Constraints on the Galactic Halo Dark Matter from Fermi-LAT Diffuse Measurements

TL;DR

This study uses Fermi-LAT gamma-ray data to set constraints on dark matter properties in the Milky Way Halo, considering both direct and secondary gamma-ray production, and accounting for astrophysical uncertainties.

Contribution

It provides new limits on dark matter annihilation and decay by analyzing diffuse gamma-ray emission with advanced modeling of astrophysical backgrounds and cosmic-ray propagation.

Findings

Constraints challenge dark matter explanations for cosmic ray anomalies.

Limits exclude certain dark matter particle masses compatible with thermal production.

Modeling uncertainties significantly affect the derived dark matter constraints.

Abstract

We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope in the Milky Way Halo region searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+e- produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.