Extending Fermi-LAT and H.E.S.S. Limits on Gamma-ray Lines from Dark Matter Annihilation

TL;DR

This paper develops a model-independent method to set limits on gamma-ray lines from dark matter annihilation using continuum gamma-ray spectra, extending constraints to higher dark matter masses beyond current telescope capabilities.

Contribution

It introduces a novel approach to constrain gamma-ray lines from dark matter by analyzing associated continuum spectra, applicable at masses beyond existing observational limits.

Findings

Extended limits on dark matter annihilation cross sections to gamma-ray lines beyond 500 GeV (Fermi-LAT) and 20 TeV (H.E.S.S.)

First constraints on gamma-ray lines from dark matter at very high masses

Demonstrated the utility of continuum gamma-ray spectra in probing dark matter signals

Abstract

Gamma-ray lines from dark matter annihilation ($\chi\chi\to \gamma X$, where $X=\gamma,h,Z$) are always accompanied, at lower energies, by a continuum gamma-ray spectrum stemming both from radiative corrections ($X=\gamma$) and from the decay debris of the second particle possibly present in the final state ($X=h,Z$). This model-independent gamma-ray emission can be exploited to derive novel limits on gamma-ray lines that do not rely on the line-feature. Although such limits are not expected to be as stringent, they can be used to probe the existence of $\gamma$-ray lines for dark matter masses beyond the largest energies accessible to current telescopes. Here, we use continuous gamma-ray searches from Fermi-LAT observations of Milky Way dwarf spheroidal galaxies and from H.E.S.S. observations of the Galactic Halo to extend the limits on the annihilation cross sections into monochromatic photons to dark matter masses well beyond $500$ GeV (Fermi-LAT) and $20$ TeV (H.E.S.S.). In this large mass regime, our results provide the first constraints on $\gamma$-ray lines from dark matter annihilation.