Damping rates and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar theory - art. no. 065004

We study the transport coefficients, damping rates, and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma wi th the goal of understanding the main physical mechanisms that determine tr ansport of chirality in scenarios of nonlocal electroweak baryogenesis. The focus is on identifying the different transport coefficients for the diffe rent branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chir ality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust descript ion of the different damping rates and mean free paths for the soft collect ive excitations to leading order in HTL and lowest order in the Yukawa coup ling. The space-time evolution of wave packets of collective excitations un ambiguously reveals the respective mean free paths. We find that whereas bo th the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branche s is mainly determined by the decay of the heavy scalar into a hard fermion and a son collective excitation. We argue that these mechanisms are robust and are therefore relevant for nonlocal scenarios of baryogenesis either i n the standard model or extensions thereof.