Production of Sterile Neutrino Dark Matter and the 3.5 keV line

TL;DR

This paper investigates whether the 3.5 keV X-ray line could be a signal of sterile neutrino dark matter, and demonstrates how current astronomical data can distinguish its production mechanisms, favoring decay of heavy scalar singlets.

Contribution

It shows that present-day astronomical data can differentiate sterile neutrino production mechanisms, favoring decay of heavy scalar singlets as the source of the 3.5 keV line.

Findings

Lyman-alpha forest data constrains production mechanisms

Most mechanisms are disfavored except decay of heavy scalar singlets

Pinpointing the production mechanism informs dark matter detection

Abstract

The recent observation of an X-ray line at an energy of 3.5 keV mainly from galaxy clusters has initiated a discussion about whether we may have seen a possible dark matter signal. If confirmed, this signal could stem from a decaying sterile neutrino of a mass of 7.1 keV. Such a particle could make up all the dark matter, but it is not clear how it was produced in the early Universe. In this letter we show that it is possible to discriminate between different production mechanisms with present-day astronomical data. The most stringent constraint comes from the Lyman-{\alpha} forest and seems to disfavor all but one of the main production mechanisms proposed in the literature, which is the production via decay of heavy scalar singlets. Pinning down the production mechanism will help to decide whether the X-ray signal indeed comprises an indirect detection of dark matter.