研究者業績
基本情報
- 所属
- 千葉大学 大学院理学研究院物理学研究部門素粒子宇宙物理学講座 准教授名古屋大学 素粒子宇宙起源研究所 客員研究員
- 学位
- 博士（理学）(2015年3月 東京大学)
- 連絡先
- kitahara
chiba-u.jp - ORCID ID
https://orcid.org/0000-0002-4847-9511- J-GLOBAL ID
- 201701005824905218
- researchmap会員ID
- B000270613
- 外部リンク
経歴
8-
2024年2月 - 現在
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2023年8月 - 現在
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2023年6月 - 2024年2月
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2018年10月 - 2023年5月
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2022年4月 - 2023年3月
学歴
4-
2012年4月 - 2015年3月
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2010年4月 - 2012年3月
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2006年4月 - 2010年3月
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2003年4月 - 2006年3月
委員歴
3-
2024年12月 - 現在
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2023年5月 - 現在
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2021年10月 - 2024年1月
受賞
4-
2022年3月
論文
53-
Physical Review D 110(7) 2024年10月11日 査読有りThe measurements of the lepton flavor universality (LFU) in B(B¯→D(*)lν¯) indicate a significant deviation from the standard model prediction at a 3–4σ level, revealing a violation of the LFU (RD(*) anomaly). It is known that the RD(*) anomaly can be easily accommodated by an SU(2)L-singlet vector leptoquark (LQ) coupled primarily to third-generation fermions, whose existence is further motivated by a partial gauge unification. In general, such a LQ naturally leads to additional CP-violating phases in the LQ interactions. In this paper, we point out that the current RD(*) anomaly prefers the CP-violating interaction although B(B¯→D(*)lν¯) are CP-conserving observables. The CP-violating LQ predicts a substantial size of the bottom-quark electric dipole moment (EDM), the chromo-EDM, and also the tau-lepton EDM. Eventually at low energy, the nucleon and electron EDMs are radiatively induced. Therefore, we conclude that the RD(*) anomaly with the SU(2)L-singlet vector LQ provides unique predictions: neutron and proton EDMs with opposite signs and a magnitude of O(10−27) e cm, and suppressed electron EDM. Furthermore, we show that a similar EDM pattern is predicted in an SU(2)L-doublet scalar LQ scenario that can accommodate the RD(*) anomaly as well. These EDM signals could serve as crucial indicators in future experiments. Published by the American Physical Society 2024
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Physical Review D 110(7) 2024年10月9日 査読有りRecently, several new experimental results of the test of lepton flavor universality (LFU) in B→D(*) semileptonic decays were announced: the first result of RD from the LHCb run 1 data, the first results of RD and RD* from the LHCb run 2 data, and the first result of RD* from the Belle II collaboration. Including these new data, a global analysis still prefers the violation of the LFU between the tau and light leptons. A new world average of the data from the , LHCb, Belle, and Belle II collaborations is RD=0.342±0.026 and RD*=0.287±0.012. Including this new data, we update a circumstance of the b→cτν¯ measurements and their implications for new physics (NP). Incorporating recent developments for the B→D(*) form factors in the Standard Model, we observe a 4.4σ deviation from the Standard Model prediction. Our updates also include model-independent NP formulas for the related observables and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different NP scenarios with the use of the precise measurements of the polarization observables in B→D(*)τν¯ at the Belle II and the high-pT flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in ϒ→l+l−. Published by the American Physical Society 2024
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Journal of High Energy Physics 2024(2) 2024年2月26日 査読有りAbstract In this paper, we scrutinize a radiatively generated QCD θ parameter at the two-loop level based on both full analytical loop functions with the Fock-Schwinger gauge method and the effective field theory approach, using simplified models. We observe that the radiatively generated θ parameters at the low energy scale precisely match between them. It provides validity to perturbative loop calculations of the QCD θ parameter with the Fock-Schwinger gauge method. Furthermore, it is also shown that the ordinary Fujikawa method for the radiative θ parameter by using $$ \overline{\theta} $$ = −arg det $$ {\mathcal{M } }_q^{\textrm{loop } } $$ does not cover all contributions in the simplified models. But, we also find that when there is a scale hierarchy in CP-violating sector, evaluation of the Fujikawa method is numerically sufficient. As an application, we calculate the radiative θ parameter at the two-loop level in a slightly extended Nelson-Barr model, where the spontaneous CP violation occurs to solve the strong CP problem. It is found a part of the radiative θ parameters cannot be described by the Fujikawa method.
