Opening up new parameter space for sterile neutrino dark matter

Sterile neutrinos are compelling dark matter (DM) candidates, yet the minimal production mechanism solely based on active-sterile ( ν a − ν s ) oscillations is robustly excluded by astrophysical observations. Nonstandard self-interactions in either the active ( ν a − ν a ) or sterile ( ν s − ν s ) sector are known to alter the sterile neutrino DM production in the early Universe, which could alleviate the tension with astrophysical constraints. Here, we propose a new solution where scalar-mediated nonstandard interactions between active and sterile neutrinos ( ν a − ν s ) lead to new production channels for sterile neutrino DM, independent of the active-sterile mixing and without the need for any fine-tuned resonance or primordial lepton asymmetries. This framework enables efficient sterile neutrino DM production even at vanishingly small mixing angles and opens up new viable regions of parameter space that can be tested with future x-ray and gamma-ray observations. It also provides a new mechanism for observable neutrino-DM interactions while being consistent with DM relic density and has broad phenomenological implications for astrophysical neutrinos and beyond.