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Gravitational waves as a probe of extended scalar sectors with the first order electroweak phase transitionSep 28 2015Dec 13 2015We discuss spectra of gravitational waves which are originated by the strongly first order phase transition at the electroweak symmetry breaking, which is required for a successful scenario of electroweak baryogenesis. Such spectra are numerically evaluated ... More

Loop Suppression of Dirac Neutrino Mass in the Neutrinophilic Two Higgs Doublet ModelMay 20 2013Nov 10 2013We extend the scalar sector of the neutrinophilic two Higgs doublet model, where small masses of Dirac neutrinos are obtained via a small vacuum expectation value v_nu of the neutrinophilic SU(2)_L-doublet scalar field which has a Yukawa interaction with ... More

Novel Enhancement of Loop-Induced $H^\pm W^\mp Z^0$ VertexDec 19 1997We discuss the non-decoupling effects on the loop-induced $H^\pm W^\mp Z^0$ vertex in the general two Higgs-doublet model. The decay process $H^\pm \to W^\pm Z^0$ is analyzed at one-loop level and possible enhancement of the decay width is explored. We ... More

Gravitational waves from first order electroweak phase transition in models with the $U(1)_X^{}$ gauge symmetryFeb 08 2018We consider a standard model extension equipped with a dark sector where the $U(1)_X^{}$ Abelian gauge symmetry is spontaneously broken by the dark Higgs mechanism. In this framework, we investigate patterns of the electroweak phase transition as well ... More

Summary Report for Electroweak Symmetry Breaking Session in LCWS 2004Oct 08 2004Theoretical activities on the Higgs physics and its implication to physics beyond the standard model are summarized as the summary report for the Higgs session in LCWS 2004.

Synergy between measurements of the gravitational wave and the triple Higgs coupling in probing first order phase transitionApr 07 2016Jul 20 2016Probing the Higgs potential and new physics behind the electroweak symmetry breaking is one of the most important issues of particle physics. In particular, nature of electroweak phase transition is essential for understanding physics at the early Universe, ... More

Possible enhancement of the $e^+ e^- \to H^\pm W^\mp$ cross section in the two-Higgs-doublet modelNov 30 1999Jul 09 2000The production process of the charged Higgs-boson associated with a $W$ boson at electron-positron colliders is discussed in the two-Higgs-Doublet Model (2HDM) and in the Minimal Supersymmetric Standard Model (MSSM). The process is induced at one-loop ... More

Higgs Physics as a Proble of New PhysicsFeb 26 2014The discovery of the Higgs boson at the LHC has opened the door to clarify the mechanism of electroweak symmetry breaking and the origin of masses of particles. The Higgs sector in the SM is the simplest but has no theoretical principle, so that there ... More

Enhancement of Loop Induced $H^\pm W^\mp Z^0$ Vertex in Two Higgs-doublet ModelOct 03 1997Oct 06 1997The non-decoupling effects of heavy Higgs bosons as well as fermions on the loop-induced $H^\pm W^\mp Z^0$ vertex are discussed in the general two Higgs doublet model. The decay width of the process $H^+ \to W^+ Z^0$ is calculated at one-loop level and ... More

Unitarity bound in the most general two Higgs doublet modelSep 20 2015Dec 01 2015We investigate unitarity bounds in the most general two Higgs doublet model without a discrete $Z_2$ symmetry nor CP conservation. S-wave amplitudes for two-body elastic scatterings of Nambu-Goldstone bosons and physical Higgs bosons are calculated at ... More

Thermodynamics in 2+1 Dimensional QED with Chern-Simons TermMay 24 1995May 25 1995It is known that in the 2+1 dimensional quantum electrodynamics with Chern-Simons term, spontaneous magnetic field induces Lorentz symmetry breaking. In this paper, thermodynamical characters, especially the phase structure of this model are discussed. ... More

Probing the Majorana nature of TeV-scale radiative seesaw models at the ILCJul 05 2010Two important features of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated at the quantum level, are an extended scalar (Higgs) sector and the Majorana nature. We study phenomenological aspects of these models at the ILC. ... More

