Conservative upper limits on WIMP annihilation cross section from Fermi-LAT {\gamma}-rays

TL;DR

This paper derives conservative upper limits on dark matter annihilation cross sections using Fermi-LAT gamma-ray background data, considering various models and velocity-dependent annihilation scenarios, to constrain dark matter properties.

Contribution

It introduces new models for the extragalactic gamma-ray background and sets stringent upper limits on dark matter annihilation cross sections, including velocity-dependent cases.

Findings

Upper limits on annihilation cross section down to 10^-33 cm^3/s for DM < 100 GeV

Severe bounds on Sommerfeld enhancement effects

Constraints are conservative based on minimal dark matter models

Abstract

The spectrum of an isotropic extragalactic {\gamma}-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain stringent upper limits on their annihilation cross section. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, we consider models for DM annihilation depending on the inverse of the velocity and associate the EGBs to photons arising from the annihilation of DM in primordial halos. For DM velocities in protohalos of v ~ 10^-8 c, the annihilation cross section is constrained down to 10^-33 cm^3 /s for DM masses below 100 GeV. Given our choices for the EGB and the minimal DM modelling, the derived upper bounds are claimed to be conservative.