Hiroshi Yokoya

Fingerprinting nonminimal Higgs sectors

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

First constraint on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario at the LHC

Z_2

Tau polarization in tau neutrino nucleon scattering

symmetry. Second, precision measurements of the Higgs boson couplings at future experiments can be used for the indirect search of extended Higgs sectors if 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 which 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 non-minimal Higgs sector even without direct discovery of additional Higgs bosons at the LHC.

Bounds on the mass of doubly-charged Higgs bosons in the same-sign diboson decay scenario

Abstract When the doubly-charged Higgs bosons H ± ± 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 for the case where the same-sign diboson decay H ± ± → W ± ( ⁎ ) W ± ( ⁎ ) is dominant. We study limits on the mass for such a case by using the current experimental data. From the precise measurement of the total width of the Z boson at the LEP experiment, the mass below 43 GeV is excluded with the 95% confidence level. It turns out that the results from four charged-lepton searches at LEP do not provide any significant constraint. We show that a new lower bound is obtained in the diboson decay scenario at the LHC with the collision energy to be 7 TeV and the integrated luminosity to be 4.7 fb − 1 . By using the data of the same-sign dilepton events, the lower limit is found to be 60 GeV at the 95% confidence level. By the extrapolation of the data to 20 fb − 1 with the same collision energy, the lower limit is evaluated to be 85 GeV.

Weight function method for precise determination of top quark mass at Large Hadron Collider

Abstract We investigate the spin polarization of τ ± leptons produced in ν τ and ν τ nucleon scattering via charged currents. Quasi-elastic scattering, Δ resonance production and deep inelastic scattering processes are studied. The polarization information is essential for measuring the τ ± appearance rate in long baseline neutrino oscillation experiments, because the decay particle distributions depend crucially on the τ ± spin. In this article, we calculate the spin density matrix of each process and estimate the spin polarization vector in medium and high neutrino energy interactions. We find that the produced τ ± s have high degree of polarization, and their spin direction depends non-trivially on the energy and the scattering angle of τ ± in the laboratory frame.

Reconstruction of inert doublet scalars at the international linear collider

A direct search for doubly-charged Higgs bosons

Discrimination of models including doubly charged scalar bosons by using tau lepton decay distributions

H^{\pm\pm}

Complementarity in direct searches for additional Higgs bosons at the LHC and the International Linear Collider

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

Measuring the top Yukawa coupling at the ILC at

H^{\pm\pm}

\sqrt{s}=500

; i.e., the same-sign dilepton decay