MeV Dark Matter: Has It Been Detected?

We discuss the possibility that the recent detection of 511 keV $\gamma$ rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass ($1–100\mathrm{MeV}$) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.

Figure 1

The angular distribution of $\gamma$ rays from DM annihilation averaged over the $2°$ angular resolution of the SPI spectrometer on INTEGRAL for several halo profiles. SPI’s observation indicates a full width at half maximum of $9°$ with a $6°–18°$ $2\sigma$ confidence interval. Shown as vertical dashed and dotted lines are the central value and $2\sigma$ limits of the angular widths found by SPI. To agree with these data, a halo model with $\gamma \sim 0.4–0.8$ is favored.