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Physical Review D 108(11) 2023年12月26日 査読有り
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Physical Review D 108(11) 2023年12月11日 査読有り
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Physical Review D 108(7) 2023年10月9日 査読有り
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Journal of High Energy Physics 2023(3) 2023年3月29日 査読有りAbstract There are two tensions related to the Cabibbo angle of the CKM matrix. First, the determinations of Vus from Kμ2, Kℓ3, and τ decays disagree at the 3σ level. Second, using the average of these results in combination with β decays (including super-allowed β decays and neutron decay), a deficit in first-row CKM unitarity with a significance of again about 3σ is found. These discrepancies, known as the Cabibbo Angle anomaly, can in principle be solved by modifications of W boson couplings to quarks. However, due to SU(2)L invariance, Z couplings to quarks are also modified and flavour changing neutral currents can occur. In order to consistently assess the agreement of a new physics hypothesis with data, we perform a combined analysis for all dimension-six Standard Model Effective Field Theory operators that generate modified W couplings to first and second generation quarks. We then study models with vector-like quarks, which are prime candidates for a corresponding UV completion as they can affect W -quark couplings at tree level, and we perform a global fit including flavour observables (in particular loop effects in ∆F = 2 processes). We find that the best fit can be obtained for the SU(2)L doublet vector-like quark Q as it can generate right-handed W-u-d and W-u-s couplings as preferred by data.
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Journal of High Energy Physics 2023(3) 2023年3月20日 査読有りAbstract When the QCD axion is absent in full theory, the strong CP problem has to be explained by an additional mechanism, e.g., the left-right symmetry. Even though tree-level QCD $$ \overline{\theta} $$ parameter is restricted by the mechanism, radiative corrections to $$ \overline{\theta} $$ are mostly generated, which leads to a dangerous neutron electric dipole moment (EDM). The ordinary method for calculating the radiative $$ \overline{\theta} $$ utilizes an equation $$ \overline{\theta}=-\arg\ \det {m}_q^{\textrm{loop } } $$ based on the chiral rotations of complex quark masses. In this paper, we point out that when full theory includes extra heavy quarks, the ordinary method is unsettled for the extra quark contributions and does not contain its full radiative corrections. We formulate a novel method to calculate the radiative corrections to $$ \overline{\theta} $$ through a direct loop-diagrammatic approach, which should be more robust than the ordinary one. As an application, we investigate the radiative $$ \overline{\theta} $$ in the minimal left-right symmetric model. We first confirm a seminal result that two-loop level radiative $$ \overline{\theta} $$ completely vanishes (corresponding to one-loop corrections to the quark mass matrices). Furthermore, we estimate the size of a non-vanishing radiative $$ \overline{\theta} $$ at three-loop level. It is found that the resultant induced neutron EDM is comparable to the current experimental bound, and the expected size is restricted by the perturbative unitarity bound in the minimal left-right model.
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Physical Review D 107(5) 2023年3月8日 査読有り
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Journal of High Energy Physics 2023(03) 2022年11月7日 査読有りWe find that the phase appearing in the unitarity relation between $\mathcal{B}(K_L\rightarrow \mu^+\mu^-)$ and $\mathcal{B}(K_L\rightarrow \gamma\gamma)$ is equal to the phase shift in the interference term of the time-dependent $K\rightarrow \mu^+\mu^-$ decay. A probe of this relation at future kaon facilities constitutes a Standard Model test with a theory precision of about $2\%$. The phase has further importance for sensitivity studies regarding the measurement of the time-dependent $K\rightarrow \mu^+\mu^-$ decay rate to extract the CKM matrix element combination $\vert V_{ts} V_{td} \sin(\beta+\beta_s)\vert\approx A^2\lambda^5\bar\eta$. We find a model-independent theoretically clean prediction, $\cos^2\varphi_0 = 0.96 \pm 0.03$. The quoted error is a combination of the theoretical and experimental errors, and both of them are expected to shrink in the future. Using input from the large-$N_C$ limit within chiral perturbation theory, we find a theory preference towards solutions with negative $\cos\varphi_0$, reducing a four-fold ambiguity in the angle $\varphi_0$ to a two-fold one.
