Resonant production of light sterile neutrinos in compact binary merger remnants

The existence of eV-mass sterile neutrinos is not ruled out because of persistent experimental anomalies. Upcoming multimessenger detections of neutron-star merger remnants could provide indirect constraints on the existence of these particles. We explore the active-sterile flavor conversion phenomenology in a two-flavor scenario (one active plus one sterile species) as a function of the sterile neutrino mixing parameters, the neutrino emission angle from the accretion torus, and the temporal evolution of the merger remnant. The torus geometry and the neutron richness of the remnant are responsible for the occurrence of multiple resonant active-sterile conversions. The number of resonances strongly depends on the neutrino emission direction above or inside the remnant torus and leads to a large production of sterile neutrinos (and no antineutrinos) in the proximity of the polar axis, as well as more sterile antineutrinos than neutrinos in the equatorial region. As the black-hole torus evolves in time, the shallower baryon density is responsible for more adiabatic flavor conversion, leading to larger regions of the mass-mixing parameter space being affected by flavor mixing. Our findings imply that the production of sterile states could have indirect implications on the disk cooling rate, its outflows, and related electromagnetic observables which remain to be assessed.