the origin of radio halos [@dennison], the “cooling-flow” problem [@fabian] and particle acceleration within cluster merger shocks [@sarazin04].

Clusters of galaxies are potentially powerful observational probes of cosmology (see e.g. [@voit; @HMH01; @albrecht06]). In this context, the accurate understanding of non-thermal phenomena in clusters is crucial to their ultimate utility as cosmological probes. Specifically, the estimate of cluster masses, which is at the basis of all cosmological applications using clusters, frequently relies on the assumption of hydrostatic equilibrium between gravitational forces and the thermal pressure supplied by the ICM. The accuracy of hydrostatic mass determinations is therefore limited by our understanding of the non-thermal pressure provided by cosmic rays, turbulence and magnetic fields in the ICM [@ensslin97; @nagai2007]. The Fermi Gamma-Ray Space Telescope, as well as current and planned ground based atmospheric Cherenkov telescopes (ACTs) will be able to probe the energy density supplied by cosmic rays, and possibly the evolution with redshift of cosmic ray pressure, to an unprecedented level of accuracy [@pfrommer2004; @nagaiando].

A more exotic possibility for non-thermal activity in galaxy clusters was first envisioned by Totani in Ref. [@totani]: the pair annihilation of weakly interacting massive particles (WIMP) constituting the dark matter halo. Following that seminal 