SUSY and the electroweak phase transition

We analyze the effective three-dimensional theory previously constructed for the MSSM and multi-Higgs models to determine the regions of parameter space in which the electroweak phase transition is sufficiently strong for a B + L asymmetry to survive in the low-temperature phase. We find that the inclusion of all supersymmetric scalars and all one-loop corrections has the effect of enhancing the strength of the phase transition. Without a light stop or extension of the MSSM the phase transition is sufficiently first order only if the lightest Higgs mass Mh ≲ 70 GeV and tan β ≲ 1.75.