Dodelson-Widrow Production of Sterile Neutrino Dark Matter with Non-Trivial Initial Abundance

TL;DR

This paper develops a semi-analytic method to analyze the Dodelson-Widrow mechanism for sterile neutrino dark matter production with arbitrary initial conditions, assessing its interplay with other production mechanisms and implications for structure formation.

Contribution

It introduces a semi-analytic approach to evaluate the DW mechanism on arbitrary initial sterile neutrino abundances, improving upon previous additive spectrum assumptions.

Findings

Validated the semi-analytic method against numerical results.

Quantified the accuracy of spectrum addition approximation.

Explored the impact of DW on structure formation beyond free-streaming estimates.

Abstract

The simplest way to create sterile neutrinos in the early Universe is by their admixture to active neutrinos. However, this mechanism, connected to the Dark Matter (DM) problem by Dodelson and Widrow (DW), cannot simultaneously meet the relic abundance constraint as well as bounds from structure formation and X-rays. Nonetheless, unless a symmetry forces active-sterile mixing to vanish exactly, the DW mechanism will unavoidably affect the sterile neutrino DM population created by any other production mechanism. We present a semi-analytic approach to the DW mechanism acting on an arbitrary initial abundance of sterile neutrinos, allowing to combine DW with any other preceding production mechanism in a physical and precise way. While previous analyses usually assumed that the spectra produced by DW and another mechanism can simply be added, we use our semi-analytic results to discuss the validity of this assumption and to quantify its accurateness, thereby also scrutinising the DW spectrum and the derived mass bounds. We then map our results to the case of sterile neutrino DM from the decay of a real SM singlet coupled to the Higgs. Finally, we will investigate aspects of structure formation beyond the usual simple free-streaming estimates in order to judge on the effects of the DW modification on the sterile neutrino DM spectra generated by scalar decay.