Measuring the Higgs CP property at a Photon Linear Collider

We study measurement of the CP property of the Higgs boson at a photon linear collider. One method where we take advantage of interference between Higgs-production and background amplitudes is proposed. A broad peak of the photon energy spectrum is helpful in observing the energy dependence of the interference effects. Numerical results for the process $\gamma \gamma \to t \bar{t}$ are shown as an example.Comment: 4 pages, 1 PS figure. Talk given at the Linear Collider Workshop 2000, Fermilab, Oct. 24 - 28, 200

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

Production of CP-even and CP-odd Higgs bosons at Muon colliders

In the $s$-channel Higgs-boson-exchange processes, the interference between the amplitudes for CP-even and CP-odd Higgs bosons is sizable, if the helicities of initial and final particles are properly fixed and if the mass difference between these bosons is not much larger than their decay widths. We discuss this interference effect in the process $\mu^+ \mu^-$ $\to t\bar{t}$. Examining the effects gives us information on CP-parity for Higgs bosons and on the sign of a product of the coupling constants for $H\mu^-\mu^+$, $Ht\bar{t}$, $A\mu^-\mu^+$ and $At\bar{t}$ vertices. The feasibility of observing the interference effect in future muon colliders is evaluated in the framework of the minimal supersymmetric extension of the standard model as an example.Comment: 18 pages, LATEX file with 3 PS figures, some comments and references adde

Contributions of vector-like quarks to radiative B meson decay

We study the decay B\to X_s\gamma in a minimal extension of the standard model with extra up- and down-type quarks whose left- and right-handed components are both SU(2) singlets. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix are obtained from the experimental results for the branching ratio. Even if the extra quarks are too heavy to be detected in near-future colliders, the branching ratio could have a value which is non-trivially different from the prediction of the standard model.Comment: 11 pages, LATEX file with 3 EPS figure

Enhancement of W+/- H-/+ Production at Hadron Colliders in the Two Higgs Doublet Model

We 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 study the possible enhancement of the THDM prediction for the cross section compared to the prediction of the Minimal Supersymmetric Standard Model (MSSM). We find regions in the THDM parameter space where the THDM prediction can exceed the one of the MSSM by two orders of magnitude. These regions of large cross section are in agreement with theoretical bounds on the model, derived from the requirement of vacuum stability and perturbative unitarity, and are not excluded by experimental constraints.Comment: 19 pages, 5 figure