γ-ray lines as a probe for a cold-dark-matter halo

Annihilations of cold dark matter via the reaction $\chi \overline{\chi }\to \gamma \gamma$ in the halo of our Galaxy produce monoenergetic $\gamma$ rays. The detection by satellite-borne detectors of a $\gamma$-ray line originating from the galactic halo would be a clear signature of particle dark matter, and could probe particles (such as photinos) that are difficult to detect by ground-based experiments. We show that the signal may be lost in the noise if there is a closure density of dark matter.