Hard-Thermal-Loop Corrections in Leptogenesis II: Solving the Boltzmann Equations

TL;DR

This paper studies how hard-thermal-loop corrections affect lepton asymmetry in leptogenesis by solving Boltzmann equations with various thermal and zero-temperature approximations, revealing significant differences in outcomes.

Contribution

It provides a detailed analysis of HTL corrections in leptogenesis, including the effects of leptonic quasiparticles and different interaction regimes, which was not thoroughly explored before.

Findings

Thermal corrections significantly alter lepton asymmetry compared to vacuum case.

Lepton modes in thermal plasma can enhance asymmetry by up to a factor of two.

Different thermal and zero-temperature approximations lead to notable variations in results.

Abstract

We investigate hard-thermal-loop (HTL) corrections to the final lepton asymmetry in leptogenesis. To this end we solve the Boltzmann equations with HTL-corrected rates and CP asymmetries, which we calculated in paper I of this series. We pay special attention to the influence of the two leptonic quasiparticles that arise at non-zero temperature. We include only decays and inverse decays and allow for the lepton modes to be either decoupled from each other, or to be in chemical equilibrium by some strong interaction, simulating the interaction with gauge bosons. In two additional cases, we approximate the full HTL lepton propagators with zero-temperature propagators, where we replace the zero-temperature mass by the thermal mass of the leptons $m_\ell(T)$ or the asymptotic mass $\sqrt{2} \, m_\ell(T)$. We compare the final lepton asymmetries of the four thermal cases and the zero-temperature case for zero, thermal and dominant initial neutrino abundance. The final lepton asymmetries of the thermal cases differ considerably from the vacuum case and from each other in the weak washout regime for zero initial neutrino abundance and in the intermediate regime for dominant initial neutrino abundance. In the strong washout regime, the final lepton asymmetry can be enhanced by a factor of two in the case of strongly interacting lepton modes.