The $H^\pm W^\mp Z^0$ vertex and single charged Higgs boson production via $WZ$ fusion at the Large Hadron ColliderJun 29 2005Jul 05 2005There is a variety of new physics scenarios which deduce extended Higgs sectors in the low energy effective theory. The coupling of a singly-charged Higgs boson ($H^\pm$) with weak gauge bosons, $H^\pm W^\mp Z^0$, directly depends on the global symmetry ... More

Effects of the anomalous Higgs couplings on the Higgs boson production at the Large Hadron ColliderOct 02 2008Aug 02 2009We study the impact of dimension-six operators on single- and double-Higgs production rates via gluon fusion at the Large Hadron Collider (LHC). If the top-Yukawa coupling is modified by some new physics whose scale is of the TeV scale, its effect changes ... More

Radiative corrections to electroweak parameters in the Higgs triplet model and implication with the recent Higgs boson searchesJan 30 2012Jun 06 2012We 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 ... More

Thermodynamic properties of spontaneous magnetization in Chern-Simons QED_3Nov 22 1996The spontaneous magnetization in Chern-Simons QED_3 is discussed in a finite temperature system. The thermodynamical potential is analyzed within the weak field approximation and in the fermion massless limit. We find that there is a linear term with ... More

Probing Models of Neutrino Masses via the Flavor Structure of the Mass MatrixOct 29 2015Dec 01 2015We discuss what kinds of combinations of Yukawa interactions can generate the Majorana neutrino mass matrix. We concentrate on the flavor structure of the neutrino mass matrix because it does not depend on details of the models except for Yukawa interactions ... More

Unitarity bounds in the Higgs model including triplet fields with custodial symmetryDec 25 2007Apr 09 2008We study bounds on Higgs boson masses from perturbative unitarity in the Georgi-Machacek model, whose Higgs sector is composed of a scalar isospin doublet, a real and a complex isospin triplet fields. This model can be compatible with the electroweak ... More

A powerful tool for measuring Higgs boson associated Lepton Flavour ViolationJan 20 2009Apr 08 2009In models with extended Higgs sectors, Higgs-boson-mediated Lepton Flavour Violation (LFV) can naturally appear. We study the physics potential of an electron-photon collider %as an option of the International Linear Collider on searching LFV processes ... More

Neutrino Masses from Loop-induced $d \geq 7$ OperatorsSep 20 2010We propose a new scenario where neutrino masses are generated via operators with the mass dimension higher than five, which are induced at the loop level. The scenario is demonstrated with concrete models where neutrino masses are generated via a one-loop ... More

Probing the Majorana nature of TeV-scale radiative seesaw models at collider experimentsDec 31 2009Jun 09 2010A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale ... More

New mechanism for the top-bottom mass hierarchyFeb 28 2004Jul 23 2004We propose a mechanism to generate hierarchy between masses of the top and bottom quarks without fine tuning of the Yukawa coupling constants in the context of the two Higgs doublet model (THDM). In the THDM with a discrete symmetry, there exists the ... More

A Mechanism for the Top-Bottom Mass HierarchyAug 27 2004We discuss a mechanism to generate hierarchy between masses of the top and bottom quarks without fine-tuning of the Yukawa coupling constants. In the framework of the two-Higgs-doublet model (THDM) with a discrete $Z_2$ symmetry, there exists the vacuum ... More

Radiative Corrections to the Higgs Boson Decay into a Longitudinal $W$-Boson Pair in a Two-Doublet ModelOct 13 1994The decay rate of a (neutral) Higgs boson ($H$) going into a longitudinal $W$-boson pair is calculated by including one loop radiative corrections in a two-Higgs doublet model. It is assumed that the Higgs boson $H$ is much heavier than the $W$ boson ... More

Observing the Coupling between Dark Matter and Higgs Boson at the ILCJun 28 2010One of the main purposes on physics at the International Linear Collider (ILC) is to study the property of dark matter such as its mass, spin, and interactions between the dark matter and particles in the standard model. Among those, the interaction between ... More

