Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background

TL;DR

This paper explores how dark matter annihilation could produce distinctive anisotropy patterns in the cosmic gamma-ray background, which could be detected by future gamma-ray observatories like GLAST, depending on the structure of dark matter on small scales.

Contribution

It introduces new anisotropy scenarios considering uncertainties in dark matter clustering and proposes cross-correlation methods as additional detection tools.

Findings

Dark matter anisotropy signatures are detectable if sub-galactic contributions are moderate.

Degeneracy between astrophysical and dark matter anisotropies occurs if sub-galactic structures dominate.

Cross-correlation techniques enhance the sensitivity to dark matter signatures.

Abstract

The extragalactic cosmic gamma-ray background (CGB) is an interesting channel to look for signatures of dark matter annihilation. In particular, besides the imprint in the energy spectrum, peculiar anisotropy patterns are expected compared to the case of a pure astrophysical origin of the CGB. We take into account the uncertainties in the dark matter clustering properties on sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark matter angular signature is achieved when the annihilation signal receives only a moderate contribution from sub-galactic clumps and/or cuspy haloes. Experimentally, if galactic foregrounds systematics are efficiently kept under control, the angular differences are detectable with the forthcoming GLAST observatory, provided that the annihilation signal contributes to the CGB for a fraction >10-20%. If, instead, sub-galactic structures have a more prominent role, the astrophysical and dark matter anisotropies become degenerate, correspondingly diluting the DM signature. As complementary observables we also introduce the cross-correlation between surveys of galaxies and the CGB and the cross-correlation between different energy bands of the CGB and we find that they provide a further sensitive tool to detect the dark matter angular signatures.