Seesaw determination of the dark matter relic density

In this article, we show that in the usual type-I seesaw framework, augmented solely by a neutrino portal interaction, the dark matter (DM) relic density can be created through freeze-in in a manner fully determined by the seesaw interactions and the DM particle mass. This simple freeze-in scenario, where dark matter is not a seesaw state, proceeds through slow, seesaw-induced decays of Higgs, $W$ and $Z$ bosons. We identify two scenarios, one of which predicts the existence of an observable neutrino line.