Can the charged Higgs boson be discovered in $eγ$ collisions using the channel $e^-γ\toνH^-$?Apr 18 2001We consider the single production of charged Higgs bosons $H^\pm$ of the two-Higgs-doublet model in $e\gamma$ collisions through the production subprocess $e^-\gamma\to\nu H^-$. As the production rate is governed by the size of the loop-induced $H^\pm ... More

Dark matter and a suppression mechanism for neutrino masses in the Higgs triplet modelFeb 23 2012Mar 20 2012We extend the Higgs triplet model so as to include dark matter candidates and a simple suppression mechanism for the vacuum expectation value (v_Delta) of the triplet scalar field. The smallness of neutrino masses can be naturally explained with the suppressed ... More

Measuring Higgs boson associated Lepton Flavour Violation in electron-photon collisions at the ILCAug 06 2010Oct 18 2010We study the LFV Higgs production processes $e^-\gamma\to\ell^-\phi\;(\ell=\mu,\tau; \phi=H, A)$ as a probe of Higgs mediated LFV couplings at an electron-photon collider, where $H$ and $A$ are extra CP even and odd Higgs bosons, respectively, in the ... More

Testing Supersymmetry in the Associated Production of CP-odd and Charged Higgs BosonsDec 12 2001In the Minimal Supersymmetric Standard Model (MSSM), the masses of the charged Higgs boson ($H^\pm$) and the CP-odd scalar ($A$) are related by $M_{H^+}^2=M_A^2+m_W^2$. Furthermore, because the coupling of $W^-$-$A$-$H^+$ is fixed by gauge interaction, ... More

Non-Decoupling Effects of Higgs Bosons on $e^+e^- \to W^+_LW^-_L$ in the Two-Doublet ModelJul 24 1997Oct 06 1997The non-decoupling effects of heavy Higgs bosons on the process $e^+e^- \to W^+_LW^-_L$ are discussed in the two Higgs-doublet model. The one-loop corrections to the cross section are calculated by using the equivalence theorem and the explicit expressions ... More

Radiative neutrino mass, dark matter and electroweak baryogenesis from the supersymmetric gauge theory with confinementMay 22 2014We propose a simple model to explain neutrino mass, dark matter and baryogenesis based on the extended Higgs sector which appears in the low-energy effective theory of a supersymmetric gauge theory with confinement. We here consider the SU(2)$_H$ gauge ... More

Fingerprinting the extended Higgs sector using one-loop corrected Higgs boson couplings and future precision measurementsFeb 26 2015Apr 17 2015We 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 $Z_2$ symmetry. The renormalization ... More

An extended Higgs sector for neutrino mass, dark matter and baryon asymmetryFeb 18 2009In this talk, we discuss a TeV scale model which would explain neutrino oscillation, dark matter, and baryon asymmetry of the Universe simultaneously by the dynamics of the extended Higgs sector and TeV-scale right-handed neutrinos. By the imposed exact ... More

Enhancement of W+/- H-/+ Production at Hadron Colliders in the Two Higgs Doublet ModelJun 24 2005We discuss the associated W+/- H-/+ production at the CERN Large Hadron Collider. The dependence of the hadronic cross section on the Higgs sector parameters is investigated in detail in the framework of the general Two Higgs Doublet Model (THDM). We ... More

Phenomenology of the Georgi-Machacek model at future electron-positron collidersOct 21 2015Mar 14 2016We study the phenomenology of the exotic Higgs bosons in the Georgi-Machacek model at future electron-positron colliders such as the International Linear Collider (ILC), assuming the collision energies of 500 GeV and 1 TeV. We show that the existence ... More

Beam Dump Experiment at Future Electron-Positron CollidersJul 10 2015We propose a new beam dump experiment at future colliders with electron ($e^-$) and positron ($e^+$) beams, BDee, which will provide a new possibility to search for hidden particles, like hidden photon. If a particle detector is installed behind the beam ... More

Single production of charged Higgs bosons at linear collidersJan 31 2001We discuss single charged Higgs boson production from $e^+e^-$ annihilation at next generation linear colliders. They can be important to study the phenomenology of charged Higgs bosons, especially when charged Higgs bosons are too heavy to be produced ... More

