Unveiling Dark Matter through Gamma Rays : Spectral Features, Spatial Signatures and Astrophysical Backgrounds

Abstract

Although the existence of Dark Matter (DM) is supported by multiple unrelated evidences at different scales, its intimate nature is far from been unveiled by current detection strategies. This thesis focuses on indirect searches of DM Weakly Interacting Massive Particles (WIMPs) through gamma-rays. In order to accurately model the spectral DM distribution, we perform the first fully general calculation of leading electroweak corrections to the annihilation rate of supersymmetric neutralino DM and we demonstrate that these corrections significantly enhance the total photon yield, partially because of contributions that have been overlooked so far. Besides spectral signatures, DM is expected to show distinctive spatial features because of DM subhalos of various sizes and masses hosted by the main galactic halo as predicted by N-body simulations. We compute the gamma-ray angular power spectrum of galactic DM by exploiting the results of recent N-body simulations. Notably, we emphasize the theoretical uncertainty associated to such a calculation which may turn out to be relevant for current DM searches by means of gamma-ray anisotropies. A good DM detection strategy should optimize methods and choice of targets. We demonstrate that traditional methods for gamma-ray line searches, which greatly reduce the uncertainties related to astrophysical background fluxes, can successfully be extended to look for any spectral feature at photon energies close to the DM particle mass and that projected constraints on the DM annihilation cross section by means of the next generation of Cherenkov telescopes turn out to be considerably improved with respect to current limits. Moreover, we prove the isotropic diffuse gamma-ray background (IGRB) to be one of the most promising targets for testing the WIMP hypothesis once the uncertainties on the unavoidable astrophysical background will be reduced by further data. We indeed show that the most important astrophysical contribution to the IGRB is due to the unresolved population of mis-aligned active galactic nuclei. Taking into account this additional contribution to the IGRB, thermally produced WIMPs may be severely constrained for masses up to several TeV.