Dark Matter Signatures in Cosmic Gamma-Rays

Abstract: This thesis concentrates on one of the indirect Dark Matter (DM) detection methods, namely through observations of Very High Energy (VHE) $\gamma$-ray signals from DM annihilation (or decay) in cosmic sources using the Imaging Atmospheric Cherenkov Technique (IACT). We discuss the particle physics and astrophysical aspects of those observations and perform several calculations which lead to an estimation of the DM detection prospects for IACTs. Using the DAMASCO code we calculate the photon flux from annihilating DM. We also calculate the so called astrophysical factors for two promising sources, namely the Galactic Center (GC) and the dwarf galaxy Segue 1. Based on those calculations we examine the prospects for DM detection with the MAGIC telescopes. We conclude that in the best case scenario, a boost factor of $\sim 240$ is needed for a 5$\sigma$ detection of the Galactic Center by the MAGIC telescopes during 100 hours of observation. A section is also devoted to the recent tentative measurements of a $\gamma$-ray line at $\sim 130$ GeV, for which we investigate the possibility that it might originate from DM decays. We conclude that such a line can be explained by an unstable particle with a decay time on the order of $10^{28}$ s, depending on the decay channel, the particle mass and the density distribution of the GC. If the decaying particle is a WIMP (Weakly Interacting Massive Particle), we expect a cut-off in the photon spectra at $E^\gamma \approx 260$ GeV. Thereafter, we apply this to a model for decaying gravitinos (supersymmetric partner of the graviton) and calculate a value for the relevant coupling. This model predicts a similar line in the neutrino spectrum which could be measured by the IceCube neutrino telescope.