Constraining the window on sterile neutrinos as warm dark matter

TL;DR

The paper addresses constraining sterile neutrinos as warm dark matter by incorporating their non-thermal momentum distribution into the mapping between particle mass and cosmological observables. It shows that the production temperature and resulting momentum distribution modify the small-scale power suppression, yielding a revised window of $2.6$ keV $< m < 5$ keV and emphasizing a spectral line search at $E = m/2$ from radiative decay. The transfer-function framework, including $T(k) = \left[ 1 + (\alpha k)^{2\nu} \right]^{-5/\nu}$ with $\nu=1.12$ and the mass–density parameter mappings between conventional WDM and sterile WDM, underpins the revised bounds. Decay constraints further restrict to $m<5$ keV, making the observational target a narrow spectral line while also outlining alternative DM scenarios if such signals are not detected.

Abstract

Sterile neutrinos may be one of the best Warm Dark Matter candidates we have today. Both lower and upper bounds on the mass of the sterile neutrino come from astronomical observations. We show that the proper inclusion of the neutrino momentum distribution reduces the allowed region to be 2.6 keV < m < 5 keV for the simplest models. A search for a spectral line with E=m/2 is thus more interesting than ever before.