Extragalactic Inverse Compton Light from Dark Matter Annihilation and the Pamela Positron Excess

TL;DR

This paper models the extragalactic inverse Compton emission from dark matter annihilation, analyzing how it depends on dark matter properties and structure formation, and compares predictions with observational data to constrain dark matter models.

Contribution

It provides a comprehensive calculation of extragalactic inverse Compton emission from dark matter annihilation across all redshifts and halos, highlighting constraints from X-ray and gamma-ray observations.

Findings

Low-mass dark matter models are constrained by X-ray data.

Gamma-ray observations limit models with high mass and annihilation rates.

Many models explaining the Pamela positron excess overproduce gamma-ray background.

Abstract

We calculate the extragalactic diffuse emission originating from the up-scattering of cosmic microwave photons by energetic electrons and positrons produced in particle dark matter annihilation events at all redshifts and in all halos. We outline the observational constraints on this emission and we study its dependence on both the particle dark matter model (including the particle mass and its dominant annihilation final state) and on assumptions on structure formation and on the density profile of halos. We find that for low-mass dark matter models, data in the X-ray band provide the most stringent constraints, while the gamma-ray energy range probes models featuring large masses and pair-annihilation rates, and a hard spectrum for the injected electrons and positrons. Specifically, we point out that the all-redshift, all-halo inverse Compton emission from many dark matter models that might provide an explanation to the anomalous positron fraction measured by the Pamela payload severely overproduces the observed extragalactic gamma-ray background.