Status of rates and rate equations for thermal leptogenesis

TL;DR

This paper reviews recent advances in calculating the thermal rates and equations governing heavy neutrino dynamics in leptogenesis, emphasizing the strong washout regime and the importance of thermal effects.

Contribution

It provides a comprehensive review of the thermal field theoretic derivation of key quantities and evolution equations relevant for leptogenesis in the strong washout regime.

Findings

Updated calculations of heavy neutrino production rates

Refined CP asymmetry estimates in thermal environments

Improved understanding of washout processes in leptogenesis

Abstract

In many realizations of leptogenesis, heavy right-handed neutrinos play the main role in the generation of an imbalance between matter and antimatter in the early Universe. Hence, it is relevant to address quantitatively their dynamics in a hot and dense environment by taking into account the various thermal aspects of the problem at hand. The strong washout regime offers an interesting framework to carry out calculations systematically and reduce theoretical uncertainties. Indeed, any matter-antimatter asymmetry generated when the temperature of the hot plasma $T$ exceeds the right-handed neutrino mass scale $M$ is efficiently erased, and one can focus on the temperature window $T \ll M$. We review recent progresses in the thermal field theoretic derivation of the key ingredients for the leptogenesis mechanism: the right-handed neutrino production rate, the CP asymmetry in the heavy-neutrino decays and the washout rates. The derivation of evolution equations for the heavy-neutrino and lepton-asymmetry number densities, their rigorous formulation and applicability are also discussed.