1. |
Yuta Hamada, Kiyoharu Kawana, Koji Tsumura, Landau pole in the Standard Model with weakly interacting scalar fields, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2015.05.072, 747, 238-244, 2015.07, We consider the Standard Model with a new scalar field X which is an n_{X} representation of the SU(2)_{L} with a hypercharge Y_{X}. The renormalization group running effects on the new scalar quartic coupling constants are evaluated. Even if we set the scalar quartic coupling constants to be zero at the scale of the new scalar field, the coupling constants are induced by the one-loop effect of the weak gauge bosons. Once non-vanishing couplings are generated, the couplings rapidly increase by renormalization group effect of the quartic coupling constant itself. As a result, the Landau pole appears below Planck scale if n_{X}≥4. We find that the scale of the obtained Landau pole is much lower than that evaluated by solving the one-loop beta function of the gauge coupling constants.. |

2. |
Shinya Kanemura, Koji Tsumura, Kei Yagyu, Hiroshi Yokoya, Fingerprinting nonminimal Higgs sectors, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.90.075001, 90, 7, 2014.10, After the discovery of the standard model-like Higgs boson at the LHC, the structure of the Higgs sector remains unknown. We discuss how it can be determined by the combination of direct and indirect searches for additional Higgs bosons at future collider experiments. First of all, we evaluate expected excluded regions for the mass of additional neutral Higgs bosons from direct searches at the LHC with the 14 TeV collision energy in the two Higgs doublet models with a softly broken Z2 symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if the measured coupling constant with the gauge boson slightly deviates from the standard model value. In particular, in the two Higgs doublet model with the softly broken discrete symmetry, there are four types of Yukawa interactions, so that they can be discriminated by measuring the pattern of deviations in Yukawa coupling constants. Furthermore, we can fingerprint various extended Higgs sectors with future precision data by detecting the pattern of deviations in the coupling constants of the standard model-like Higgs boson. We demonstrate how the pattern of deviations can be different among various Higgs sectors that predict the electroweak rho parameter to be unity, such as models with additional an isospin singlet, a doublet, triplets, or a septet. We conclude that, as long as the gauge coupling constant of the Higgs boson slightly differs from the standard model prediction but is enough to be detected at the LHC and its high-luminosity run or at the International Linear Collider, we can identify the nonminimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.. |

3. |
Basudeb Dasgupta, Ernest Ma, Koji Tsumura, Weakly interacting massive particle dark matter and radiative neutrino mass from Peccei-Quinn symmetry, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.89.041702, 89, 4, 2014.02, The Peccei-Quinn anomalous global U(1)PQ symmetry is important for solving the strong CP problem with a cosmologically relevant axion. We add to this the simple (but hitherto unexplored) observation that it also has a residual Z2 symmetry which may be responsible for a second component of dark matter, i.e., an absolutely stable weakly interacting singlet scalar. This new insight provides a theoretical justification for this simplest of all possible dark-matter models. It also connects with the notion of generating radiative neutrino mass through dark matter. Two such specific realizations are proposed. In our general scenario, dark-matter detection is guaranteed at existing direct-detection experiments and/or axion searches. Observable signals at the Large Hadron Collider are discussed.. |

4. |
Junji Hisano, Koji Tsumura, Higgs boson mixes with an SU(2) septet representation, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.87.053004, 87, 5, 2013.03, We study the possibility of the Higgs boson, which consists of an SU(2) doublet and a septet. The vacuum expectation value of a septet with hypercharge Y=2 is known to preserve the electroweak rho parameter unity at the tree level. Therefore, the septet can give a significant contribution to the electroweak symmetry breaking. Because of the mixing with the septet, the gauge coupling of the standard-model-like Higgs boson is larger than that in the standard model. We show the sizable vacuum expectation value of the Higgs septet can be allowed under the constraint from the electroweak precision data. The signal strengths of the Higgs boson for the diphoton and a pair of weak gauge boson decay channels at the LHC are enhanced, while those for the fermionic decay modes are suppressed. The mass of additional neutral Higgs boson is also bounded by the current LHC data for the standard model Higgs boson. We discuss the phenomenology of the multiply charged Higgs bosons, which come from the septet.. |

5. |
Masaya Kohda, Hiroaki Sugiyama, Koji Tsumura, Lepton number violation at the LHC with leptoquark and diquark, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2012.12.048, 718, 4-5, 1436-1440, 2013.01, We investigate a model in which tiny neutrino masses are generated at the two-loop level by using scalar leptoquark and diquark multiplets. The diquark can be singly produced at the LHC, and it can decay into a pair of leptoquarks through the lepton number violating interaction. Subsequent decays of the two leptoquarks can provide a clear signature of the lepton number violation, namely two QCD jets and a pair of same-signed charged leptons without missing energy. We show that the signal process is not suppressed while neutrino masses are appropriately suppressed.. |

