研究した。これらは上記のstrong CP 問題の解決策となりうることが過去に提案されている。今後、DM に関して得られた結果をもとに、パリティ対称性の自発的破れとDMとの関係を調べ、宇宙の真空構造とDMの関係を明らかにしていく。
• Investigation of the origin of the flavor structure based on new physics and dark matter searches

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2019/06 -2021/03 

  Author : 大村 雄司

   

  本研究では暗黒物質物理を含めた新物理探索実験に基づくフレーバー構造の起源の解明を目的とし研究を遂行している。素粒子のフレーバー構造には世代の謎や質量階層性の問題がある。さらには、フレーバーの入れ替えに対する対称性が高いエネルギーにいくと回復する可能性もある。これらのフレーバー構造の謎を解く新物理は数多く提案されている。例えばフレーバー対称性模型があるし、大統一理論のように部分的にフレーバー構造が統一される可能性も長年議論されている。これらはフレーバーを持つ余剰スカラーや余剰フェルミオンを予言し、フレーバー物理やその新粒子を直接観測する実験で検証が可能である。今年度は、それらのフレーバーを持つ余剰粒子のミューオンの異常磁気モーメント、暗黒物質物理への寄与を解析し、Belle2 実験やLHC実験での検証方法を研究した。 特に論文JHEP09(2020)144では宇宙の真空構造に関係するフレーバーを持つスカラー粒子のフレーバー物理への寄与を研究し、近年はじまったBelle2実験での画期的な検証方法を提案した。また、論文JHEP08(2020)042と JHEP02(2021)231では、フレーバーを持つ余剰スカラー粒子の物理だけでなく暗黒物質との関係も研究し、それらの新物理が将来実験で十分検証可能であることを数値的に示し、研究結果を物理学会と国際研究会で発表した。現在はこれらを踏まえて、フレーバー対称性を持つ模型や部分的にフレーバーを統一する具体的な模型で実際にフレーバー構造の起源を実験結果から解明できるかを研究している。
• Exploring for origin of neutrino masses using charged lepton flavor violation

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2019/04 -2021/03 

  Author : 大村 雄司

   

  本研究課題の目的は、荷電レプトンのフレーバーの破れ(cLFV) を伴う過程を用いたニュートリノの質量生成機構の検証を行うことである。ニュートリノ質量生成機構の代表例に、右巻きニュートリノを導入するType-Iシーソー機構とよばれるものがある。この機構は右巻きニュートリノが非常に重いために一般的には詳細な検証が非常に難しいことが予想される。しかし、大統一理論のような枠組みを想定するとcLFV の過程で質量機構の予言能力が残り、検証できるようになる。本研究では研究期間の２年かけて数値的にその予言を評価する計算コードを作成し、2021年3月に論文としてarXiv に発表した (arXiv:2103.12712)。また、暗黒物質の観測やミューオンの異常磁気モーメントの測定、LHCb実験で新しい結果が公表されている現状を踏まえて、それらの観測量でのニュートリノ質量生成機構を想定したときに現れる新物理の寄与を計算し、最新結果との整合性と将来実験での展望を研究した。これらの研究結果に関して論文JHEP08(2020)042で発表し、国際研究会においても研究結果を公表した。ニュートリノ実験やコライダー実験での検証方法も発見し、最近の論文JHEP02(2021)231で発表している。今後は、この結果をもとに輻射補正によるニュートリノ質量生成機構やInverse シーソー機構のcLFV による検証や暗黒物質との関係を研究していく。
• Investigation of dark matter and vacuum structure via flavor physics

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

  Date (from‐to) : 2017/04 -2019/03 

  Author : 大村 雄司

   

  宇宙の真空構造と暗黒物質(DM)の解明のため(未知の)弱い相互作用をする暗黒物質模型に焦点を絞り、DM の直接観測と間接観測、LHC 実験での新物理直接探索、フレーバー物理からのDM 模型の検証を行った。昨年度の研究を基に、単純化された暗黒物質模型((1)とする)と具体的な素粒子標準模型の問題点に基づいた模型((2)とする)を構築し、その中で暗黒物質に関する物理とフレーバー物理に特に焦点を置いて研究した。 (1)近年、LHCb実験やBファクトリー実験のフレーバー物理に関する観測量で素粒子標準模型からのズレが報告されている。そのズレに関して新物理の可能性を研究するだけでなく、背後に暗黒物質が存在する可能性を考え、論文(PRD96,no.7, 075041(2017), JHEP1902,194(2019))にまとめると共に、日本物理学会並びに国際研究会において、現在の進展状況を報告した。さらには物理学会誌の2019年3月号で最近のフレーバー物理に関する進展に関し報告した。 (2) 暗黒物質の可能性は数多く考えられている。その存在と素粒子標準模型の謎との関連を研究するため、具体的に問題点を改善する模型を構築し暗黒物質候補を探索した。具体的には、電弱相互作用のスケール起源とstrong CP問題を解決する超対称性LR模型を構築し、暗黒物質の候補を指摘し、レプトンのフレーバー物理による模型の検証方法を論(JHEP1811,046(2018))で提案した。近年では超対称性模型のない場合の模型の構築と暗黒物質の実現を研究しており、2019年3月の学会で結果を公表した。
• 超重力理論における超対称性の破れのダイナミクス、及びそれに伴う物理現象の研究

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2008 -2009 

  Author : 大村 雄司

   

  私は素粒子物理の理論分野において、超対称性模型における現象論及びTeVスケールにおける物理に関する研究を行っています。現在、それらの新しい物理を検証すべくLHC等の加速器実験、並びに宇宙観測が活発に行われており、それらの観測データから如何なる物理が考えうるかが、素粒子論の一つの課題となっています。 私は、本年度、4月から10月までイタリア(パドヴァ)、11月から3月まで韓国(KIAS)に滞在させていただき、研究活動を行ってきました。イタリアでは、積極的に研究会に参加させていただき、バレンシア大学(スペイン)、パドヴァ大学(イタリア)等で上記で挙げた研究内容を紹介させていただき、情報交換と貴重なアドバイスをいただくことができました。 韓国においても、私の研究課題である超対称性模型、及びQCD、Bphysics、余剰次元模型の研究が活発に行われており、情報交換と新たな発展に関する洞察、最新の実験データに対する示唆を十分に議論することができました。 具体的には、私の過去の研究であります、 "D(4)Flavor Symmetry for Neutrino Masses and Mixing." Hajime Ishimori, Tatsuo Kobayashi, Hiroshi Ohki, Yuji Omura, Ryo Takahashi, Morimitsu Tanimoto, Phys.Lett.B662 : 178-184, 2008,

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