PUB - Publikationen an der Universität Bielefeld

We study the MSSM finite temperature electroweak phase transition with lattice Monte Carlo simulations, for a large Higgs mass (m(H) approximate to 95 GeV) and light stop masses (m(<(tau)over bar R>) similar to 150-160 GeV). We employ a 3d effective held theory approach, where the degrees of freedom appearing in the action are the SU(2) and SU(3) gauge fields, the weakly interacting Higgs doublet, and the strongly interacting stop triplet. We determine the phase diagram, the critical temperatures, the scaler field expectation values, the latent heat, the interface tension and the correlation lengths at the phase transition points. Extrapolating the results to the infinite volume and continuum limits, we find that the transition is stronger than indicated by 2-loop perturbation theory, guaranteeing that the MSSM phase transition is strong enough for baryogenesis in this regime. We also study the possibility of a two-stage phase transition, in which the stop field gets an expectation value in an intermediate phase, We find that a two-stage transition exists non-perturbatively, as well, but for somewhat smaller stop masses than in perturbation theory. Finally the latter stage of the two-stage transition is found to be extremely strong, and thus it might not be allowed in the cosmological environment. (C) 1998 Elsevier Science B.V.