Fitting the Fermi-LAT GeV excess: on the importance of the propagation of electrons from dark matter

TL;DR

This paper emphasizes the importance of electron propagation effects, such as inverse Compton scattering and bremsstrahlung, in interpreting the Fermi-LAT GeV excess as potential dark matter signals, especially for leptonic annihilation channels.

Contribution

It demonstrates that including electron propagation effects significantly alters the dark matter interpretation of the gamma-ray excess.

Findings

Electron propagation impacts gamma-ray spectrum interpretation.

Leptonic annihilation channels are affected by diffusion and scattering.

Dark matter profile assumptions are less constrained without considering electron effects.

Abstract

An excess of gamma rays at GeV energies has been detected in the Fermi-LAT data. This signal comes from a narrow region around the Galactic Center and has been interpreted as possible evidence for light (30 GeV) dark matter particles. Focussing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding into b quarks, with a dark matter profile going as r^{-1.2}. We show that this is not the only possible annihilation set-up. More specifically, we show how including the contributions to the gamma-ray spectrum from inverse Compton scattering and bremsstrahlung from electrons produced in dark matter annihilations, and undergoing diffusion through the Galactic magnetic field, significantly affects the spectrum for leptonic final states. This drastically changes the interpretation of the excess in terms of dark matter.