Freeze-in leptogenesis with sterile neutrino self-interactions

TL;DR

This paper explores how sterile neutrino self-interactions mediated by a scalar singlet can enhance freeze-in leptogenesis, reducing the need for precise mass degeneracy and potentially explaining the baryon asymmetry of the universe.

Contribution

It introduces a scalar singlet extension to the Standard Model that boosts baryon asymmetry generation via sterile neutrino self-interactions, alleviating fine-tuning in ARS leptogenesis.

Findings

Effective potential can increase baryon asymmetry by several orders of magnitude.

Scalar interactions relax the mass degeneracy requirement in ARS leptogenesis.

New Yukawa interactions influence sterile neutrino production and destruction rates.

Abstract

Sterile neutrinos are a simple yet compelling addition to the Standard Model. For right-handed neutrinos with masses below the electroweak scale, leptogenesis can proceed through CP-violating oscillations of the sterile neutrinos. This is known as ARS or freeze-in leptogenesis. However, the ARS scenario requires the right-handed neutrinos to have a high degree of mass degeneracy. In this work, we study an extension of the SM that introduces a scalar singlet in addition to the two sterile neutrinos required to generate the baryon asymmetry. The new scalar interacts with the sterile neutrinos via a Yukawa interaction. This leads to an additional rate for the production and destruction of the sterile neutrinos and to a novel contribution to the effective potential. For the case in which the mass and the new Yukawa matrices are not diagonal in the same basis, we find that the effective potential can boost the baryon asymmetry of the universe by several orders of magnitude. This significantly alleviates the fine-tuned mass condition required in vanilla ARS leptogenesis.