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Physical Review D 107(7) 2022年10月31日 査読有りWe investigate the di-Higgs productions at the Large Hadron Collider in the two-Higgs doublet model. In particular, we study the productions of an extra scalar, $\phi$ ($\phi=H,\,A$), in association with the Standard Model (SM)-like Higgs boson, $h$. We consider a scenario that the additional scalars have a large top-Yukawa interaction in the Higgs alignment limit. Then, the leading contribution to the production comes from the loop-induced gluon-fusion channel $gg \to h\phi$. Similar to the SM Higgs pair production, these $h\phi$ productions are sensitive to the Higgs potential as well as the Yukawa couplings. In this paper, we calculate these $h\phi$ production cross sections at the leading order, taking into account the theoretical constraints from the perturbative unitarity and vacuum stability bounds as well as the precision measurements from the Higgs and flavor physics. Furthermore, we scrutinize the di-Higgs production in the parameter spaces that can explain the excesses around 100$\,$GeV in di-$\tau$ and di-photon and/or the muon $g-2$ anomaly.
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Reports on Progress in Physics 2022年10月24日 査読有りAbstract Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.
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Physical Review Letters 130(12) 2022年10月18日 査読有りFundamental physical constants are determined from a collection of precision measurements of elementary particles, atoms and molecules. This is usually done under the assumption of the Standard Model~(SM) of particle physics. Allowing for light new physics~(NP) beyond the SM modifies the extraction of fundamental physical constants. Consequently, setting NP bounds using these data, and at the same time assuming the CODATA recommended values for the fundamental physical constants, is not reliable. As we show in this Letter, both SM and NP parameters can be simultaneously determined in a consistent way from a global fit. For light vectors with QED-like couplings, such as the dark photon, we provide a prescription that recovers the degeneracy with the photon in the massless limit, and requires calculations only at leading order in the small new physics couplings. At present, the data show tensions partially related to the proton charge radius determination. We show that these can be alleviated by including contributions from a light scalar with flavor non-universal couplings.
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Journal of High Energy Physics 2022(11) 2022年8月1日 査読有りWe propose a four-dimensional interpretation of the outgoing state of the scattering of a massless fermion off a Dirac monopole. It has been known that such a state has fractional fermion numbers and is necessarily outside the Fock space on top of ordinary perturbative vacuum, when more than two flavours of charged Dirac fermions are considered. In this paper, we point out that the Fock space of the fermions depends on the rotor degree of freedom of the monopole and changes by a monopole-fermion s-wave scattering. By uplifting the fermion-rotor system introduced by Polchinski, from two to four dimensions, we argue that the outgoing state can be understood as a state in a different Fock space.
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European Physical Journal C 82(11) 2022年5月6日 査読有り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.
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Journal of High Energy Physics 2022(3) 2022年3月 査読有りAbstract We study the on-shell version of the Higgs mechanism in effective theories (EFTs) containing particles of different spins, focusing on contact terms as a simple starting point. We derive the massive contact terms and their coefficients from the massless amplitudes of the EFT above the symmetry breaking scale, by covariantizing the massless contact terms under the massive little group. In the little-group-covariant massive-spinor formalism, this notationally amounts to bolding spinor labels. Mass-suppressed contributions to the contact-term coefficients arise from higher-point contact terms with additional soft Higgs legs. We apply this procedure to obtain massive four-point amplitudes featuring scalars, spin 1/2 fermions and vectors, in the standard-model EFT. The subleading helicity-flipped components of each massive contact term, which are dictated by little-group covariance, are associated with the residues of factorizable massless amplitudes. Extra “frozen” Higgses emitted from each leg of a massless contact term supply the additional light-like momentum component, needed to form a massive leg of the same polarization. As another application, we derive various components of massive three-point amplitudes from massless amplitudes with up to three additional Higgses, in a standard-model-like toy model.
