Neutrino Self–Interactions in the Dodelson–Widrow Mechanism

Sterile neutrinos have long been accepted as minimal possible Standard Model extensions due to their sim- plicity and ability to generate low-mass active neutrinos through the Seesaw mechanism. Furthermore, due to its feeble interaction, the heavy neutrino mass eigenstate can remain cosmologically long-lived and avoid thermalization, making it an attractive dark matter candidate. Dodelson and Widrow showed how to pro- duce a sterile population compatible with the required dark matter energy density, but the necessary active- sterile mixing is ruled out by X-ray bounds on the radiative decay of the sterile neutrino. In order to explain dark matter using sterile neutrinos, one must thus provide for a mechanism that allows for the mixing angle to assume lower values. We reproduce the effect of sterile neutrino self-interactions mediated by a scalar on their production, and in agreement with the literature, we find that a part of the parameter space is not in tension with cosmological bounds for a small enough scalar mass. Then, as a new contribution to the liter- ature, we evaluate the effect of spin-1 boson mediated self-interactions on sterile neutrino production, and find that it is able to saturate the dark matter energy density requirement for even lower mixing angles.