Indirect Dark Matter Signals from EGRET and PAMELA compared

TL;DR

This paper compares gamma-ray and antimatter signals from dark matter annihilation, highlighting the impact of Galactic propagation models, especially convection, on interpreting PAMELA and EGRET data, and finds that DMA can explain antiprotons but not the positron excess.

Contribution

It demonstrates that anisotropic propagation models with convection are necessary to interpret cosmic ray data and shows that dark matter annihilation can account for antiproton excess but not the positron rise observed by PAMELA.

Findings

EGRET gamma-ray excess consistent with DMA

Convection affects charged particle yields significantly

DMA explains antiproton excess but not positron rise

Abstract

Dark Matter annihilation (DMA) may yield an excess of gamma rays and antimatter particles, like antiprotons and positrons, above the background from cosmic ray interactions. The excess of diffuse Galactic Gamma Rays from EGRET shows all the features expected from DMA. The new precise measurements of the antiproton and positron fractions from PAMELA are compared with the EGRET excess. It is shown that the charged particles are strongly dependent on the propagation model used. The usual propagation models with isotropic propagation models are incompatible with the recently observed convection in our Galaxy. Convection leads to an order of magnitude uncertainty in the yield of charged particles from DMA, since even a rather small convection will let drift the charged particles in the halo to outer space. It is shown that such anisotropic propagation models including convection prefer a contribution from DMA for the antiprotons, but the rise in the positron fraction, as observed by PAMELA, is incompatible with DMA, if compared with the EGRET excess. A rise in the positron/electron ratio is expected, if the observed rise in the proton/electron ratio is carefully fitted in a propagation model, although the rise is slightly larger than expected, so additional local sources may contribute as well within the limited accuracy of the data.