CP asymmetry in heavy Majorana neutrino decays at finite temperature: the nearly degenerate case

TL;DR

This paper calculates thermal corrections to CP asymmetries in nearly degenerate heavy Majorana neutrino decays, crucial for understanding leptogenesis and baryon asymmetry in the universe.

Contribution

It provides a systematic effective field theory approach to compute thermal corrections for nearly degenerate Majorana neutrinos, extending previous analyses.

Findings

Thermal corrections to CP asymmetries are quantified at finite temperature.

Leading order thermal effects are derived in an effective field theory framework.

Results are applicable for temperatures below neutrino masses but above the electroweak scale.

Abstract

In a model where Majorana neutrinos heavier than the electroweak scale couple to Standard Model Higgs bosons and leptons, we compute systematically thermal corrections to the direct and indirect CP asymmetries in the Majorana neutrino decays. These are key ingredients entering the equations that describe the thermodynamic evolution of the induced lepton-number asymmetry eventually leading to the baryon asymmetry in the universe. We compute the thermal corrections in an effective field theory framework that assumes the temperature smaller than the masses of the Majorana neutrinos and larger than the electroweak scale, and we provide the leading corrections in an expansion of the temperature over the mass. In this work, we consider the case of two Majorana neutrinos with nearly degenerate masses.