Dark Matter from Freeze-In via the Neutrino Portal

We investigate a minimal neutrino portal dark matter (DM) model where a right-handed neutrino both generates the observed neutrino masses and mediates between the SM and the dark sector, which consists of a fermion and a boson. In contrast to earlier work, we explore regions of the parameter space where DM is produced via freeze-in instead of freeze-out motivated by the small neutrino Yukawa couplings in case of O(TeV) heavy neutrinos. For a non-resonant production of DM, its energy density is independent of the DM mass. Assuming a democratic coupling structure we find M_N > 10 TeV and achieve a lower bound on the DM mass > 5 TeV. For the resonant production of DM, we find that it can be produced via freeze-in or freeze-out even with couplings of O(10^-5).