Discriminative phenomenological features of scale invariant models for electroweak symmetry breakingAug 13 2015Aug 19 2015Classical scale invariance (CSI) may be one of the solutions for the hierarchy problem. Realistic models for electroweak symmetry breaking based on CSI require extended scalar sectors without mass terms, and the electroweak symmetry is broken dynamically ... More

A TeV scale model for neutrino mass, dark matter and baryon asymmetryMay 25 2009We discuss a TeV scale model which would explain neutrino oscillation, dark matter, and baryon asymmetry of the Universe simultaneously by the dynamics of the extended Higgs sector and TeV-scale right-handed neutrinos with imposed an exact $Z_2$ symmetry. ... More

TeV-Scale Seesaw with Loop-Induced Dirac Mass Term and Dark Matter from U(1)_{B-L} Gauge Symmetry BreakingNov 02 2011Jan 02 2012We 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)_{B-L} gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by U(1)_{B-L}, ... More

Neutrino Masses from Loop-Induced Dirac Yukawa CouplingsJun 13 2011We consider a possibility to naturally explain tiny neutrino masses without the lepton number violation. We study a simple model with SU(2)_L singlet charged scalars (s_1^+, s_2^+) as well as singlet right-handed neutrino (nu_R). Yukawa interactions for ... More

One-loop contributions of the super-partner particles to $e^-e^+ \to W^-W^+$ in the MSSMSep 17 2000One-loop contributions of super-partner particles to $W$-pair production at $e^+e^-$ collision are discussed in the MSSM. To obtain trustworthy results we test our calculation using three methods: (1) sum rules among form factors which result from the ... More

Electroweak baryogenesis and the triple Higgs boson couplingJul 22 2005Jul 23 2005We study collider signatures of electroweak baryogenesis in the two Higgs doublet model and the minimal supersymmetric standard model. It is found that the trilinear coupling of the lightest Higgs boson receives large quantum corrections if the electroweak ... More

Thermodynamic Gross-Neveu model under constant electromagnetic fieldJul 09 1997Dec 24 1997Analyzed is the effective potential of D-dimensional thermodynamic Gross-Neveu model (defined by large-N leading order, $2\leq D<4$) under constant electromagnetic field ($\vec{E}\cdot\vec{B}=0$). The potential is derived from a thermal analogy of the ... More

Higgs inflation in a radiative seesaw modelNov 19 2012Apr 13 2013We investigate a simple model to explain inflation, neutrino masses and dark matter simultaneously. This is based on the so-called radiative seesaw model proposed by Ma in order to explain neutrino masses and dark matter by introducing a $Z_2$-odd isospin ... More

Neutrino Mass and Dark Matter from Gauged $U(1)_{B-L}$ BreakingMay 08 2014Jul 09 2014We propose a new model where the Dirac mass term for neutrinos, the Majorana mass term for right-handed neutrinos, and the other new fermion masses arise via the spontaneous breakdown of the $U(1)_{B-L}$ gauge symmetry. The anomaly-free condition gives ... More

First-order electroweak phase transition powered by additional F-term loop effects in an extended supersymmetric Higgs sectorSep 24 2011Oct 20 2011We investigate the one-loop effect of new charged scalar bosons on the Higgs potential at finite temperatures in the supersymmetric standard model with four Higgs doublet chiral superfields as well as a pair of charged singlet chiral superfields. In this ... More

Masses of dark matter and neutrino from TeV scale spontaneous $U(1)_{B-L}$ breakingJan 29 2011Jul 27 2011We propose a simple testable model with mass generation mechanisms for dark matter and neutrino based on the gauged $U(1)_{B-L}$ symmetry and an exact $Z_2$ parity. The $U(1)_{B-L}$ symmetry is spontaneously broken at the TeV scale, by which $Z_2$-odd ... More

ILC phenomenology in a TeV scale radiative seesaw model for neutrino mass, dark matter and baryon asymmetryAug 14 2010We discuss phenomenology in a new TeV scale model which would explain neutrino oscillation, dark matter, and baryon asymmetry of the Universe simultaneously by the dynamics of the extended Higgs sector and TeV-scale right-handed neutrinos. Tiny neutrino ... More

