Title: Thermalizing sterile neutrino dark matter,
Abstract: Sterile neutrinos produced through oscillations are a well motivated dark
matter candidate, but recent constraints from observations have ruled out most
of the parameter space. We analyze the impact of new interactions on the
evolution of keV sterile neutrino dark matter in the early Universe. Based on
general considerations we find a mechanism which thermalizes the sterile
neutrinos after an initial production by oscillations. The thermalization of
sterile neutrinos is accompanied by dark entropy production which increases the
yield of dark matter and leads to a lower characteristic momentum. This
resolves the growing tensions with structure formation and X-ray observations
and even revives simple non-resonant production as a viable way to produce
sterile neutrino dark matter. We investigate the parameters required for the
realization of the thermalization mechanism in a representative model and find
that a simple estimate based on energy- and entropy conservation describes the
mechanism well.