A testable hidden-sector model for Dark Matter and neutrino masses
  We consider a minimal extension of the Standard Model with a hidden sector
charged under a dark local $U(1)'$ gauge group, accounting simultaneously for
light neutrino masses and the observed Dark Matter relic abundance. The model
contains two copies of right-handed neutrinos which give rise to light
neutrino-masses via an extended seesaw mechanism. The presence of a stable
Dark-Matter candidate and a massless state naturally arise by requiring the
simplest anomaly-free particle content without introducing any extra
symmetries. We investigate the phenomenology of the hidden sector considering
the $U(1)'$ breaking scale of the order of the electroweak scale. Confronting
the thermal history of this hidden-sector model with existing and future
constraints from collider, direct and indirect detection experiments provides
various possibilities of probing the model in complementary ways as every
particle of the dark sector plays a specific cosmological role. Across the
identified viable parameter space, a large region predicts a sizable
contribution to the effective relativistic degrees-of-freedom in the early
Universe that allows to alleviate the recently reported tension between late
and early measurements of the Hubble constant.
