Sterile neutrino hot, warm, and cold dark matter

TLDR

The study calculates the incoherent resonant and non‑resonant scattering production of sterile neutrinos in the early universe. The authors compute sterile neutrino production by incorporating matter effects (MSW resonance and quantum damping), finite‑temperature corrections, dilution from relativistic species annihilation, and scattering‑rate enhancements from high‑temperature particle‑antiparticle pairs. They identify ranges of sterile neutrino masses, mixing angles, and lepton numbers that allow the particles to serve as viable hot, warm, and cold dark matter candidates consistent with observational constraints.

Abstract

We calculate the incoherent resonant and non-resonant scattering production of sterile neutrinos in the early universe. We find ranges of sterile neutrino masses, vacuum mixing angles, and initial lepton numbers which allow these species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM) candidates which meet observational constraints. The constraints considered here include energy loss in core collapse supernovae, energy density limits at big bang nucleosynthesis, and those stemming from sterile neutrino decay: limits from observed cosmic microwave background anisotropies, diffuse extragalactic background radiation, and ${}^{6}\mathrm{L}\mathrm{i}/\mathrm{D}$ overproduction. Our calculations explicitly include matter effects, both effective mixing angle suppression and enhancement (MSW resonance), as well as quantum damping. We for the first time properly include all finite temperature effects, dilution resulting from the annihilation or disappearance of relativistic degrees of freedom, and the scattering-rate-enhancing effects of particle-antiparticle pairs (muons, tauons, quarks) at high temperature in the early universe.