Gamma-ray triangles: a possible signature of asymmetric dark matter in indirect searches

TL;DR

This paper proposes a novel gamma-ray spectral feature called gamma-ray triangle, arising from specific dark matter annihilation processes, and uses existing data to set bounds, highlighting potential for future detection in asymmetric dark matter models.

Contribution

Introduction of gamma-ray triangle as a new spectral signature of dark matter annihilation and analysis of its detectability with current and future gamma-ray telescopes.

Findings

No evidence of gamma-ray triangles in Fermi-LAT and H.E.S.S. data.

Strong upper bounds on dark matter annihilation cross section for this spectral feature.

Potential for upcoming telescopes to detect gamma-ray triangles in asymmetric dark matter models.

Abstract

We introduce a new type of gamma-ray spectral feature, which we denominate gamma-ray triangle. This spectral feature arises in scenarios where dark matter self-annihilates via a chiral interaction into two Dirac fermions, which subsequently decay in flight into another fermion and a photon. The resulting photon spectrum resembles a sharp triangle and can be readily searched for in the gamma-ray sky. Using data from the Fermi-LAT and H.E.S.S. instruments, we find no evidence for such spectral feature and therefore set strong upper bounds on the corresponding annihilation cross section. A concrete realization of a scenario yielding gamma-ray triangles consists of an asymmetric dark matter model where the dark matter particle carries lepton number. We show explicitly that this class of models can lead to intense gamma-ray spectral features, potentially at the reach of upcoming gamma-ray telescopes, opening a new window to explore asymmetric dark matter through indirect searches.