Impact of Light Higgs Properties on the Determination of tan⁡β\tan\beta and msusym_{susy}

We examine whether parameters related to the Higgs sector of the minimal supersymmetric standard model can be determined by detailed study of the production cross section and decay branching ratios of the Higgs boson. Assuming that only the light Higgs boson will be observed at a future $e^+e^-$ linear collider with $\sqrt{s}=300\sim500$ GeV, we show that values of $m_{susy}$ and $\tan\beta$ are restricted within a narrow region in the $m_{susy}$ versus $\tan\beta$ plane by the combined analysis of the light Higgs properties. It is also pointed out that, in some case, $\tan\beta$ may be restricted to a relatively small value, $\tan\beta=1\sim5$.Comment: 7 pages with 10 figures, to be published in Prog. Theor. Phy

Production of Scalar Higgs and Pseudoscalar Higgs in Multi-Higgs Doublet Models at γγ\gamma\gamma Colliders

We present the effects of heavy CP-even (H) and CP-odd (A) Higgs bosons on the production cross section of the process $\gamma\gamma$ $\to t\bar{t}$ at the energy around the mass poles of the Higgs bosons. It is found that the interference between H and A with the small mass gap, as well as the ones between Higgs bosons and the continuum, contributes to the cross section, if the photon beams are polarized and if we observe the helicity of the top quarks. It is demonstrated in the framework of the minimal supersymmetric extension of the standard model that the H and A contributions can be sizable at future $\gamma\gamma$ colliders for small value of $\tan\beta$. The methods to measure the CP-parity of the Higgs boson are also presented. The statistical significances of detecting the Higgs signals and measuring the Higgs CP-parity are evaluated.Comment: 23 pages, LATEX file with 8 PS figures, to be published in Eur.Phys.J.

Neutral Scalar Higgs Masses and Production Cross Sections in an Extended Supersymmetric Standard Model

Upper bounds on the three neutral scalar Higgs masses are considered in the supersymmetric standard model with a gauge singlet Higgs field. When the lightest Higgs is singlet-dominated the second lightest Higgs is shown to lie near or below the theoretical upper bound on the lightest Higgs mass. We also consider detectability of these Higgs bosons at a future $e^+ e^-$ linear collider with $\sqrt{s}\sim 300$ GeV and show that at least one of the neutral scalar Higgs has a production cross section larger than 0.04~pb.Comment: Latex 9 pages + 5 figures (not included), KEK-TH-386, KEK preprint 93-204, CHIBA-EP-7

Probing the heavy Higgs mass by the measurement of the Higgs decay branching ratios in the minimal supersymmetric standard model

We examine whether the parameters in the Higgs sector of the minimal supersymmetric standard model can be determined by detailed study of production cross section and decay branching ratios of the Higgs particle. Assuming that the lightest CP-even Higgs boson ($h$) is observed at a future $e^+ e^-$ linear collider with $\sqrt{s}=300\sim500$GeV, we show that the value of CP-odd scalar mass is determined from the ratio of the two branching ratios, $Br(h\to b\bar{b})$ and $Br(h\to c\bar{c})+Br(h\to gg)$, almost independently of the stop mass scale.Comment: 12 pages, 3 figures, also available via anonymous ftp at ftp://ftp.kek.jp/kek/preprints/TH/TH-45

Probing Noncommutative Space-Time in the Laboratory Frame

The phenomenological investigation of noncommutative space-time in the laboratory frame are presented. We formulate the apparent time variation of noncommutativity parameter $\theta_{\mu\nu}$ in the laboratory frame due to the earth's rotation. Furthermore, in the noncommutative QED, we discuss how to probe the electric-like component $\overrightarrow{\theta_{E}}=(\theta_{01},\theta_{02},\theta_{03})$ by the process $e^-e^+\to\gamma\gamma$ at future $e^-e^+$ linear collider. We may determine the magnitude and the direction of $\overrightarrow{\theta_{E}}$ by detailed study of the apparent time variation of total cross section. In case of us observing no signal, the upper limit on the magnitude of $\overrightarrow{\theta_E^{}}$ can be determined independently of its direction.Comment: 12 pages, 7 figures, typos are corrected, one graph have been added in figure