Title: Roads for Right-handed Neutrino Dark Matter: Fast Expansion, Standard Freeze-out, and Early Matter Domination
Abstract: Right-handed neutrinos appear in several extensions beyond the
Standard Model, specially in connection to neutrino masses. Motivated by
this, we present a model of right-handed neutrino dark matter that
interacts with Standard Model particles through a new gauge symmetry as
well as via mass mixing between the new vector field and the Z boson,
and investigate different production mechanisms. We derive the dark
matter relic density when the Hubble rate is faster than usual, when
dark matter decouples in a matter domination epoch, and when it
decouples in a radiation domination regime, which is then followed by a
matter domination era. The direct detection rate features a
spin-independent but velocity suppressed operators, as well as a
spin-dependent operator when the mass mixing is correctly accounted for.
We put all these results into perspective with existing flavor physics,
atomic parity violation, and collider bounds. Lastly, we outline the
region of parameter space in which a weak scale right-handed neutrino
dark matter stands as a viable dark matter candidate.