Production of Sterile Neutrino Dark Matter and the 3.5 keV line
  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.
