Constraining dark matter annihilation with the isotropic $\gamma$-ray background: updated limits and future potential

TL;DR

This paper updates limits on dark matter annihilation using the isotropic gamma-ray background, highlighting the importance of astrophysical uncertainties and the potential of future observations to constrain WIMP dark matter models.

Contribution

It provides an updated analysis of dark matter constraints from the IGRB, incorporating new astrophysical components like misaligned AGN and emphasizing future potential with reduced uncertainties.

Findings

Galactic and extragalactic gamma-ray sources significantly impact dark matter constraints.

Current uncertainties limit the ability to exclude certain WIMP masses.

Future reductions in uncertainties could severely constrain WIMP dark matter candidates up to several TeV.

Abstract

The nature of the Isotropic $\gamma$-ray Background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi $\gamma$-ray space Telescope ({\it Fermi}) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic milli-second pulsars. A recent prediction of the diffuse $\gamma$-ray emission from Active Galactic Nuclei (AGN) with a large viewing angle with respect to the line-of-sight (l.o.s.) has demonstrated that this faint but numerous population is also expected to contribute significantly to the total IGRB intensity. A more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMPs) into $\gamma$-rays. In this work, we evaluate the room left for galactic DM at high latitudes ($>10^\circ$) by including photons from both prompt emission and inverse Compton scattering, emphasizing the impact of the newly discovered contribution from misaligned AGN (MAGN) for such an analysis. Summing up all significant galactic and extragalactic components of the IGRB, we find that an improved understanding of the associated astrophysical uncertainties is still mandatory to put stringent bounds on thermally produced DM. On the other hand, we also demonstrate that the IGRB has the potential to be one of the most competitive {\it future} ways to test the DM WIMP hypothesis, once the present uncertainties are even slightly reduced. In fact, if MAGN contribute even at 90% of the maximal level consistent with our current understanding, thermally produced WIMPs would be severely constrained as DM candidates for masses up to several TeV.