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Journal of High Energy Physics 2022(2) 2022年2月 査読有り<title>A<sc>bstract</sc> </title>Motivated by the <inline-formula><alternatives><tex-math>$$ b\to c\tau \overline{v} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>b</mml:mi> <mml:mo>→</mml:mo> <mml:mi>cτ</mml:mi> <mml:mover> <mml:mi>v</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></alternatives></inline-formula> anomalies, we study non-resonant searches for new physics at the large hadron collider (LHC) by considering final states with an energetic and hadronically decaying <italic>τ</italic> lepton, a <italic>b</italic>-jet and large missing transverse momentum <inline-formula><alternatives><tex-math>$$ \left( pp\to {\tau}_h\overline{b}+{E}_{\mathrm{T } }^{\mathrm{miss } }\right) $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mi>pp</mml:mi> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>τ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mover> <mml:mi>b</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>T</mml:mi> <mml:mtext>miss</mml:mtext> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math></alternatives></inline-formula>. Such searches can be useful to probe new physics contributions to <inline-formula><alternatives><tex-math>$$ b\to c\tau \overline{v} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>b</mml:mi> <mml:mo>→</mml:mo> <mml:mi>cτ</mml:mi> <mml:mover> <mml:mi>v</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></alternatives></inline-formula>. They are analyzed not only within the dimension-six effective field theory (EFT) but also in explicit leptoquark (LQ) models with the LQ non-decoupled. The former is realized by taking a limit of large LQ mass in the latter. It is clarified that the LHC sensitivity is sensitive to the LQ mass for 𝒪(1) TeV even in the search of <inline-formula><alternatives><tex-math>$$ pp\to {\tau}_h\overline{b}+{E}_{\mathrm{T } }^{\mathrm{miss } } $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>pp</mml:mi> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>τ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mover> <mml:mi>b</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>T</mml:mi> <mml:mtext>miss</mml:mtext> </mml:msubsup> </mml:math></alternatives></inline-formula>. Although the LQ models provide a weaker sensitivity than the EFT limit, it is found that the non-resonant search of <inline-formula><alternatives><tex-math>$$ pp\to {\tau}_h\overline{b}+{E}_{\mathrm{T } }^{\mathrm{miss } } $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>pp</mml:mi> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>τ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mover> <mml:mi>b</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>T</mml:mi> <mml:mtext>miss</mml:mtext> </mml:msubsup> </mml:math></alternatives></inline-formula> can improve the sensitivity by <italic>≈</italic> 40% versus a conventional mono-<italic>τ</italic> search <inline-formula><alternatives><tex-math>$$ \left( pp\to {\tau}_h+{E}_{\mathrm{T } }^{\mathrm{miss } }\right) $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mi>pp</mml:mi> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>τ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mi>E</mml:mi> <mml:mi>T</mml:mi> <mml:mtext>miss</mml:mtext> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math></alternatives></inline-formula> in the whole LQ mass region. Consequently, it is expected that most of the parameter regions suggested by the <inline-formula><alternatives><tex-math>$$ b\to c\tau \overline{v} $$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>b</mml:mi> <mml:mo>→</mml:mo> <mml:mi>cτ</mml:mi> <mml:mover> <mml:mi>v</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math></alternatives></inline-formula> anomalies can be probed at the HL-LHC. Also, it is shown that R2 LQ scenario is accessible entirely once the LHC Run 2 data are analyzed. In addition, we discuss a charge selection of <italic>τ</italic><italic>h</italic> to further suppress the standard-model background, and investigate the angular correlations among <italic>b</italic>, <italic>τ</italic> and the missing transverse momentum to discriminate the LQ scenarios.
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Journal of High Energy Physics 2021(7) 2021年7月 査読有りThe Fermilab Muon g− 2 collaboration recently announced the first result of measurement of the muon anomalous magnetic moment (g− 2), which confirmed the previous result at the Brookhaven National Laboratory and thus the discrepancy with its Standard Model prediction. We revisit low-scale supersymmetric models that are naturally capable to solve the muon g− 2 anomaly, focusing on two distinct scenarios: chargino-contribution dominated and pure-bino-contribution dominated scenarios. It is shown that the slepton pair-production searches have excluded broad parameter spaces for both two scenarios, but they are not closed yet. For the chargino-dominated scenario, the models with mμ˜L≳mχ˜1± are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low tan β with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with mμ˜ ≲ 230 GeV can explain the g− 2 anomaly while satisfying the LHC constraints. Furthermore, we checked that the stau-bino coannihilation works properly to realize the bino thermal relic dark matter. We also investigate heavy staus case for the bino-dominated scenario, where the parameter region that can explain the muon g− 2 anomaly is stretched to mμ˜ ≲ 1.3 TeV.
