NONLOCAL ELECTROWEAK BARYOGENESIS .2. THE CLASSICAL REGIME

We investigate baryogenesis at a first-order electroweak phase transit ion in the presence of a CP-violating condensate on the bubble walls, in the regime in which the bubble walls are ''thick,'' in the sense th at fermions interact with the plasma many times as the bubble wall pas ses. Such a condensate is present in multi-Higgs-doublet extensions of the standard model and may be formed via an instability in the minima l standard model. We concentrate on particles with typical thermal ene rgies in the plasma, whose interactions with the wall are accurately d escribed by the WKB approximation, in which a classical chiral force i s evident. The deviations from thermal equilibrium produced by the mot ion of the wall are then treated using a classical Boltzmann equation which we solve in a fluid approximation. From the resulting equations we find two effects important for baryogenesis: (i) a classical chiral force term due to the CP-violating background and (ii) a term arising from hypercharge-violating interactions which are pushed out of equil ibrium by the background field. Provided the wall propagates slower th an the speed of sound, both terms lead to the diffusion of a chiral as ymmetry in front of the wall. This can produce a baryon asymmetry of t he observed magnitude for typical wall velocities and thicknesses.