Detecting Sterile Neutrino Dark Matter at MeV Gamma-Ray Observatories

TL;DR

This paper investigates how upcoming MeV gamma-ray observatories can detect sterile neutrino dark matter through its decay signals, proposing new analysis methods and including Sommerfeld enhancement effects for more accurate predictions.

Contribution

It introduces a novel analysis strategy in Compton data space and incorporates Sommerfeld enhancement in decay width calculations for the first time.

Findings

Both decay channels are experimentally accessible with upcoming observatories.

The 511 keV channel extends sensitivity up to around 100 MeV.

Combined detection of both signals offers a distinctive test for sterile neutrino dark matter.

Abstract

We explore the indirect detection of sterile neutrino dark matter within the gauged $U(1)_{B-L}$ extension of the Standard Model, in which three right-handed neutrinos account for neutrino masses, the baryon asymmetry, and dark matter. Focusing on the MeV mass range, we investigate two decay channels: the radiative decay $N \to \nu \gamma$, which produces a monochromatic photon, and the three-body decay $N \to e^- e^+ \nu$, which leads to a 511 keV photon signal from positronium decay. Taking the upcoming COSI mission as a case study, we show that both signals are experimentally accessible and complementary, with the 511 keV channel extending the sensitivity reach up to $O(100)$ MeV. We propose a novel analysis strategy in Compton data space to isolate the diffuse 511 keV emission. Furthermore, we incorporate, for the first time, the Sommerfeld enhancement in the decay width of $N \to e^- e^+ \nu$, enabling more accurate predictions of the signal near the kinematic threshold. The combined observation of both channels would provide a distinctive and testable signature of the sterile neutrino dark matter hypothesis.