Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models

TL;DR

This paper investigates how neutrino oscillations in four-neutrino models influence neutrino asymmetries and Big Bang Nucleosynthesis, improving previous models by including finite repopulation and momentum distribution effects.

Contribution

It provides a detailed analysis of neutrino asymmetry evolution in four-neutrino models, incorporating finite repopulation rates and momentum distribution distortions for the first time.

Findings

Neutrino oscillations can generate significant neutrino asymmetries affecting BBN.

The improved model refines predictions of neutrino distributions during early universe.

Results constrain neutrino mass differences relevant for cosmology.

Abstract

We re-examine the evolution of neutrino asymmetries in several four neutrino models. The first case involves the direct creation of $L_{\nu_e}$ by $\nu_e \leftrightarrow \nu_s$ oscillations. In the second case, we consider the mass hierarchy $m_{\nu_\tau} \gg m_{\nu_\mu}, m_{\nu_e}, m_{\nu_s}$ where $\nu_\tau \leftrightarrow \nu_s$ oscillations generate a large $L_{\nu_\tau}$ and some of this asymmetry is converted into $L_{\nu_e}$ by $\nu_{\tau} \leftrightarrow \nu_{e}$ oscillations. We estimate the implications for BBN for a range of cosmologically interesting $\delta m^2$ values. The present paper improves on previous published work by taking into account the finite repopulation rate and the time dependence of the distortions to the neutrino momentum distributions. The treatment of chemical decoupling is also improved.