Dark Matter Annihilation in the light of EGRET, HEAT, WMAP, INTEGRAL and ROSAT

TL;DR

This paper presents an anisotropic cosmic ray transport model consistent with multiple galactic observations, explaining positron fractions and gamma-ray excesses without invoking dark matter, and highlighting the importance of anisotropic diffusion and galactic winds.

Contribution

Introduction of an anisotropic convection driven transport model (aCDM) that aligns with galactic wind observations and explains cosmic ray and gamma-ray data without dark matter.

Findings

aCDM explains positron fraction increase observed by PAMELA and HEAT.

aCDM accounts for the absence of positron annihilation signals from molecular clouds.

EGRET gamma-ray excess cannot be explained by astrophysical effects in this model, supporting dark matter interpretation.

Abstract

The ROSAT Galactic wind observations confirm that our Galaxy launches supernova driven Galactic winds with wind speeds of about 150 km/s in the Galactic plane. Galactic winds of this strength are incompatible with current isotropic models for Cosmic Ray transport. In order to reproduce our local CRs in the presence of Galactic winds, charged CRs are required to be much more localized than in the standard isotropic GALPROP models. This requires that anisotropic diffusion is the dominant diffusion mode in the interstellar medium, particularly that the diffusion in the disk and in the halo are different. In addition small scale phenomena such as trapping by molecular cloud complexes and the structure of our local environment might influence the secondary CR production rate and our local CR density gradients. We introduce an anisotropic convection driven transport model (aCDM) which is consistent with the Galactic wind observations by ROSAT. This also explains the large bulge/disk ratio as observed by INTEGRAL. Furthermore such models predict an increase in the $e^+/(e^++e^-)$-fraction as observed by PAMELA and HEAT, if the synchrotron constraints in the 408 MHz and WMAP range are taken into account. No additional contribution from Dark Matter is required. The aCDM is able to explain the absence of a positron annihilation signal from molecular clouds as observed by INTEGRAL by virtue of a mechanism which confines and isotropizes CRs between MCs. We find that the EGRET excess of diffuse $\gamma$-rays currently cannot be explained by astrophysical effects in this type of model and that the interpretation of the EGRET excess as Dark Matter annihilation is perfectly consistent with all observational constraints from local CR fluxes and synchrotron radiation.