Diluted equilibrium sterile neutrino dark matter

TL;DR

This paper proposes a model where keV to MeV sterile neutrinos, produced via early Universe freeze-out and entropy dilution, can serve as cold dark matter without conflicting with current observational constraints.

Contribution

The work introduces a novel sterile neutrino dark matter production mechanism involving early freeze-out and entropy dilution, avoiding reliance on active-sterile mixing.

Findings

Sterile neutrinos can achieve correct relic density through entropy dilution.

The model allows sterile neutrinos to act as cold dark matter despite low rest masses.

Future observations could test or constrain the proposed scenario.

Abstract

We present a model where sterile neutrinos with rest masses in the range ~ keV to ~ MeV can be the dark matter and be consistent with all laboratory, cosmological, large-scale structure, as well as x-ray constraints. These sterile neutrinos are assumed to freeze out of thermal and chemical equilibrium with matter and radiation in the very early Universe, prior to an epoch of prodigious entropy generation ("dilution") from out-of-equilibrium decay of heavy particles. In this work, we consider heavy, entropy-producing particles in the ~ TeV to ~ EeV rest-mass range, possibly associated with new physics at high-energy scales. The process of dilution can give the sterile neutrinos the appropriate relic densities, but it also alters their energy spectra so that they could act like cold dark matter, despite relatively low rest masses as compared to conventional dark matter candidates. Moreover, since the model does not rely on active-sterile mixing for producing the relic density, the mixing angles can be small enough to evade current x-ray or lifetime constraints. Nevertheless, we discuss how future x-ray observations, future lepton number constraints, and future observations and sophisticated simulations of large-scale structure could, in conjunction, provide evidence for this model and/or constrain and probe its parameters.