Shinya Kanemura

We study new physics effects on the couplings of weak gauge bosons with the lightest CP-even Higgs boson ($h$), $hZZ$, and the trilinear coupling of the lightest Higgs boson, $hhh$, at the one-loop order, as predicted by the two Higgs doublet model. Those renormalized coupling constants can deviate from the standard model (SM) predictions due to two distinct origins: the tree level mixing effect of Higgs bosons and the quantum effect of additional particles in loop diagrams. The latter can be en

Even if new physics beyond the standard model indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC), and the LHC could find only the Higgs boson but nothing else. This is the so-called ``nightmare scenario.'' On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral weakly interacting massive particle

A phenomenological consequence of electroweak baryogenesis is studied in connection with the Higgs physics. In a two Higgs doublet model, the first-order phase transition can be strong enough to allow the electroweak baryogenesis due to the effect of extra Higgs bosons. We investigate the quantum correction to the triple coupling of the lightest Higgs boson in such a scenario, and find that the condition of the strong first-order phase transition necessarily leads to the deviation of at least 10

We propose a simple testable model with mass generation mechanisms for dark matter and neutrino based on the gauged $U(1{)}_{B\mathrm{\text{\ensuremath{-}}}L}$ symmetry and an exact ${Z}_{2}$ parity. The $U(1{)}_{B\mathrm{\text{\ensuremath{-}}}L}$ symmetry is spontaneously broken at the TeV scale, by which ${Z}_{2}$-odd right-handed neutrinos receive Majorana masses of the electroweak scale. The lightest one is a dark matter candidate, whose stability is guaranteed by the ${Z}_{2}$ parity. Resul

We investigate unitarity bounds in the most general two Higgs doublet model without a discrete Z2 symmetry nor CP conservation. S-wave amplitudes for two-body elastic scatterings of Nambu–Goldstone bosons and physical Higgs bosons are calculated at high energies for all possible initial and final states (14 neutral, 8 singly-charged and 3 doubly-charged states). We obtain analytic formulae for the block-diagonalized scattering matrix by the classification of the two body scattering states using

We study radiative corrections to the electroweak parameters in the Higgs model with the $Y=1$ triplet field, which is introduced in the scenario of generating neutrino masses based on the so-called type II seesaw mechanism. In this model, the rho parameter deviates from unity at the tree level. Consequently, the electroweak sector of the model is described by the four input parameters such as ${\ensuremath{\alpha}}_{\mathrm{em}}$, ${G}_{F}$, ${m}_{Z}$ and ${sin}^{2}{\ensuremath{\theta}}_{W}$.

We calculate radiative corrections to a full set of coupling constants for the 125 GeV Higgs boson at the one-loop level in two Higgs doublet models with four types of Yukawa interaction under the softly-broken discrete Z2 symmetry. The renormalization calculations are performed in the on-shell scheme, in which the gauge dependence in the mixing parameter which appears in the previous calculation is consistently avoided. We first show the details of our renormalization scheme, and present the co

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 ${Z}_{2}$ sym

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 t

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 $\mathrm{tan}\

We calculate renormalized Higgs boson couplings with gauge bosons and fermions at the one-loop level in the model with an additional isospin singlet real scalar field. These coupling constants can deviate from the predictions in the standard model due to tree-level mixing effects and one-loop contributions of the extra neutral scalar boson. We investigate how they can be significant under the theoretical constraints from perturbative unitarity and vacuum stability and also the condition of avoid

We investigate predictions on the triple Higgs boson couplings with radiative corrections in the model with an additional real singlet scalar field. In this model, the second physical scalar state (H) appears in addition to the Higgs boson (h) with the mass 125 GeV. The hhh vertex is calculated at the one-loop level, and its possible deviation from the predictions in the standard model is evaluated under various theoretical constraints. The decay rate of H→hh is also computed at the one-loop lev

We show a TeV-scale seesaw model where Majorana neutrino masses, the dark matter mass, and stability of the dark matter can be all originated from the $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$, and they are induced at the one-loop level by spontaneous $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ breaking. The right-handed neutrinos can be naturally at the TeV scale