GeV-scale hot sterile neutrino oscillations: a derivation of evolution equations

TL;DR

This paper derives evolution equations for GeV-scale sterile neutrinos and active lepton densities, incorporating detailed scattering processes and helicity effects, to better understand leptogenesis at high temperatures.

Contribution

It provides a systematic derivation of non-equilibrium evolution equations including helicity and scattering effects for sterile neutrinos at GeV scale.

Findings

Derived equations governing sterile neutrino and lepton densities.

Accounted for LPM resummation and all relevant scatterings.

Analyzed the decoupling of sphaleron processes.

Abstract

Starting from operator equations of motion and making arguments based on a separation of time scales, a set of equations is derived which govern the non-equilibrium time evolution of a GeV-scale sterile neutrino density matrix and active lepton number densities at temperatures T > 130 GeV. The density matrix possesses generation and helicity indices; we demonstrate how helicity permits for a classification of various sources for leptogenesis. The coefficients parametrizing the equations are determined to leading order in Standard Model couplings, accounting for the LPM resummation of 1+n <-> 2+n scatterings and for all 2 <-> 2 scatterings. The regime in which sphaleron processes gradually decouple so that baryon plus lepton number becomes a separate non-equilibrium variable is also considered.