Flavoured Leptogenesis in the CTP Formalism

TL;DR

This paper develops a framework using the CTP formalism to derive kinetic equations for leptogenesis that incorporate multiple lepton flavours, revealing how flavour-sensitive processes and gauge interactions influence lepton asymmetry evolution.

Contribution

It introduces a novel derivation of kinetic equations for flavoured leptogenesis within the CTP formalism, accounting for flavour oscillations and decoherence effects.

Findings

Lepton flavour oscillations are overdamped due to rapid gauge interactions.

The kinetic equations interpolate between unflavoured and fully flavoured regimes.

Numerical solutions show the transition in the intermediate parametric region.

Abstract

Within the Closed Time Path (CTP) framework, we derive kinetic equations for particle distribution functions that describe leptogenesis in the presence of several lepton flavours. These flavours have different Standard-Model Yukawa couplings, which induce flavour-sensitive scattering processes and thermal dispersion relations. Kinetic equilibrium, which is rapidly established and maintained via gauge interactions, allows to simplify these equations to kinetic equations for the matrix of lepton charge densities. In performing this simplification, we notice that the rapid flavour-blind gauge interactions damp the flavour oscillations of the leptons. Leptogenesis turns out to be in the parametric regime where the flavour oscillations are overdamped and flavour decoherence is mainly induced by flavour sensitive scatterings. We solve the kinetic equations for the lepton number densities numerically and show that they interpolate between the unflavoured and the fully flavoured regimes within the intermediate parametric region, where neither of these limits is applicable.