Speaker
Description
In the Standard Model a Dark Matter candidate is missing, but it is relatively
simple to enlarge the model including one or more suitable particles.
We consider in this paper one such extension, inspired by simplicity and
by the goal to solve more than just the Dark Matter issue.
Indeed we consider a local $U(1) $ extension of the SM providing an
axion particle to solve the strong CP problem and including RH neutrinos
with appropriate mass terms. One of the latter is decoupled from the SM
leptons and can constitute stable sterile neutrino DM.
In this setting, the PQ symmetry arises only as an accidental symmetry
but its breaking by higher order operators is sufficiently suppressed to
avoid introducing a large $ \theta $ contribution.
The axion decay constant and the RH neutrino masses are related
to the same v.e.v.s and the PQ scale and both DM densities are determined by
the parameters of the axion and scalar sector.
The model predicts in general a mixed Dark Matter
scenario with both axion and sterile neutrino DM and is characterised by
a reduced density and observational signals from each single component.
