Lepton number violation as a key to low-scale leptogenesis

TL;DR

This paper investigates low-scale leptogenesis via sterile neutrino oscillations, proposing a framework with minimal sterile states and lepton number violation to generate the observed baryon asymmetry at electroweak scale.

Contribution

It introduces a novel minimal model with two sterile states for successful leptogenesis, extending the Inverse Seesaw with a Linear Seesaw term, and provides analytical and numerical analysis of the mechanism.

Findings

Leptogenesis can occur at electroweak scale through sterile neutrino oscillations.

A natural origin of mass degeneracy in sterile states is identified.

Analytical expression for baryon asymmetry in weak washout regime is revisited.

Abstract

We explore the possibility of having a successful leptogenesis through oscillations between new sterile fermion states added to the Standard Model field content in a well motivated framework, naturally giving rise to the required mass splitting between the sterile states through a small total lepton number violation. We propose a framework with only two sterile states forming a pseudo-Dirac state, in which their mass difference as well as the smallness of the neutrino masses are due to two sources of lepton number violation with $\Delta L=2$, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term. We also explore the pure Inverse Seesaw mechanism in its minimal version, requiring at least four new sterile states in order to comply with neutrino data. Our analytical and numerical studies reveal that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between the two sterile states with a "natural" origin of the strong degeneracy in their mass spectrum. We also revisit the analytical expression of the baryon asymmetry of the Universe in the weak washout regime of this framework.