Heavy sterile neutrino emission in core-collapse supernovae: Constraints and signatures

TL;DR

This paper investigates how heavy sterile neutrinos produced in supernovae affect energy loss and neutrino signals, setting constraints on their mixing angles and predicting detectable high-energy neutrino signatures.

Contribution

It provides new bounds on active-sterile neutrino mixing angles from supernova observations and predicts observable neutrino flux signatures in large detectors.

Findings

Active-sterile mixing angle constrained to .5 e-7 to avoid excessive energy loss.

Decay of sterile neutrinos can produce detectable high-energy neutrino flux.

Potential detection of a high-energy neutrino bump in future Galactic supernovae.

Abstract

Heavy sterile neutrinos with masses ${\mathcal O}(100)$ MeV mixing with active neutrinos can be produced in the core of a collapsing supernova (SN). In order to avoid an excessive energy loss, shortening the observed duration of the SN 1987A neutrino burst, we show that the active-sterile neutrino mixing angle should satisfy $\sin^2 \theta \lesssim 5 \times 10^{-7}$. For a mixing with tau flavour, this bound is much stronger than the ones from laboratory searches. Moreover, we show that in the viable parameter space the decay of such "heavy" sterile neutrinos in the SN envelope would lead to a very energetic flux of daughter active neutrinos; if not too far below current limits, this would be detectable in large underground neutrino observatories, like Super-Kamiokande, as a (slightly time-delayed) high-energy bump in the spectrum of a forthcoming Galactic SN event.