Production of keV Sterile Neutrinos in Supernovae: New Constraints and Gamma Ray Observables

TL;DR

This paper investigates how keV--MeV sterile neutrinos can be produced in supernovae, deriving new constraints on their properties and predicting gamma-ray signals, with implications for dark matter and astrophysical observations.

Contribution

It demonstrates that supernovae can produce sterile neutrinos via MSW resonance, leading to stronger constraints on their mixing angles than previous X-ray limits, especially in the keV--MeV mass range.

Findings

Supernovae can produce sterile neutrinos with enhanced flux via MSW resonance.

New constraints on sterile neutrino mixing angles reach down to ~10^{-14}.

Gamma-ray signals from sterile neutrino decay are too faint for current detection.

Abstract

We study the production of sterile neutrinos in supernovae, focusing in particular on the keV--MeV mass range, which is the most interesting range if sterile neutrinos are to account for the dark matter in the Universe. Focusing on the simplest scenario in which sterile neutrinos mixes only with muon or tau neutrino, we argue that the production of keV--MeV sterile neutrinos can be strongly enhanced by a Mikheyev--Smirnov--Wolfenstein (MSW) resonance, so that a substantial flux is expected to emerge from a supernova, even if vacuum mixing angles between active and sterile neutrinos are tiny. Using energetics arguments, this yields limits on the sterile neutrino parameter space that reach down to mixing angles of the order of $\sin^2 2\theta \lesssim 10^{-14}$ and are up to an order of magnitude stronger than those from X-ray observations. While supernova limits suffer from larger systematic uncertainties than X-ray limits they apply also to scenarios in which sterile neutrinos are not abundantly produced in the early Universe. We also compute the flux of $\mathcal{O}(\text{MeV})$ photons expected from the decay of sterile neutrinos produced in supernovae, but find that it is beyond current observational reach even for a nearby supernova.