Resonant Production of Light Sterile Neutrinos in Compact Binary Merger Remnants

TL;DR

This paper investigates how light sterile neutrinos could be produced in neutron-star merger remnants through active-sterile flavor conversions, with implications for astrophysical observations and constraints on sterile neutrino properties.

Contribution

It provides a detailed analysis of active-sterile neutrino conversion mechanisms in merger remnants, highlighting the dependence on geometry, density, and evolution, which was not thoroughly explored before.

Findings

Multiple resonant conversions occur depending on emission angle and remnant evolution.

Large sterile neutrino production occurs near the polar axis and in the equatorial region.

Flavor conversion effects influence disk cooling, outflows, and electromagnetic signals.

Abstract

The existence of eV-mass sterile neutrinos is not ruled out because of persistent experimental anomalies. Upcoming multi-messenger 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 (1 active + 1 sterile species) as a function of the sterile neutrino mixing parameters, neutrino emission angle from the accretion torus, and 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 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.