Improved determination of sterile neutrino dark matter spectrum

TL;DR

This paper refines the theoretical calculation of sterile neutrino dark matter abundance, especially in light of potential X-ray signals, by analyzing the spectrum and lepton asymmetry requirements for 7.1 keV sterile neutrinos.

Contribution

It provides an improved, detailed computation of the sterile neutrino spectrum and lepton asymmetry needed for correct dark matter abundance, considering various neutrino Yukawa structures and plasma effects.

Findings

Determines the lepton asymmetry for correct sterile neutrino abundance.

Estimates the non-equilibrium spectrum relevant for structure formation.

Accounts for charge neutrality and hadronic contributions in the calculations.

Abstract

The putative recent indication of an unidentified 3.55 keV X-ray line in certain astrophysical sources is taken as a motivation for an improved theoretical computation of the cosmological abundance of 7.1 keV sterile neutrinos. If the line is interpreted as resulting from the decay of Warm Dark Matter, the mass and mixing angle of the sterile neutrino are known. Our computation then permits for a determination of the lepton asymmetry that is needed for producing the correct abundance via the Shi-Fuller mechanism, as well as for an estimate of the non-equilibrium spectrum of the sterile neutrinos. The latter plays a role in structure formation simulations. Results are presented for different flavour structures of the neutrino Yukawa couplings and for different types of pre-existing lepton asymmetries, accounting properly for the charge neutrality of the plasma and incorporating approximately hadronic contributions.