Low-Scale Leptogenesis from Resonant Thermal Lepton Flavour Coherences

TL;DR

This paper introduces a new mechanism for low-scale leptogenesis that leverages resonant thermal lepton-flavour coherences, enabling successful baryogenesis with neutrino masses as low as GeV.

Contribution

The study develops a flavour-covariant formalism revealing a novel dominant leptogenesis mechanism enhanced by thermal coherences, independent of neutrino mass degeneracy.

Findings

Mechanism works for both Dirac and Majorana neutrinos.

Leptogenesis can be successful with neutrino masses as low as GeV.

Resonant thermal lepton-flavour coherences significantly enhance asymmetry generation.

Abstract

Resonant heavy-neutrino mixing and sterile neutrino oscillations are two prominent mechanisms to realize low-scale leptogenesis, with singlet neutrino masses below TeV energies that could be probed in current and future laboratory experiments. In their minimal settings, both mechanisms require a significant degree of degeneracy in the singlet neutrino masses to compensate for the suppression that results from the small neutrino Yukawa couplings. After further developing the flavour-covariant Kadanoff-Baym formalism, we study in detail a novel dominant mechanism for low-scale leptogenesis which becomes greatly enhanced by resonant thermal lepton-flavour coherences at the two-loop level. This mechanism works successfully for both Dirac and Majorana singlet neutrinos, and it does not rely on whether these singlet neutrinos are quasi-degenerate or not. In particular, it implies that successful low-scale leptogenesis in the type-I seesaw framework can be naturally realised with heavy neutrino masses that could be as low as GeV.