6. |
Hiroaki Sugiyama, Koji Tsumura, Hiroshi Yokoya, Discrimination of models including doubly charged scalar bosons by using tau lepton decay distributions, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2012.09.044, 717, 1-3, 229-234, 2012.10, The doubly charged scalar boson (H ^{±±}) is introduced in several models of the new physics beyond the standard model. The H ^{±±} has Yukawa interactions with two left-handed charged leptons or two right-handed charged leptons depending on the models. We study kinematical properties of H ^{±±} decay products through tau leptons in order to discriminate the chiral structures of the new Yukawa interaction. The chirality of tau leptons can be measured by the energy distributions of the tau decay products, and thus the chiral structure of the new Yukawa interaction can be traced in the invariant-mass distributions of the H ^{±±} decay products. We perform simulation studies for the typical decay patterns of the H ^{±±} with simple event selections and tau-tagging procedures, and show that the chiral structure of the Yukawa interactions of H ^{±±} can be distinguished by measuring the invariant-mass distributions.. |

7. |
Junji Hisano, Koji Tsumura, Masaki J.S. Yang, QCD corrections to neutron electric dipole moment from dimension-six four-quark operators, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2012.06.038, 713, 4-5, 473-480, 2012.07, In this Letter, the renormalization-group equations for the (flavor-conserving) CP-violating interaction are derived up to the dimension six, including all the four-quark operators, at one-loop level. We apply them to the models with the neutral scalar boson or the color-octet scalar boson which have CP-violating Yukawa interactions with quarks, and discuss the neutron electric dipole moment in these models.. |

8. |
Cheng Wei Chiang, Takaaki Nomura, Koji Tsumura, Search for doubly charged Higgs bosons using the same-sign diboson mode at the LHC, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.85.095023, 85, 9, 2012.05, Doubly charged Higgs bosons are predicted in many new physics models with an extended Higgs sector that contains a Higgs triplet field. Current experimental searches have been focusing mainly on the scenario in which the same-sign dilepton decay modes are the dominant ones. We study the scenario where the vacuum expectation value of the triplet field is sufficiently large so that the associated charged Higgs bosons decay dominantly to a pair of weak gauge bosons instead. A detailed simulation of the signal and the backgrounds is performed for the CERN Large Hadron Collider (LHC) at the collision energy of 8 TeV and 14 TeV. We find that different cuts should be imposed for the events, depending on whether the doubly charged Higgs boson mass is greater than about 200 GeV. In the higher mass region, the forward jet tagging proves to be useful in enhancing the signal significance. We show the discovery reach of the LHC running at 8 and 14 TeV, with two benchmark triplet vacuum expectation values. With an integrated luminosity of 10fb ^{-}1 at 8 TeV, the doubly charged Higgs boson with a mass of ∼180GeV can be tested at 5σ level in such a scenario.. |

9. |
Shinya Kanemura, Yasuhiro Okada, Hiroyuki Taniguchi, Koji Tsumura, Indirect bounds on heavy scalar masses of the two-Higgs-doublet model in light of recent Higgs boson searches, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2011.09.035, 704, 4, 303-307, 2011.10, We study an upper bound on masses of additional scalar bosons from the electroweak precision data and theoretical constraints such as perturbative unitarity and vacuum stability in the two-Higgs-doublet model taking account of recent Higgs boson search results. If the mass of the Standard-Model-like Higgs boson is rather heavy and is outside the allowed region by the electroweak precision data, such a discrepancy should be compensated by contributions from the additional scalar bosons. We show the upper bound on masses of the additional scalar bosons to be about 2 (1) TeV for the mass of the Standard-Model-like Higgs boson to be 240 (500) GeV.. |