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Journal of Physics B: Atomic, Molecular and Optical Physics 54(8) 085502-085502 2021年4月21日 査読有り<title>Abstract</title> We propose a novel approach in a search for the neutron electric dipole moment (EDM) by taking advantage of signal amplification in a weak measurement, known as weak value amplification. Considering an analogy to the weak measurement that can measure the spin magnetic moment interaction, we examine an experimental setup with a polarized neutron beam through an external electric field with spatial gradient, where the signal is sensitive to the EDM interaction. In particular, a dedicated analysis of effects from impurities in pre- and post-selections is performed. We show that the weak value amplification occurs where the signal is enhanced by up to two orders of magnitude, and demonstrate a potential sensitivity of the proposed setup to the neutron EDM.
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Physical Review D Rapid Communication 2020年10月19日 査読有り
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Journal of High Energy Physics 2020(04) 165 2020年4月24日 査読有り
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Physical Review Letters 124(7) 2020年2月19日 査読有り
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2020年2月14日 査読有りRecently, it was pointed out that the electron and muon g-2 discrepancies can be explained simultaneously by a flavor-violating axion-like particle (ALP). We show that the parameter regions favored by the muon g-2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron g-2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment.
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Journal of High Energy Physics 2020(01) 119 2020年1月20日 査読有り
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CERN Yellow Reports: Monographs 2019(7) 867-1158 2019年12月3日 査読有り
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Physical Review D 100(3) 2019年8月28日 査読有り
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Journal of High Energy Physics 2019(07) 182 2019年7月31日 査読有り
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Physical Review D 99(7) 2019年4月 査読有り
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Journal of High Energy Physics 2019(2) 194 2019年2月 査読有り
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Physical Review Letters 120(26) 2018年6月 査読有り
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Journal of High Energy Physics 2018(4) 2018年4月1日 査読有りIn light of a discrepancy of the direct CP violation in K → ππ decays, ε′/εK , we investigate gluino contributions to the electroweak penguin, where flavor violations are induced by squark trilinear couplings. Top-Yukawa contributions to ΔS = 2 observables are taken into account, and vacuum stability conditions are evaluated in detail. It is found that this scenario can explain the discrepancy of ε′/εK for the squark mass smaller than 5.6 TeV. We also show that the gluino contributions can amplify ℬ (K→) , ℬ(KS → μ+μ−)eff and ΔACP(b → sγ). Such large effects could be measured in future experiments.
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PHYSICS LETTERS B 771 37-44 2017年8月 査読有りNew physics contributions to the Zpenguin are revisited in the light of the recently-reported discrepancy of the direct CP violation in K -> pi pi. Interference effects between the standard model and new physics contributions to Delta S= 2observables are taken into account. Although the effects are overlooked in the literature, they make experimental bounds significantly severer. It is shown that the new physics contributions must be tuned to enhance B(K-L -> pi(0) v (v) over bar), if the discrepancy of the direct CP violation is explained with satisfying the experimental constraints. The branching ratio can be as large as 6 x10(-10) when the contributions are tuned at the 10% level. (C) 2017 The Author(s). Published by Elsevier B.V.
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PHYSICAL REVIEW D 95(1) 2017年1月 査読有りThe observation of a protophobic 16.7 MeV vector boson has been reported by a Be-8 nuclear transition experiment. Such a new particle could mediate between the Standard Model and a dark sector, which includes the dark matter. In this paper, we show some simple models of the dark matter which satisfy the thermal relic abundance under the current experimental bounds from the direct and the indirect detections. In a model, it is found that an appropriate self-scattering cross section to solve the small scale structure puzzles can be achieved.
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Journal of High Energy Physics 2016(12) 2016年12月 査読有り
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Physical Review Letters 117(9) 2016年8月 査読有り
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JOURNAL OF HIGH ENERGY PHYSICS 2016(2) 2016年2月 査読有りMotivated by ATLAS diboson excess around 2TeV, we investigate a phenomenology of spin-1 resonances in a model where electroweak sector in the SM is weakly coupled to strong dynamics. The spin-1 resonances, W' and Z', are introduced as effective degrees of freedom of the dynamical sector. We explore several theoretical constraints by investigating the scalar potential of the model as well as the current bounds from the LHC and precision measurements. It is found that the main decay modes are V' -> VV and V' -> Vh, and the V' width is narrow enough so that the ATLAS diboson excess can be explained. In order to investigate future prospects, we also perform collider simulations at root s = 13 TeV LHC, and obtain a model independent expected exclusion limit for sigma(pp -> W' -> WZ -> JJ). We find a parameter space where the diboson excess can be explained, and are within a reach of the LHC at integral dt L = 10 fb(-1) and root s = 13 TeV.
