Neutralino annihilation into γ rays in the Milky Way and in external galaxies

We discuss the gamma-ray signal from dark matter annihilation in our Galaxy and in external objects, namely, the Large Magellanic Cloud, the Andromeda Galaxy (M31), and M87. We derive predictions for the fluxes in a low energy realization of the minimal supersymmetric standard model and compare them with current data from EGRET, CANGAROO-II, and HEGRA and with the capabilities of new-generation satellite-borne experiments, like GLAST, and ground-based Cerenkov telescopes, like VERITAS. We find fluxes below the level required to explain the possible indications of a γ-ray excess shown by CANGAROO-II (toward the galactic center) and HEGRA (from M87). As far as future experiments are concerned, we show that only the signal from the galactic center could be accessible to both satellite-borne experiments and to atmospheric Cerenkov telescopes (ACTs), even though this requires very steep dark matter density profiles