ON THE ELECTROWEAK PHASE-TRANSITION IN THE MINIMAL SUPERSYMMETRIC STANDARD MODEL

We study the finite-temperature effective potential of the Minimal Sup ersymmetric Standard Model, in the limit of only one light Higgs boson . Because of the large top Yukawa coupling, there can be significant d ifferences with respect to the Standard Model case: for given values o f the Higgs and top masses, little supersymmetry breaking in the stop sector can make the phase transition more strongly first-order. After including the full structure of the stop mass matrix, the most importa nt experimental constraints and the leading plasma effects, we find th at the present limits on Higgs and squark masses are still compatible with the scenario of electroweak baryogenesis, in a small region of pa rameter space corresponding to m(h) less than or similar too 70 GeV an d m(b1)approximately less than or similar to 105 GeV.