Phenomenology of Baryogenesis from Lepton-Doublet Mixing

TL;DR

This paper explores how mixing lepton doublets in the Standard Model can generate lepton asymmetries in the early universe, providing a detailed diagrammatic approach and analyzing implications for baryogenesis.

Contribution

It introduces a diagrammatic representation of lepton-flavour asymmetry generation from lepton-doublet mixing and examines the impact on reheat temperature bounds in leptogenesis models.

Findings

Lower bound on reheat temperature is about 1.2×10^9 GeV for two right-handed neutrinos.

Three right-handed neutrinos allow lower reheat temperatures with fine-tuned Yukawa couplings.

Correlation analysis between lepton flavours at different temperatures.

Abstract

Mixing lepton doublets of the Standard Model can lead to lepton flavour asymmetries in the Early Universe. We present a diagrammatic representation of this recently identified source of $CP$ violation and elaborate in detail on the correlations between the lepton flavours at different temperatures. For a model where two sterile right-handed neutrinos generate the light neutrino masses through the see-saw mechanism, the lower bound on reheat temperatures in accordance with the observed baryon asymmetry turns out to be $\gsim 1.2\times 10^9\,{\rm GeV}$. With three right-handed neutrinos, substantially smaller values are viable. This requires however a tuning of the Yukawa couplings, such that there are cancellations between the individual contributions to the masses of the light neutrinos.