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JOURNAL OF HIGH ENERGY PHYSICS 2016(1) 2016年1月 査読有りRecently the ATLAS experiment has reported 3.0 sigma excess in an on-Z signal region in searches for supersymmetric particles. We find that the next-to-minimal supersymmetric standard model can explain this excess by the production of gluinos which mainly decay via (g) over tilde -> g (chi) over tilde (0)(2,3) -> gZ (chi) over tilde (0)(1) where (chi) over tilde (0)(2,3) and (chi) over tilde (0)(1) are the Higgsino and the singlino-like neutralinos, respectively. We show that the observed dark matter density is explained by the thermal relic density of the singlino-like neutralino, simultaneously. We also discuss the searches for the Higgs sector of this scenario at the Large Hadron Collider.
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Physical Review D - Particles, Fields, Gravitation and Cosmology 91(7) 2015年4月27日 査読有りThe Bethe-Salpeter equation in the diquark channel is investigated by employing the Dyson-Schwinger method together with the Munczek-Nemirovsky model. The novelty of our study is a resummation of completely crossed ladder diagrams in the Bethe-Salpeter kernel. These diagrams are enhanced due to their color factors in the diquark channel, but not in the meson channel. In our analysis, diquark bound-state solutions exist in the Bethe-Salpeter equation.
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Physical Review D - Particles, Fields, Gravitation and Cosmology 91(5) 2015年3月4日 査読有りWe propose a new electroweak baryogenesis scenario in high-scale supersymmetric (SUSY) models. We consider a singlet extension of the minimal SUSY standard model introducing additional vectorlike multiplets. We show that the strongly first-order phase transition can occur at a high temperature comparable to the soft SUSY breaking scale. In addition, the proper amount of the baryon asymmetry of the Universe can be generated via the lepton number violating process in the vectorlike multiplet sector. The typical scale of our scenario, the soft SUSY breaking scale, can be any value. Thus our new electroweak baryogenesis scenario can be realized at arbitrary scales, and we call this scenario scale free electroweak baryogenesis. This soft SUSY breaking scale is determined by other requirements. If the soft SUSY breaking scale is O(10)TeV, our scenario is compatible with the observed mass of the Higgs boson and the constraints by electric dipole moment measurements and flavor experiments. Furthermore, the singlino can be a good candidate for dark matter.
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The University of Tokyo 2015年3月 査読有り
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Physical Review Letters 113(13) 2014年9月 査読有り
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JOURNAL OF HIGH ENERGY PHYSICS 2014(4) 2014年4月 査読有りWe study future prospects of the stau which contributes to the Higgs coupling to di-photon. The coupling is sensitive to new physics and planned to be measured at percent levels in future colliders. We show that, if the excess of the coupling is measured to be larger than 4%, the lightest stau is predicted to be lighter than about 200GeV by taking vacuum meta-stability conditions into account. Such a stau can be discovered at ILC. Moreover, we show how accurately the stau contribution to the coupling can be reconstructed from the information that is available at ILC. We also argue that, if the stau mixing angle is measured, the mass of the heaviest stau can be predicted by measuring the Higgs coupling, even when the heaviest stau is not yet discovered at the early stage of ILC.
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PHYSICS LETTERS B 728 274-281 2014年1月 査読有りWe study the possibility to determine the supersymmetric (SUSY) contribution to the muon anomalous magnetic dipole moment by using ILC measurements of the properties of superparticles. Assuming that the contribution is as large as the current discrepancy between the result of the Brookhaven E821 experiment and the standard-model prediction, we discuss how and how accurately the SUSY contribution can be reconstructed. We will show that, in a sample point, the reconstruction can be performed with the accuracy of similar to 13% with the center-of-mass energy 500 GeV and the integrated luminosity similar to 500-1000 fb(-1). (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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JOURNAL OF HIGH ENERGY PHYSICS 2014(1) 2014年1月 査読有りWe calculate all gauge invariant Barr-Zee type contributions to fermionic electric dipole moments (EDMs) in the two-Higgs doublet models (2HDM) with softly broken Z(2) symmetry. We start by studying the tensor structure of h -> VV' part in the Barr-Zee diagrams, and we calculate the effective couplings in a gauge invariant way by using the pinch technique. Then we calculate all Barr-Zee diagrams relevant for electron and neutron EDMs. We make bounds on the parameter space in type-I, type-II, type-X, and type-Y 2HDMs. The electron and neutron EDMs are complementary to each other in discrimination of the 2HDMs. Type-II and type-X 2HDMs are strongly constrained by recent ACME experiment's result, and future experiments of electron and neutron EDMs may search O(10) TeV physics.
