Electron-positron Annihilation Lines and Decaying Sterile Neutrinos

TL;DR

This paper explores how decaying sterile neutrinos could produce observable signals like positron annihilation lines and gamma-ray fluxes in the Milky Way, setting bounds on decay rates and predicting neutrino fluxes.

Contribution

It provides new astrophysical bounds on sterile neutrino decay rates and predicts observable gamma-ray and neutrino signals from their decays.

Findings

Bounds on sterile neutrino decay rate: ≥ 10^{-28} s^{-1}

Predicted gamma-ray flux from Milky Way center: 1.2×10^{-4} to 9.7×10^{-4} ph cm^{-2} s^{-1}

Estimated active neutrino flux: 0.02 to 0.1 cm^{-2} s^{-1}

Abstract

If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences. We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way center, and we thus obtain bounds on the sterile neutrino decay rate $\Gamma_e \ge 10^{-28}$ s$^{-1}$ from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of $1.2 \times 10^{-4}-9.7 \times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$ from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate the flux of active neutrinos produced by sterile neutrino decays to be $0.02-0.1$ cm$^{-2}$ s$^{-1}$ passing through the earth.