Higgs Physics as a Proble of New Physics

The 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 is a possibility of non-minimal Higgs sectors. While the standard model is not contradict with the current data at the LHC within the error, most of extended Higgs sectors can also reproduce the data. An extended Higgs sector often appears in a new physics model beyond the standard model, so that we can determine new physics from the Higgs sector. In this talk, we discuss various aspects of extended Higgs sectors, in particular its phenomenological properties and testability at future experiments at the International Linear Collider.Comment: 6 pages, 3 figures, prepared for Proceedings of LC13 Workshop: exploring QCD from the infrared regime to heavy flavour scales at B-factories, the LHC and a Linear Collider, 16-20 September 2013, ECT*, Villa Tambosi, Villazzano (TN), Ital

Search for lepton flavor violation via the intense high-energy muon beam

A deep inerastic scattering process \mutau is discussed to study lepton flavor violation between muons and tau leptons. In supersymmetric models, the Higgs boson mediated diagrams could be important for this reaction. We find that at a muon energy ($E_{\mu}$) higher than 50 GeV, the predicted cross section significantly increases due to the contribution from sea $b$-quarks. The number of produced tau leptons can be $\mathcal{O}(10^4)$ at $E_{\mu}$= 300 GeV from $10^{20}$ muons, whereas $\mathcal{O}(10^2)$ events are given at $E_{\mu}= 50$ GeV.Comment: Contribution to the 6th International Workshop on Neutrino Factories & Superbeams(NuFact04), Jul. 26-Aug. 1, 2004, Osaka Univerisity, Osaka, Japan, talk given by S.K., to appear in the Proceedings, 3 pages, 4 figure

The H±W∓Z0H^\pm W^\mp Z^0 vertex and single charged Higgs boson production via WZWZ fusion at the Large Hadron Collider

There 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 structure of the model, so that its experimental determination can be useful to test each scenario. We discuss predictions on this coupling in several models, such as the model with additional real and complex triplets, the Littlest Higgs model, the two Higgs doublet model and the minimal supersymmetric standard model. In order to measure the $H^\pm W^\mp Z^0$ coupling we consider single $H^\pm$ production via the $WZ$ fusion mechanism at the CERN Large Hadron Collider. The production rate is hierarchically different among these models, so that this process can be useful to explore new physics scenarios.Comment: 14 pages, 2 figures, revtex4, references added, typo correcte

Probing Models of Neutrino Masses via the Flavor Structure of the Mass Matrix

We 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 while determination of the overall scale of the mass matrix requires to specify also the scalar potential and masses of new particles. Thus, models to generate Majorana neutrino mass matrix can be efficiently classified according to the combination of Yukawa interactions. We first investigate the case where Yukawa interactions with only leptons are utilized. Next, we consider the case with Yukawa interactions between leptons and gauge singlet fermions, which have the odd parity under the unbroken Z_2 symmetry. We show that combinations of Yukawa interactions for these cases can be classified into only three groups. Our classification would be useful for the efficient discrimination of models via experimental tests for not each model but just three groups of models.Comment: 14 pages, 9 eps files, references adde

Unitarity bound in the most general two Higgs doublet model

We 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 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 the conserved quantum numbers at high energies. Imposing the condition of perturbative unitarity to the eigenvalues of the scattering matrix, constraints on the model parameters can be obtained. We apply our results to constrain the mass range of the next--to--lightest Higgs state in the model.Comment: Version published in Physics Letters

Heavy charged Higgs boson production at next generation γγ\gamma\gamma colliders

We investigate the scope of all relevant production modes of charged Higgs bosons in the MSSM, with mass larger than the one of the top quark, at future Linear Colliders operating in $\gamma\gamma$ mode at the TeV energy scale. Final states with one or two $H^\pm$ bosons are considered, as produced by both tree- and loop-level interactionsComment: 11 pages, latex, 6 figure

Higgs boson pair production at a photon-photon collision in the two Higgs doublet model

We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson ($h$) has the standard model like couplings to the gauge bosons. We take into account the one-loop correction to the $hhh$ coupling as well as additional one-loop diagrams due to charged Higgs bosons to the $\gamma\gamma\to hh$ helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the $hhh$ coupling measurement at the photon collider.Comment: 16 pages, 8 figures; added Appendix with a figur