MISC
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International Journal of Modern Physics A 39(26n27) 2024年8月24日 査読有りIn this paper, we present the current situation of the determinations of the first-row CKM components and show the Cabibbo angle anomaly corresponding to a deficit in the first-row CKM unitarity condition at the [Formula: see text] level. In this contribution, we show two new physics interpretations: heavy vector-like quark models and a MeV scale sterile neutrino scenario. The super tau-charm facility will directly probe the other CKM unitarity conditions related to [Formula: see text].
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Journal of Physics: Conference Series 2446(1) 012009-012009 2023年2月1日 査読有りAbstract Based on recent developments in the lattice simulations and calculations of the radiative corrections to the charged-current interactions, the uncertainties for each component in the CKM matrix have been sophisticated. It is known that the first-row CKM unitarity is violated at about 3σ level, implying a 3σ level deviation from the standard model prediction. This new deviation is called Cabibbo-Angle Anomaly (CAA). These CKM components are mainly extracted from kaon, pion, and the superallowed beta decays. In this contribution, we point out that a MeV scale sterile neutrino can economically explain the CAA. We consistently investigate the sterile neutrino contributions to the kaon, pion, superallowed beta decays, and also the Fermi coupling constant.
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2022年10月19日Recently, the LHCb collaboration announced a preliminary result of the test of lepton flavor universality (LFU) in $B\to D^{(\ast)}$ semi-leptonic decays: $R_{D}^{\rm LHCb2022} = 0.441 \pm 0.089$ and $R_{D^{\ast } }^{\rm LHCb2022} = 0.281 \pm 0.030$ based on the LHC Run\,1 data. This is the first result of $R_{D}$ for the LHCb experiment, and its precision is comparable to the other $B$-factory data. Interestingly, those data prefer the violation of the LFU again. Including this new result, we update a circumstance of the $b \to c \tau \bar\nu$ measurements and their implications for new physics. A new wold average of the data by the BaBar, Belle, and LHCb collaborations is $R_{D} = 0.358 \pm 0.028$ and $R_{D^{\ast } } = 0.285 \pm 0.013$. Incorporating several recent developments of determinations of the $B \to D^{(\ast)}$ form factors in the Standard Model (SM), we observe a $4.1 \sigma$ deviation from the SM predictions. The general new physics formulae and the global fittings of the new physics parameters are also updated. Furthermore, precise measurements of the polarization observables in the $B\to D^{(\ast)}$ semi-leptonic decays at the Belle~II experiment, and the high-$p_{\rm T}$ flavored-tail searches at the LHC experiment will be able to indirectly distinguish different new physics models. We also discuss the LFU violation in $\Upsilon \to l^+ l^-$.
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2022年9月27日This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.
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2022年9月21日The wealth of experimental data collected at laboratory experiments suggests that there is some scale separation between the Standard Model (SM) and phenomena beyond the SM (BSM). New phenomena can manifest itself as small corrections to SM predictions, or as signals in processes where the SM predictions vanish or are exceedingly small. This makes precise calculations of the SM expectations essential, in order to maximize the sensitivity of current and forthcoming experiments to BSM physics. This topical group report highlights some past and forthcoming theory developments critical for maximizing the sensitivity of the experimental program to understanding Nature at the shortest distances.
書籍等出版物
3講演・口頭発表等
91担当経験のある科目(授業)
8共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2024年7月 - 2026年3月
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日本学術振興会 科学研究費助成事業 若手研究 2019年4月 - 2023年3月
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Pursuit of CP-violating physics beyond the Standard Model through precision flavor physics (decline)National Natural Science Foundation of China National Natural Science Fund
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The Lady Davis Foundation
学術貢献活動
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企画立案・運営等University of Santiago de Compostela 2023年9月
社会貢献活動
2メディア報道
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KIT, Elementary Particle and Astroparticle Physics Center (KCETA) News 2024年1月 インターネットメディア