Decay of a Yukawa fermion at finite temperature and applications to leptogenesis

TL;DR

This paper calculates the decay rate of a Yukawa fermion at finite temperature using advanced thermal field theory techniques and applies it to leptogenesis, revealing significant deviations from traditional methods.

Contribution

It introduces a novel finite temperature calculation of fermion decay rates using cutting rules and Green's functions, improving leptogenesis modeling accuracy.

Findings

Decay rate differs by over an order of magnitude from traditional approaches.

Deviations are due to distinct leptonic dispersion relations at finite temperature.

Results impact the understanding of the weak washout regime in leptogenesis.

Abstract

We calculate the decay rate of a Yukawa fermion in a thermal bath using finite temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. We apply this result to the decay of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rate differs from the usual approach by more than one order of magnitude in the temperature range which is interesting for the weak washout regime. We discuss how to arrive at consistent finite temperature treatments of leptogenesis.