Dark Matter from Freeze-In via the Neutrino Portal

We investigate a minimal neutrino portal dark matter model (DM) 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 $\mathcal{O} \left( \mathrm{TeV} \right)$ heavy neutrinos. For a non-resonant production of DM we can predict the heavy neutrino mass to be $M_N \approx 10 \, \mathrm{TeV}$ and achieve a lower bound on the DM mass of $m_\chi \gtrsim 5 \, \mathrm{TeV}$. For the resonant production of DM, we find that it can be produced via freeze-in or freeze-out even with couplings of $\mathcal{O} \left( 10^{-5} \right)$. In the latter case to produce the observed for DM density we find $m_\chi \approx 100 \, \mathrm{eV}$.