Testing the Dark Matter Interpretation of the PAMELA Excess through Measurements of the Galactic Diffuse Emission

TL;DR

This paper proposes a method to test the dark matter interpretation of the PAMELA positron excess by analyzing the Galactic diffuse gamma-ray emission, aiming to distinguish dark matter signals from standard cosmic-ray contributions.

Contribution

It introduces a minimal-assumption analysis focusing on spatial and spectral features of gamma-ray emission to differentiate dark matter signals from cosmic-ray backgrounds.

Findings

DM-induced gamma-ray signals detectable above 100 GeV with Fermi

Standard cosmic-ray models can explain emissions if no DM excess is observed

Angular profiles can disentangle DM signals from astrophysical sources

Abstract

We propose to test the dark matter (DM) interpretation of the positron excess observed by the PAMELA cosmic-ray (CR) detector through the identification of a Galactic diffuse gamma-ray component associated to DM-induced prompt and radiative emission. The goal is to present an analysis based on minimal sets of assumptions and extrapolations with respect to locally testable or measurable quantities. We discuss the differences between the spatial and spectral features for the DM-induced components (with an extended, possibly spherical, source function) and those for the standard CR contribution (with sources confined within the stellar disc), and propose to focus on intermediate and large latitudes. We address the dependence of the signal to background ratio on the model adopted to describe the propagation of charged CRs in the Galaxy, and find that, in general, the DM-induced signal can be detected by the Fermi Gamma-ray Space Telescope at energies above 100 GeV. An observational result in agreement with the prediction from standard CR components only, would imply very strong constraints on the DM interpretation of the PAMELA excess. On the other hand, if an excess in the diffuse emission above 100 GeV is identified, the angular profile for such emission would allow for a clean disentanglement between the DM interpretation and astrophysical explanations proposed for the PAMELA excess. We also compare to the radiative diffuse emission at lower frequencies, sketching in particular the detection prospects at infrared frequencies with the Planck satellite.