Axion-Sterile-Neutrino Dark Matter
  Extending the Standard Model with three right-handed neutrinos and a simple
QCD axion sector can account for neutrino oscillations, dark matter and baryon
asymmetry; at the same time, it solves the strong CP problem, stabilizes the
electroweak vacuum and can implement critical Higgs inflation (satisfying all
current observational bounds). We perform here a general analysis of dark
matter (DM) in such a model, which we call the $a\nu$MSM. Although critical
Higgs inflation features a (quasi) inflection point of the inflaton potential
we show that DM cannot receive a contribution from primordial black holes in
the $a\nu$MSM. This leads to a multicomponent axion-sterile-neutrino DM and
allows us to relate the axion parameters, such as the axion decay constant, to
the neutrino parameters. We include several DM production mechanisms: the axion
production via misalignment and decay of topological defects as well as the
sterile-neutrino production through the resonant and non-resonant mechanisms
and in the recently proposed CPT-symmetric universe.
