Fluctuation-driven electroweak phase transition

We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs boson masses in the range 57≤${\mathit{m}}_{\mathit{H}}$≤150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, due to efficient thermal nucleation of subcritical fluctuations of the asymmetric phase within the symmetric phase. We propose that the transition to the asymmetric vacuum is completed by percolation of these fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order electroweak transition.