Relic density of neutrinos with primordial asymmetries

TL;DR

This paper investigates how primordial neutrino asymmetries and flavor oscillations in the early universe affect neutrino equilibration and the resulting cosmological implications, including potential signals in precision data.

Contribution

It introduces a comprehensive kinetic model including collisions and pair processes to analyze flavor and kinetic equilibration among neutrinos and with the plasma.

Findings

BBN bound on nue-antinue asymmetry generally applies to all flavors

Fine-tuned initial asymmetries can lead to large neutrino excess radiation

Neutrino asymmetries may influence cosmological observations

Abstract

We study flavor oscillations in the early universe, assuming primordial neutrino-antineutrino asymmetries. Including collisions and pair processes in the kinetic equations, we not only estimate the degree of flavor equilibration, but for the first time also kinetic equilibration among neutrinos and with the ambient plasma. Typically the restrictive BBN bound on the nue-antinue asymmetry indeed applies to all flavors as claimed in the previous literature, but fine-tuned initial asymmetries always allow for a large surviving neutrino excess radiation that may show up in precision cosmological data.