Two Stage Phase Transition in Two Higgs Models

We present a mechanism in which models with two Higgs fields can undergo a two stage phase transition as the temperature falls. The first stage is a conventional second order (or weakly first order) transition in which the symmetry is broken. Shortly thereafter follows a first order transition with barrier penetration, bubble production and loss of thermal equilibrium. For Higgs potentials with CP violation, we show that the second stage of the transition has all the features required for weak scale baryogenesis.