Note on Thermalization of Non-resonantly Produced Sterile Neutrinos

TL;DR

This paper analytically examines the conditions under which sterile neutrinos produced via non-resonant oscillations thermalize, concluding that such thermalization occurs only in parameter regions already excluded by existing limits, leaving allowed regions unaffected.

Contribution

It provides an analytic analysis of sterile neutrino thermalization, clarifying that thermalization occurs only in parameter regions already ruled out by other constraints.

Findings

Thermalization occurs only in large mixing angle regions already excluded.

Allowed sterile neutrino parameter space remains unaffected by thermalization.

Analytic approach clarifies the impact of cosmological conditions on sterile neutrino production.

Abstract

Using an analytic treatment, we discuss the parameter regions of large active-sterile neutrino mixing angles where sterile neutrinos produced in non-resonant flavour oscillations can approach thermalization in several cosmologies. We show that thermalization affects only large active-sterile neutrino mixing already rejected by different limits. Hence, the allowed sterile neutrino parameter regions are unaffected.