Electroweak Phase Transition in the Early Universe ?

Existence and properties of the electroweak phase transition in the early universe depend strongly on the mass of the Higgs scalar M_H. There is presumably no true symmetry restoration at high temperature. Nevertheless, a first order phase transition occurs in the standard model for M_H smaller than about 70 GeV. For a realistic scalar mass M_H larger than about 70 GeV the transition to the high temperature regime is described by a crossover, due to the strong electroweak gauge interactions for temperatures near and above the critical temperature. Electroweak baryogenesis during this transition seems not possible within the standard model. The observed baryon asymmetry in the universe therefore implies the necessity of an extension of the standard model.