Cosmological Imprints of Frozen-In Light Sterile Neutrinos

TL;DR

This paper explores various cosmological scenarios involving sterile neutrino dark matter produced through the freeze-in mechanism, highlighting their potential observational signatures and compatibility with cosmological constraints.

Contribution

It provides a comprehensive analysis of different production mechanisms and their unique cosmological signatures, including effects on Neff and dark matter properties.

Findings

Sterile neutrinos can be cold, warm, or hot dark matter depending on production details.

Some scenarios predict detectable deviations in Neff during Big Bang nucleosynthesis.

The study identifies conditions under which sterile neutrinos remain compatible with cosmological observations.

Abstract

We investigate observable cosmological aspects of sterile neutrino dark matter produced via the freeze-in mechanism. The study is performed in a framework that admits many cosmologically interesting variations: high temperature production via annihilation processes from higher dimensional operators or low temperature production from decays of a scalar, with the decaying scalar in or out of equilibrium with the thermal bath, in supersymmetric or non-supersymmetric setups, thus allowing us to both extract generic properties and highlight features unique to particular variations. We find that while such sterile neutrinos are generally compatible with all cosmological constraints, interesting scenarios can arise where dark matter is cold, warm, or hot, has nontrivial momentum distributions, or provides contributions to the effective number of relativistic degrees of freedom Neff during Big Bang nucleosynthesis large enough to be probed by future measurements.