Weakly-interacting massive particles (WIMPs) are the leading candidate for particle dark matter, and have been invoked to explain excess GeV gamma-rays, high-energy positrons, and even excess microwaves in the inner Milky Way. Until now, however, there has been no connection between these weak scale (mass of ~ 300 GeV) WIMPs and the 511 keV e+e- annihilation radiation from the inner Milky Way.
Neal Weiner and I have proposed a WIMP candidate with an "excited state" 1-2 MeV above the ground state (known as "exciting" dark matter, XDM). This state may be collisionally excited and decays by $e^+e^-$ pair emission. Such a particle converts WIMP kinetic energy into pairs, which in turn could produce a substantial fraction of the 511 keV line observed by INTEGRAL/SPI in the inner Milky Way. Only a small fraction of the WIMPs are above threshold, and that fraction drops sharply with Galactocentric radius, naturally yielding a radial cutoff, as observed. Even if the scattering probability in the inner kpc is << 1% per Hubble time, enough power is available to produce the number of pairs per second observed. I will specify the parameters required to explain the INTEGRAL result, and discuss other observational consequences of this model, including our recent consideration of BBN Lithium abundance.