Cosmic Ray-Dark Matter Scattering: a New Signature of (Asymmetric) Dark Matter in the Gamma Ray Sky

TL;DR

This paper explores a new gamma-ray signature from cosmic-ray scattering off dark matter, especially in asymmetric dark matter scenarios where traditional annihilation signals are absent, potentially detectable by Fermi-LAT.

Contribution

It introduces cosmic-ray scattering with final-state photon emission as a novel detection method for dark matter, focusing on asymmetric models where annihilation signals are suppressed.

Findings

Gamma-ray emission from cosmic-ray scattering can be detectable in some scenarios.

The flux and spectral features depend on dark matter properties and cosmic-ray flux.

Potential observability with Fermi-LAT in specific dark matter models.

Abstract

We consider the process of scattering of Galactic cosmic-ray electrons and protons off of dark matter with the radiation of a final-state photon. This process provides a novel way to search for Galactic dark matter with gamma rays. We argue that for a generic weakly interacting massive particle, barring effects such as co-annihilation or a velocity-dependent cross section, the gamma-ray emission from cosmic-ray scattering off of dark matter is typically smaller than that from dark matter pair-annihilation. However, if dark matter particles cannot pair-annihilate, as is the case for example in asymmetric dark matter scenarios, cosmic-ray scattering with final state photon emission provides a unique window to detect a signal from dark matter with gamma rays. We estimate the expected flux level and its spectral features for a generic supersymmetric setup, and we also discuss dipolar and luminous dark matter. We show that in some cases the gamma-ray emission might be large enough to be detectable with the Fermi Large Area Telescope.