Standard model CP-violation and baryon asymmetry (II). Finite temperature

Abstract We consider quantum effects in a world with two coexisting symmetry phases, unbroken and spontaneously broken, as a result of a first order phase transition. The discrete symmetries of the problem are discussed in general. We compute the exact two-point Green function for a free fermion, when a thin wall separates the two phases. The Dirac propagator displays both massive and massless poles, and new CP -even phases resulting from the fermion reflection on the wall. We discuss the possible quark-antiquark CP -asymmetries produced in the Standard Model (SM) for the academic T = 0 case. General arguments indicate that an effect first appears at order α W in the reflection amplitude, as the wall acts as a source of momentum and the on-shell one-loop self-energy cannot be renormalized away. The asymmetries stem from the interference of the SM CP -odd couplings and the CP -even phases in the propagator. We perform a toy computation that indicates the type of GIM cancellations of the problem. The behaviour can be expressed in terms of two unitarity triangles.