In the electroweak phase transition there arises the problem of baryon number washout by sphaleron transitions, which can be avoided if the phase transition is strongly enough first order. The minimal supersymmetric standard model has just two Higgs doublets H 1 and H 2 , while the next to minimal model, NMSSM, has an additional singlet, N, this latter giving rise to the helpful feature that the Higgs potential contains a tree level trilinear field term. We use the tunneling criterion for the existence of a first order electroweak phase change. A quantitative statistical analysis indicates that with parameters of the NMSSM satisfying the experimental constraints a strong first order phase change occurs in about 50% of cases.

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