R-Parity Conserving Supersymmetric Extension of the Zee ModelAug 23 2015Dec 09 2015We extend the Zee model, where tiny neutrino masses are generated at the one loop level, to a supersymmetric model with R-parity conservation. It is found that the neutrino mass matrix can be consistent with the neutrino oscillation data thanks to the ... More

Radiative type-I seesaw model with dark matter via U(1)_{B-L} gauge symmetry breaking at future linear collidersJul 30 2012We discuss phenomenology of the radiative seesaw model in which spontaneous breaking of the U(1)$_{B-L}$ gauge symmetry at the TeV scale gives the common origin for masses of neutrinos and dark matter (Kanemura et al., 2012). In this model, the stability ... More

Searches for additional Higgs bosons in multi-top-quarks events at the LHC and the International Linear ColliderMay 05 2015We study direct searches of additional Higgs bosons in multi-top-quarks events at the LHC Run-II, its luminosity upgraded version with 3000 fb$^{-1}$, and the International Linear Collider (ILC) with the collision energy of 1 TeV. Additional Higgs bosons ... More

First constraint on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario at the LHCMay 10 2013Jul 05 2013When the doubly-charged Higgs bosons $H^{\pm\pm}$ mainly decay into the same-sign dilepton, a lower bound on the mass is around 400 GeV by the current LHC data. On the other hand, no such bound has been reported by using the data at LEP and at the LHC ... More

The MSSM prediction for W+/- H-/+ production by gluon fusionAug 29 2000Jan 22 2001We discuss the associated W+/- H-/+ production in p p collision for the Large Hadron Collider. A complete one-loop calculation of the loop-induced subprocess g g -> W+/- H-/+ is presented in the framework of the Minimal Supersymmetric Standard Model (MSSM), ... More

Multi-tau-lepton signatures at the LHC in the two Higgs doublet modelNov 25 2011A detailed simulation study is performed for multi-tau-lepton signatures at the Large Hadron Collider, which can be used to probe additional Higgs bosons with lepton-specific Yukawa interactions. Such an extended Higgs sector is introduced in some of ... More

Testing Higgs models via the $H^\pm W^\mp Z$ vertex by a recoil method at the International Linear ColliderMar 02 2011In general, charged Higgs bosons $H^\pm$ appear in non-minimal Higgs models. The $H^\pm W^\mp Z$ vertex is known to be related to the violation of the global symmetry (custodial symmetry) in the Higgs sector. Its magnitude strongly depends on the structure ... More

Non-decoupling effects in supersymmetric Higgs sectorsSep 09 2010Apr 20 2011A wide class of Higgs sectors is investigated in supersymmetric standard models. When the lightest Higgs boson (h) looks the standard model one, the mass (m_h) and the triple Higgs boson coupling (the hhh coupling) are evaluated at the one-loop level ... More

Decoupling Property of SUSY Extended Higgs Sectors and Implication for Electroweak BaryogenesisMar 02 2012One-loop contributions to the Higgs potential at finite temperatures are discussed in the supersymmetric standard model with four Higgs doublet chiral superfields as well as a pair of charged singlet chiral superfields. The mass of the lightest Higgs ... More

Gluon jet as a probe of a long-lived colored particle at the LHCOct 09 2009Feb 20 2010In some new physics models, there exists a long-lived colored particle. Although such a particle is expected be discovered by studying the muon-like tracks, it is not easy to discriminate hadronic events from leptonic ones at the Large Hadron Collider. ... More

Radiative corrections to the Yukawa coupling constants in two Higgs doublet modelsJan 02 2014Feb 21 2014We calculate one-loop corrected Yukawa coupling constants $hf\bar{f}$ for the standard model like Higgs boson $h$ in two Higgs doublet models. We focus on the models with the softly-broken $Z_2$ symmetry, which is imposed to avoid the flavor changing ... More

