Robustness of ARS Leptogenesis in Scalar Extensions

TL;DR

This paper examines how adding a scalar singlet to the Standard Model with sterile neutrinos impacts ARS leptogenesis, showing that scalar interactions generally reduce the generated baryon asymmetry.

Contribution

It demonstrates that the presence of a thermalized scalar singlet typically diminishes the baryon asymmetry produced by ARS leptogenesis in models with sterile neutrinos.

Findings

Scalar decays produce additional sterile neutrinos, reducing asymmetry.

The effect depends on scalar and neutrino properties.

Results inform future laboratory searches for sterile neutrinos and scalars.

Abstract

Extensions of the Standard Model (SM) with sterile neutrinos are well motivated from the observed oscillations of the light neutrinos and they have shown to successfully explain the Baryon Asymmetry of the Universe (BAU) through, for instance, the so-called ARS leptogenesis. Sterile neutrinos can be added in minimal ways to the SM, but many theories exist where sterile neutrinos are not the only new fields. Such theories often include scalar bosons, which brings about the possibility of further interactions between the sterile neutrinos and the SM. In this paper we consider an extension of the SM with two sterile neutrinos and one scalar singlet particle and investigate the effect that an additional, thermalised, scalar has on the ARS leptogenesis mechanism. We show that in general the created asymmetry is reduced due to additional sterile neutrino production from scalar decays. When sterile neutrinos and scalars are discovered in the laboratory, our results will provide information on the applicability of the ARS leptogenesis mechanism.