Transport equations for chiral fermions to order ? and electroweak baryogenesis: Part II

This is the second in a series of two papers. While in Paper I [Ann. Phys. 314 (2004) 208] we derive semiclassical Boltzmann transport equations and study their flow terms, here we make use of the results from that paper and address the collision terms. We use a model Lagrangean, in which fermions couple to scalars through Yukawa interactions and approximate the self-energies by the one-loop expressions. This approximation already contains important aspects of thermalization and scatterings required for quantitative studies of transport in plasmas. We compute the CP-violating contributions to both the scalar and the fermionic collision term. CP-violating sources appear at order ? in gradient and in a weak coupling expansion, as a consequence of a CP-violating split in the fermionic dispersion relation. This represents the first controlled calculation of CP-violating collisional sources, thus establishing the existence of `spontaneous' baryogenesis sources in the collision term. The calculation is performed by the use of the spin quasiparticle states established in Paper I. Next, we present the relevant leading order calculation of the relaxation rates for the spin states and relate them to the more standard relaxation rates for the helicity states. We also analyze the associated fluid equations, make a comparison between the source arising from the semiclassical force in the flow term and the collisional source, and observe that the semiclassical source tends to be more important in the limit of inefficient diffusion/transport.