One-loop contributions of charginos and neutralinos to W+ W- production in e+ e- collisionsFeb 10 2004We study one-loop effects of charginos and neutralinos on the helicity amplitudes for the process $e^+e^-\to W^+W^-$ in the MSSM. The calculation is tested by using two methods. First, the sum rules among form factors which result from BRS invariance. ... More

Reconstruction of Inert Doublet Scalars at the International Linear ColliderMar 25 2013Aug 19 2013We study collider signatures for extra scalar bosons in the inert doublet model at the international linear collider (ILC). The inert doublet model is a simple extension of the standard model by introducing an additional isospin-doublet scalar field which ... More

Multi-Higgs portal dark matter under the CDMS II resultsDec 30 2009Feb 08 2010In a scenario of Higgs portal dark matter, Higgs exchange processes are essential for both dark matter annihilation in the early Universe and direct search experiments. The CDMS II collaboration has recently released their final results on direct dark ... More

A Model of TeV Scale Physics for Neutrino Mass, Dark Matter and Baryon Asymmetry and its PhenomenologyApr 24 2009Aug 16 2009We discuss some details for the model proposed in Ref. \cite{aks-prl}, in which neutrino oscillation, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by the TeV-scale physics without introducing very high mass scales. ... More

A light Higgs scenario based on the TeV-scale supersymmetric strong dynamicsJun 05 2012Sep 02 2012We consider a model based on the supersymmetric QCD theory with N_c=2 and N_f=3. The theory is strongly coupled at the infrared scale \Lambda_H. Its low energy effective theory below \Lambda_H is described by the supersymmetric standard model with the ... More

New physics from Higgs self-coupling measurementOct 04 2004Radiative correction to the triple Higgs boson coupling is studied in the two Higgs doublet model in connection with the electroweak baryogenesis. It is shown that the one loop correction is large enough to be identified in future linear collider experiments, ... More

Probing Models of Dirac Neutrino Masses via the Flavor Structure of the Mass MatrixMar 29 2016May 25 2016We classify models of the Dirac neutrino mass by concentrating on flavor structures of the mass matrix. The advantage of our classification is that we do not need to specify detail of models except for Yukawa interactions because flavor structures can ... More

Search for Lepton Number Violating Charged Current Processes with Neutrino BeamsMay 25 2012We propose a new idea to test a class of loop-induced neutrino mass mechanisms by searching for lepton number violating charged current processes with incident of a neutrino beam. The expected rates of these processes are estimated based on some theoretical ... More

Screening Theorem for the Higgs Decays into the Gauge Boson PairsJan 17 1996The radiative corrections to the decays of the neutral CP-even Higgs boson $H$ into a longitudinal gauge boson pair, {\it i.e.}, $H \rightarrow Z_LZ_L$ and $W^+_LW^-_L$ are analyzed in the two Higgs doublet model by making use of the equivalence theorem. ... More

Potential for measuring the H^\pm W^\mp Z^0 vertex from WZ fusion at the Large Hadron ColliderDec 21 2006Mar 29 2007We investigate the possibility of measuring the H^\pm W^\mp Z^0 vertex from the single $H^\pm$ production process via WZ fusion at the CERN Large Hadron Collider (LHC). This vertex strongly depends on the structure of the Higgs sector in various new physics ... More

Multi-tau lepton signatures in leptophilic two Higgs doublet model at the ILCJan 31 2012We study the feasibility of the Type-X two Higgs doublet model (THDM-X) at collider experiments. In the THDM-X, new Higgs bosons mostly decay into tau leptons in the wide range of the parameter space. Such scalar bosons are less constrained by current ... More

Dimension-six top-Higgs interaction and its effect in collider phenomenologyJul 31 2006Measurement of the Yukawa interaction between the top quark and the Higgs boson should be useful to clarify the mechanism of fermion mass generation. We discuss the impact of non-standard interactions characterized by dimension-six operators on the effective ... More

Determination of tan(beta) from the Higgs boson decay at linear collidersMay 23 2013In the two Higgs doublet model, $\tan\beta$ is an important parameter, which is defined as the ratio of the vacuum expectation values of the doublets. We study how accurately $\tan\beta$ can be determined at linear colliders via the precision measurement ... More

