A closer look at the seesaw-dark matter correspondence

In an earlier work, we showed that in very simple neutrino portal-like extensions of the Standard Model it is possible to achieve a one-to-one correspondence between dark matter physics and the seesaw parameters controlling the genesis of neutrino masses. Notably, this can occur both when the dark matter is produced via freeze-in and relativistic freeze-out. In this article, we carry out a detailed phenomenological study of such scenarios. Specifically, we find the allowed regions for the neutrino portal coupling within which the correspondence is valid. We further constrain the parameter space from various observational and theoretical considerations. Within this, we derive the distribution function of a doubly frozen-in particle in order to more accurately compute its free-streaming horizon.