Bremsstrahlung gamma rays from light Dark Matter

TL;DR

This paper highlights the significant role of bremsstrahlung processes in gamma-ray signals from light Dark Matter annihilation, emphasizing their impact on the spectrum and the importance of accurate gas distribution modeling.

Contribution

It provides a detailed analysis of bremsstrahlung effects on gamma-ray spectra from light DM, showing their dominance in certain regions and the need for self-consistent modeling.

Findings

Bremsstrahlung can dominate gamma-ray emission in some Galactic regions.

Gamma-ray spectra are moderately sensitive to gas density variations.

Accurate modeling of gas distribution is crucial for interpreting DM signals.

Abstract

We discuss the often-neglected role of bremsstrahlung processes on the interstellar gas in computing indirect signatures of Dark Matter (DM) annihilation in the Galaxy, particularly for light DM candidates in the phenomenologically interesting O(10) GeV mass range. Especially from directions close to the Galactic Plane, the expected gamma-ray spectrum is altered via two effects: directly, by the photons emitted in the bremsstrahlung process on the interstellar gas by energetic electrons which are among the DM annihilation byproducts; indirectly, by the modification of the same electron spectrum, due to the additional energy loss process in the diffusion-loss equation (e.g. the resulting inverse Compton emission is altered). We quantify the importance of the bremsstrahlung emission in the GeV energy range, showing that it is the dominant component of the gamma-ray spectrum for some cases. We also find that, in regions in which bremsstrahlung dominates energy losses, the related gamma-ray emission is only moderately sensitive to possible large variations in the gas density. Still, we stress that, for computing precise spectra in the (sub-)GeV range, it is important to obtain a reliable description of the inner Galaxy gas distribution as well as to compute self-consistently the gamma emission and the solution to the diffusion-loss equation. For example, these are crucial issues to quantify and interpret meaningfully gamma-ray map `residuals' in terms of (light) DM annihilations.