Measurement of lepton flavor violating Yukawa couplings at ILCSep 01 2005We discuss lepton flavor violation (LFV) associated with tau leptons in the general 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 ... More

Radiative corrections to the Higgs boson couplings in the model with an additional real singlet scalar fieldNov 19 2015We 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 ... More

Probing exotic Higgs sectors from the precise measurement of Higgs boson couplingsJan 30 2013Jul 04 2013We study coupling constants of the standard model like Higgs boson with the gauge bosons $hZZ$ and $hWW$ and fermions $hf\bar{f}$ in the general Higgs sector which contains higher isospin representations with arbitrary hypercharge. In Higgs sectors with ... More

One-loop corrections to the Higgs self-couplings in the singlet extensionAug 04 2016We 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 ... More

Testing the dark matter scenario in the inert doublet model by future precision measurements of the Higgs boson couplingsMay 27 2016We evaluate radiative corrections to the Higgs boson couplings in the inert doublet model, in which the lightest component of the $Z_2^{}$ odd scalar doublet field can be a dark matter candidate. The one-loop contributions to the $hVV$, $hff$ and $hhh$ ... More

Testing the Higgs triplet model with the mass difference at the LHCOct 20 2011Mar 17 2012In general, there can be mass differences among scalar bosons of the Higgs triplet field with the hypercharge of Y=1. In the Higgs triplet model, when the vacuum expectation value $v_\Delta$ of the triplet field is much smaller than that $v$ ($\simeq ... More

Doubly-charged scalar bosons from the doubletMay 10 2011Nov 09 2011We consider the extended Higgs models, in which one of the isospin doublet scalar fields carries the hypercharge Y=3/2. Such a doublet field $\Phi_{3/2}$ is composed of a doubly charged scalar boson as well as a singly charged one. We first discuss a ... More

Neutrino mass, Dark Matter and Baryon Asymmetry via TeV-Scale Physics without Fine-TuningJul 02 2008Jan 07 2009We propose an extended version of the standard model, in which neutrino oscillation, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by the TeV-scale physics without assuming unnatural hierarchy among the mass scales. ... More

Triviality and vacuum stability bounds in the three-loop neutrino mass modelFeb 16 2011We study theoretical constraints on the parameter space under the conditions from vacuum stability and triviality in the three-loop radiative seesaw model with TeV-scale right-handed neutrinos which are odd under the $Z_2$ parity. In this model, some ... More

A TeV-scale model for neutrino mass, DM and baryon asymmetryJan 07 2009We discuss a model which would explain neutrino oscillation, dark matter, and baryon asymmetry of the Universe simultaneously by the physics at TeV scales. Tiny neutrino masses are generated at the three loop level due to the exact $Z_2$ symmetry, by ... More

SUSY Loop Contributions to the $W$-Pair Production in $e^+e^-$ CollisionsAug 12 2004We discuss one-loop contributions of supersymmetry (SUSY) particles to the process $e^+e^- \to W^+W^-$ in the minimal supersymmetric standard model. The calculation is tested by using the sum rule among the form factors, which is based on the BRS invariance. ... More

Complementarity in direct searches for additional Higgs bosons at the LHC and the International Linear ColliderApr 23 2014Jul 28 2014We discuss complementarity of discovery reaches of heavier neutral Higgs bosons and charged Higgs bosons at the LHC and the International Linear Collider (ILC) in two Higgs doublet models (2HDMs). We perform a comprehensive analysis on their production ... More

Electroweak baryogenesis and quantum corrections to the triple Higgs boson couplingNov 27 2004A phenomenological consequence of electroweak baryogenesis is studied in connection with the Higgs physics. In a two Higgs double model, the first order phase transition can be strong enough to allow the electroweak baryogenesis due to the effect of extra ... More

Mass bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet modelMar 08 1999Nov 11 1999The upper and the lower bounds of the lightest CP-even Higgs-boson mass ($m_h$) are discussed in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. They are obtained as a function of a cut-off scale $\Lambda$ ($\leq 10^{19}$ GeV) ... More

