AVOIDING BARYON WASHOUT IN THE EXTENDED STANDARD MODEL

It has been shown recently, in a one-loop analysis, that adding a singlet to the standard model strengthens the first-order nature of the electroweak phase transition, and thus weakens the upper limit on the Higgs boson mass required for successful baryogenesis. We demonstrate that the inclusion of ring diagrams alters the argument for a light singlet, consequently weakening the Higgs boson mass bound only up to approximately m(W). However, the addition of several light singlets, or a heavy singlet, can raise the bound still further.