The process R(L) ϩ R(L) Ϫ →W L ϩ W L Ϫ is studied with a view to discern the Higgs boson mass effects. The helicity amplitudes are evaluated retaining muon mass terms and cancellation of possible bad high energy behavior is discussed. The results are examined in the context of the equivalence theorem. The Higgs boson mass effects in the differential cross section (d/d cos ), total cross section ͑͒, and forward-backward asymmetry (A FB ) are presented for two cases: ͑i͒ m H Ͻ2m W and ͑ii͒ m H Ͼ2m W . Near the W L pair production threshold, both d/d cos and increase with an increase in ͱs for case ͑ii͒, while this trend is absent for case ͑i͒. Near resonance (ͱsϷm H ), d/d cos does not show an appreciable dependence on . For case ͑i͒ A FB is always positive, while for case ͑ii͒ A FB changes sign from negative to positive at ͱsϭm H . The A FB decreases with an increase in m H for any ͱsϾm H .

The helicity amplitudes for the process ϩ Ϫ →W ϩ W Ϫ are reevaluated with the inclusion of heavy neutrino mixing with the standard light neutrino. The effects of mixing are parametrized as a fractional change ⌬M * in the helicity amplitude for the t-channel exchange. The behavior of ⌬M * is examined. It is found that for a heavy neutrino mass m N ϭ10 GeV and scattering angle ϭ90°, ⌬M * ϭ0.007͉U N ͉ 2 at ͱs ϭ200 GeV and ⌬M * ϭ0.00002͉U N ͉ 2 at ͱsϭ800 GeV. The heavy neutrino mixing effects tend to vanish in the limit m N Ӷͱs even if the mixing element U N is large.

We explore the possibility of distinguishing the SM-like MSSM Higgs boson from the SM Higgs boson via Higgs boson pair production at future muon collider. We study the behavior of the production cross-section in SM and MSSM with Higgs boson mass for various MSSM parameters tan β and m A. We observe that at fixed CM energy, in the SM, the total cross-section increases with the increase in Higgs boson mass whereas this trend is reversed for the MSSM. The changes that occur for the MSSM in comparison to the SM predictions are quantified in terms of the relative percentage deviation in crosssection. The observed deviations in cross-section for different choices of Higgs boson masses suggest that the measurements of the cross-section could possibly distinguish the SM-like MSSM Higgs boson from the SM Higgs boson. Keywords.Higgs boson; standard model; minimal supersymmetric standard model; SMlike MSSM Higgs boson.

We examine the effects of mixing induced non-diagonal light-heavy neutrino weak neutral currents on the amplitude for the process v ava ZZ (with a e µ or τ). By imposing constraint that the amplitude should not exceed the perturbative unitarity limit at high energy´Ôs Λµ, we obtain bounds on light-heavy neutrino mixing parameter sin 2 θ v a L where θ v a L is the mixing angle. In the case of one heavy neutrino (mass m ξ ) or mass degenerate heavy neutrinos, for Λ 1 TeV, no bound is obtained for m ξ 0 50 TeV. However, sin 2 θ v a L 3 8 ¢ 10 6 for m ξ 5 TeV and sin 2 θ v a L 6 0¢10 8 for m ξ 10 TeV. For Λ ∞, no constraint is obtained for m ξ 0 99 TeV and sin 2 θ v a L 3 8 ¢10 2 (for m ξ 5 TeV) and sin 2 θ v a L 9 6 ¢10 3 (for m ξ 10 TeV).

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