10. |
Eri Asakawa, Daisuke Harada, Shinya Kanemura, Yasuhiro Okada, Koji Tsumura, Higgs boson pair production in new physics models at hadron, lepton, and photon colliders, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.82.115002, 82, 11, 2010.12, We study Higgs boson pair production processes at future hadron and lepton colliders including the photon collision option in several new physics models; i.e., the two-Higgs-doublet model, the scalar leptoquark model, the sequential fourth generation fermion model and the vectorlike quark model. Cross sections for these processes can deviate significantly from the standard model predictions due to the one-loop correction to the triple Higgs boson coupling constant. For the one-loop induced processes such as gg→hh and γγ→hh, where h is the (lightest) Higgs boson and g and γ respectively represent a gluon and a photon, the cross sections can also be affected by new physics particles via additional one-loop diagrams. In the two-Higgs-doublet model and scalar leptoquark models, cross sections of e ^{+}e^{-}→hhZ and γγ→hh can be enhanced due to the nondecoupling effect in the one-loop corrections to the triple Higgs boson coupling constant. In the sequential fourth generation fermion model, the cross section for gg→hh becomes very large because of the loop effect of the fermions. In the vectorlike quark model, effects are small because the theory has decoupling property. Measurements of the Higgs boson pair production processes can be useful to explore new physics through the determination of the Higgs potential.. |

11. |
Mayumi Aoki, Shinya Kanemura, Koji Tsumura, Kei Yagyu, Models of Yukawa interaction in the two Higgs doublet model, and their collider phenomenology, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.80.015017, 80, 1, 2009.08, Possible models of Yukawa interaction are discussed in the two Higgs doublet model (THDM) under the discrete symmetry imposed to avoid the flavor changing neutral current at the leading order. It is known that there are four types of such models corresponding to the possible different assignment of charges for the discrete symmetry on quarks and leptons. We first examine the decay properties of Higgs bosons in each type model, and summarize constraints on the models from current experimental data. We then shed light on the differences among these models in collider phenomenology. In particular, we mainly discuss the so-called type-II THDM and type-X THDM. The type-II THDM corresponds to the model with the same Yukawa interaction as the minimal supersymmetric standard model. On the other hand, in the type-X THDM, additional Higgs bosons can predominantly decay into leptons. This scenario may be interesting because of the motivation for a light charged Higgs boson scenario such as in the TeV-scale model of neutrinos, dark matter, and baryogenesis. We study how we can distinguish the type-X THDM from the minimal supersymmetric standard model at the Large Hadron Collider and the International Linear Collider.. |

12. |
Shinya Kanemura, Toshihiko Ota, Koji Tsumura, Lepton flavor violation in Higgs boson decays under the rare tau decay results, *Physical Review D - Particles, Fields, Gravitation and Cosmology*, 10.1103/PhysRevD.73.016006, 73, 1, 2006.01, We study lepton flavor violation (LFV) associated with tau leptons in the framework of the two Higgs doublet model, in which LFV couplings are introduced as a deviation from Model II Yukawa interaction. Parameters of the model are constrained from experimental results and also from requirements of theoretical consistencies such as vacuum stability and perturbative unitarity. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large tanβ region (tanβ30), which are comparable with predictions in fundamental theories. Here tanβ is the ratio of vacuum expectation values of the two Higgs doublets. We show that a search for the LFV decays 0→τ±μ (τ±e) of neutral Higgs bosons (0=h,H and A) at future collider experiments can be useful to further constrain the LFV couplings especially in the relatively small tanβ region (tanβ30), where rare tau decay data cannot give any strong limit.. |

13. |
Shinya Kanemura, Koichi Matsuda, Toshihiko Ota, Tetsuo Shindou, Eiichi Takasugi, Koji Tsumura, Search for lepton flavor violation in the Higgs boson decay at a linear collider, *Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics*, 10.1016/j.physletb.2004.08.024, 599, 1-2, 83-91, 2004.10, We discuss possibility of direct search for lepton flavor violation (LFV) in Yukawa interaction by measuring the branching ratio for the decay of the lightest Higgs boson (h ^{0}) into a τ-μ pair at a linear collider (LC). We study the significance of the signal process, e ^{+}e ^{-}→Z*→Zh ^{0}→Zτ ^{±}μ ^{∓}, against the backgrounds such as e ^{+}e ^{-}→Zτ ^{+}τ ^{-}→Zτ ^{±}μ ^{∓}+ missings. After taking appropriate kinematic cuts, the number of the background event is considerably reduced, so that the signal can be visible when the branching ratio of h ^{0}→τ ^{±}μ ^{∓} is larger than about 10 ^{-4}. In a minimal supersymmetric Standard Model scenario, the effective coupling of h ^{0}τ ^{±}μ ^{∓} can be generated at the loop level due to the slepton mixing. When supersymmetric mass parameters are larger than TeV scales, the branching ratio can be as large as several times 10 ^{-4}. Therefore, the signal can be marginally visible at a LC. In the general two-Higgs-doublet model, the possible maximal value for the branching ratio of h ^{0}→τ ^{±}μ ^{∓} can reach to a few times 10 ^{-3} within the available experimental bound, so that we can obtain larger significance.. |