The Effective Potential of Electroweak Theory with Two Massless Higgs Doublets at Finite Temperature

The effective potential of electroweak theory with two massless Higgs doublets at finite temperature is studied. We investigate phase structure and critical temperature in this model by numerical analysis without high-temperature expansion. The phase transition is found to be of first order. The critical temperature is shown to be relatively low for typical scalar masses. The free energy of the critical bubble is calculated with some approximations and we find that the bubble nucleation can occur at a temperature a little below the critical temperature. We also discuss the possibility of the electroweak baryogenesis.