Cosmological Dependence of Sterile Neutrino Dark Matter With
  Self-Interacting Neutrinos
  Unexplored interactions of neutrinos could be the key to understanding the
nature of the dark matter (DM). In particular, active neutrinos with new
self-interactions can produce keV-mass sterile neutrinos that account for the
whole of the DM through the Dodelson-Widrow mechanism for a large range of
active-sterile mixing values. This production typically occurs before Big-Bang
Nucleosynthesis (BBN) in a yet uncharted era of the Universe. We assess how the
mixing range for keV-mass sterile neutrino DM is affected by the uncertainty in
the early Universe pre-BBN cosmology. This is particularly relevant for
identifying the viable parameter space of sterile neutrino searches allowed by
all astrophysical limits, as well as for cosmology, since the detection of a
sterile neutrino could constitute the first observation of a particle providing
information about the pre-BBN epoch. We find that the combined uncertainties in
the early Universe cosmology and neutrino interactions significantly expand the
allowed parameter space for sterile neutrinos that can constitute the whole of
the DM.
