Electroweak Baryogenesis in the Adiabatic Limit

Electroweak baryogenesis can occur in the ``adiabatic limit,'' in which expanding bubbles of true vacuum are assumed to have rather thick walls and be slowly moving. Here the problem of calculating the baryon asymmetry in this limit is reconsidered. A simple prescription for obtaining the relevant kinetic equations is given. An additional suppression beyond that usually assumed is found. This arises because the generation of an asymmetry requires violation of approximately conserved currents by Higgs expectation values, which are small near the front of the walls. As applications, the asymmetries in multi-Higgs models and the minimal supersymmetric standard model are estimated to be proportional to $\alpha_w^8$ and $\alpha_w^6$ respectively. Also, in this limit the baryon asymmetry in the Minimal Standard Model is extraordinarily small.