  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.
