Overlaps at the Frontiers of
Astrophysics, Cosmology and Particle Physics

Cosmological constraints on the sum of the neutrino masses can be relaxed if the number density of active neutrinos is reduced compared to the standard scenario, while at the same time keeping the effective number of neutrino species $N_{\rm eff}\sim 3$ by introducing a new component of dark radiation. In this poster we present a UV model based on a U(1) symmetry in the dark sector, which can be either gauged or global, that realise this idea. It provides neutrino masses via the seesaw mechanism and, in addition to heavy seesaw neutrinos, we introduce O(10) generations of massless sterile neutrinos providing the dark radiation. Then we can accommodate active neutrino masses with $\sum m_{\nu}\sim1~$eV, in the sensitivity range of the KATRIN experiment. Finally we discuss the phenomenology of the model and identify the allowed parameter space.