Novel Constraint on Parameter Space of the Georgi-Machacek Model by Current LHC DataJul 18 2014Nov 15 2014The same-sign diboson process $pp\to W^\pm W^\pm jj$ has been measured at the LHC using leptonic decay channels of the $W$ bosons, with production cross sections of two fiducial regions reported to be consistent with the standard model expectations within ... More

Lepton flavor violation in Higgs boson decays under the rare tau decay resultsMay 23 2005Jan 01 2006We 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 ... More

Diphoton excess at 750 GeV in an extended scalar sectorDec 30 2015Jan 07 2016We discuss an extended scalar model which explains the recent results of diphoton excess at 750 GeV at LHC Run II experiments. An additional singlet scalar boson with the mass of 750 GeV, which couples to top quarks via a dimension five operator, is produced ... More

Single and double production of the Higgs boson at hadron and lepton colliders in minimal composite Higgs modelsMar 17 2016In the composite Higgs models, originally proposed by Georgi and Kaplan, the Higgs boson is a pseudo Nambu-Goldstone boson (pNGB) of spontaneous breaking of a global symmetry. In the minimal version of such models, global SO(5) symmetry is spontaneously ... More

Testing neutrino mass generation mechanisms from the lepton flavor violating decay of the Higgs bosonJul 28 2016We investigate how observations of the lepton flavor violating decay of the Higgs boson ($h \to \ell\ell^\prime$) can narrow down models of neutrino mass generation mechanisms, which were systematically studied in Refs. [1,2] by focusing on the combination ... More

Renormalization of the Higgs sector in the triplet modelApr 09 2012Aug 05 2012We study radiative corrections to the mass spectrum and the triple Higgs boson coupling in the model with an additional Y=1 triplet field. In this model, the vacuum expectation value for the triplet field is strongly constrained from the electroweak precision ... More

Bounds on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenarioJul 24 2014A direct search for doubly-charged Higgs bosons $H^{\pm\pm}$ is one of the most important probe in the Higgs Triplet Model, which is motivated by generation mechanisms of tiny neutrino masses. There are two major decay modes of $H^{\pm\pm}$; i.e., the ... More

Testing Supersymmetry in $A H^\pm$ Associated ProductionFeb 21 2004In the Minimal Supersymmetric Standard Model, the masses of the charged Higgs boson ($H^\pm$) and the CP-odd scalar ($A$) are related by $M_{H^+}^2=M_A^2+m_W^2$ at the Born level. Because the coupling of $W^-$-$A$-$H^+$ is fixed by gauge interaction, ... More

Higgs coupling constants as a probe of new physicsAug 31 2004Aug 31 2004We study new physics effects on the couplings of weak gauge bosons with the lightest CP-even Higgs boson ($h$), $hZZ$, and the tri-linear coupling of the lightest Higgs boson, $hhh$, at the one loop order, as predicted by the two Higgs doublet model. ... More

Indirect reach of heavy MSSM Higgs bosons by precision measurements at future lepton collidersMay 14 2015Sep 11 2015In the Minimal Supersymmetric Standard Model (MSSM), the bottom Yukawa coupling of the Higgs boson can considerably deviate from its Standard Model prediction due to non-decoupling effects. We point out that the ratio of the Higgs boson decay branching ... More

Distinctive Higgs Signals of a Type II 2HDM at the LHCJan 02 2009Feb 26 2009We perform a numerical analysis of Higgs-to-Higgs decays within a Type II 2-Higgs Doublet Model (2HDM), highlighting several channels that cannot occur in its Supersymmetric version, thereby allowing one to possibly distinguish between these two scenarios. ... More

Can WIMP Dark Matter overcome the Nightmare Scenario?May 31 2010Even if new physics beyond the Standard Model (SM) 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 ... More

Electroweak phase transition and Higgs boson couplings in the model based on supersymmetric strong dynamicsNov 26 2012Apr 08 2013We discuss a strongly-coupled extended Higgs sector with the 126 GeV Higgs boson, which is a low-energy effective theory of the supersymmetric SU(2)$_H$ gauge thoery that causes confinement. In this effective theory, we study the parameter region where ... More