Dark Matter from Freeze-In via the Neutrino Portal

TL;DR

This paper explores a minimal neutrino portal dark matter model where dark matter is produced via freeze-in, focusing on parameter space regions with small neutrino Yukawa couplings and analyzing the viability of different production mechanisms.

Contribution

It investigates freeze-in production of dark matter in a neutrino portal model, including resonant and non-resonant scenarios, and assesses observational constraints such as the Lyman-alpha forest.

Findings

Non-resonant production yields DM energy density independent of mass.

Resonant production can occur via freeze-in or freeze-out with small couplings.

Lyman-alpha forest constraints exclude feeble freeze-out, favoring resonant freeze-in for DM mass > 3 keV.

Abstract

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 $\mathcal{O} \left( \mathrm{TeV} \right)$ 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 $M_N \approx 10 \, \mathrm{TeV}$. For the resonant production of DM, we find that it can be produced via freeze-in or freeze-out even with couplings of $\mathcal{O} \left( 10^{-5} \right)$. However, the measurement of the Lyman-$\alpha$ forest rules out the feeble coupled freeze-out case completely, while the resonant freeze-in production is only viable for $m_{DM} \gtrsim 3 \, \mathring{keV}$.