Sterile neutrino dark matter production in presence of nonstandard neutrino self-interactions: An EFT approach

Sterile neutrinos with keV-scale masses are popular candidates for warm dark matter. In the most straightforward case, they are produced via oscillations with active neutrinos. We introduce effective selfinteractions of active neutrinos and investigate the effect on the parameter space of sterile neutrino mass and mixing. Our focus is on mixing with electron neutrinos, which is subject to constraints from several upcoming or running experiments like TRISTAN, ECHo, BeEST, and HUNTER. Depending on the size of the self-interaction, the parameter space moves closer to, or further away from, the one testable by those future experiments. In particular, we show that phase 3 of the HUNTER experiment would test a larger amount of parameter space in the presence of self-interactions than without them. We also investigate the effect of the self-interactions on the free-streaming length of the sterile neutrino dark matter, which is important for structure formation observables.