Flavour Mixing of Neutrinos and Baryon Asymmetry of the Universe

TL;DR

This paper explores how baryon asymmetry in the universe can be generated through neutrino flavor oscillations in the $ u$MSM, emphasizing the roles of neutrino mass hierarchy and CP violation.

Contribution

It provides analytical and numerical analysis of BAU generation via right-handed neutrino oscillations, highlighting the impact of neutrino mass hierarchy and mixing parameters.

Findings

Inverted hierarchy shows about 4% suppression compared to normal hierarchy.

Baryogenesis is ineffective when $ heta_{13}=0$ and $ heta_{23}=rac{ ext{pi}}{4}$ in the normal hierarchy.

Inverted hierarchy becomes significant for BAU when normal hierarchy conditions suppress baryogenesis.

Abstract

We investigate baryogenesis in the $\nu$MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when $\theta_{13}=0$ and $\theta_{23} = \pi/4$, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU.