Multiple Populations of Same Sterile Neutrino as Dark Matter

TL;DR

This paper demonstrates that sterile neutrinos can have multiple populations with distinct momentum spectra from various production mechanisms, impacting dark matter models and their observational signatures.

Contribution

It introduces the concept of multi-modal relic spectra for sterile neutrinos arising from diverse early Universe production scenarios.

Findings

Multiple population components can coexist in sterile neutrino dark matter.

Different production mechanisms lead to colder and hotter populations.

Potential implications for dark matter detection and cosmological observations.

Abstract

Sterile neutrinos produced in the early Universe that mix with active neutrinos of the Standard Model are typically considered to consist of a single population resulting from one dominant production mechanism. We show that the same sterile neutrino species can naturally emerge with multiple population components, yielding a multi-modal relic momentum spectrum. We consider this with four distinct production scenarios: active-sterile non-resonant oscillations following resonant oscillations in the presence of a primordial lepton asymmetry, gravitational production through sterile neutrinogenesis from populations of evaporating primordial black holes, and heavy singlet Higgs or inflaton decays combined with non-resonant active-sterile oscillations or neutrinogenesis. We identify sterile neutrino mass ranges where a colder and a hotter population can be present with similar contributions and can also contribute non-negligibly to the dark matter relic abundance. We discuss some potential consequences of such a multi-population framework.