keV Sterile Neutrino Dark Matter from Singlet Scalar Decays: The Most General Case

TL;DR

This paper provides a comprehensive analysis of sterile neutrino dark matter production via singlet scalar decays, accounting for full momentum distributions and structure formation constraints, improving upon previous simplified models.

Contribution

It introduces a detailed, non-thermal momentum distribution approach to study sterile neutrino production, surpassing prior simplified density-based analyses.

Findings

Full momentum distribution calculations enable accurate structure formation constraints.

The study demonstrates the importance of non-thermal effects in dark matter production.

It establishes the most detailed framework for sterile neutrino dark matter from scalar decays.

Abstract

We investigate the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars. All previous studies applied simplifying assumptions and/or studied the process only on the level of number densities, which makes it impossible to give statements about cosmic structure formation. We overcome these issues by dropping all simplifying assumptions (except for one we showed earlier to work perfectly) and by computing the full course of Dark Matter production on the level of non-thermal momentum distribution functions. We are thus in the position to study all aspects of the resulting settings and apply all relevant bounds in a reliable manner. We have a particular focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free-streaming horizon clearly fails for highly non-thermal distributions. Our work comprises the most detailed and comprehensive study of sterile neutrino Dark Matter production by scalar decays presented so far.