Anticipating the XRISM search for the decay of resonantly produced sterile neutrino dark matter

Abstract

ABSTRACT The sterile neutrino (N1) features in multiple extensions of the standard model and is a compelling dark matter candidate, especially as the decay of N1 with mass ms = 7.1 keV is a possible source for the unexplained 3.55 keV X-ray line reported in galaxy clusters. This particle will be accessible to the XRISM X-ray mission over the next 12 months. We revisit the physics behind N1 and the uncertainty in its parameters. We compare predictions for the ms = 7.1 keV N1 mixing angle, $\sin ^{2}(2\theta)\,$, and half-mode mass, Mhm, as described in the neutrino minimal standard model (νMSM) extension to existing X-ray observations and structure formation constraints. The strongest available constraints rule out N1 as a dark matter candidate, and a more optimistic reading of the data prefers $\sin ^{2}(2\theta)\,$ = 5 × 10−11 and Mhm = 3.5 × 108  ${\, \rm M_\odot }$. We highlight that the most promising upcoming opportunity for a detection is to find a line of velocity dispersion ∼500 $\, {\rm km}\, {\rm s}^{-1}$ in the Virgo cluster with XRISM, and then draw up a list of future objects of study to determine: (i) whether the line is from dark matter generally, and (ii) if from dark matter, whether that candidate is indeed N1.