@profumolight]).

The LAT instrument onboard Fermi is a tremendous tool for the indirect search for particle dark matter with gamma rays [@Baltz:2008wd; @ourgc]. Of special relevance for the present study, the flux of gamma rays from WIMP dark matter annihilation in clusters of galaxies has been shown to be in principle large enough to be detectable by Fermi-LAT [@Colafrancesco:2005ji; @ophiuchus]. Dark matter annihilation does not only produce gamma rays, but also additional stable particle species, such as energetic electrons and positrons. These, in turn, produce synchrotron, IC and bremsstrahlung radiation, with unique spectral features. The multi-wavelength emission from dark matter annihilation was studied in detail in [@gondolo; @bertone0101134; @aloisio0402588; @baltzwai; @coladraco; @xrdwarf; @ullioregis; @haze1; @haze2], and specifically in clusters of galaxies in [@Colafrancesco:2005ji; @ophiuchus; @colabullet]. Interestingly, it was demonstrated that if dark matter annihilation fuels to some appreciable degree either the radio emission in the Coma cluster [@Colafrancesco:2005ji], or the hard X-ray emission in the Ophiuchus cluster [@ophiuchus], Fermi is almost guaranteed to have the sensitivity to detect gamma rays from dark matter annihilation.

Upcoming gamma ray observations of clusters of galaxies have therefore profound implications for cosmology and, possibly, the discovery of New Physics. If Fermi detects gamma rays 