Baryogenesis from Mixing of Lepton Doublets

TL;DR

This paper demonstrates that mixing of lepton doublets in the Standard Model can significantly contribute to lepton asymmetry generation during the early Universe, especially for certain neutrino mass ratios, impacting baryogenesis models.

Contribution

It introduces a novel mechanism where lepton doublet mixing contributes substantially to lepton asymmetry, accounting for gauge and Yukawa interactions, and compares it to existing decay-based contributions.

Findings

Lepton mixing contribution is large for neutrino mass ratios of a few.

Asymmetry is suppressed for large hierarchies in neutrino masses.

Lepton mixing can dominate in intermediate mass hierarchy scenarios.

Abstract

It is shown that the mixing of lepton doublets of the Standard Model can yield sizeable contributions to the lepton asymmetry, that is generated through the decays of right-handed neutrinos at finite temperature in the early Universe. When calculating the flavour-mixing correlations, we account for the effects of Yukawa as well as of gauge interactions. We compare the freeze-out asymmetry from lepton-doublet mixing to the standard contributions from the mixing and direct decays of right-handed neutrinos. The asymmetry from lepton mixing is considerably large when the mass ratio between the right-handed neutrinos is of order of a few, while it becomes Maxwell-suppressed for larger hierarchies. For an intermediate range between the case of degenerate right-handed neutrinos (resonant Leptogenesis) and the hierarchical case, lepton mixing can yield the main contribution to the lepton asymmetry.