We consider possible mechanisms via which electroweak scale WIMPs χ0 could provide the source of the INTEGRAL/SPI 511 keV photon flux from the galactic centre. We consider scenarios where the WIMP spectrum contains near-degeneracies, with MeV-scale splitting, and focus on three possible production mechanisms for galactic positrons: (i) collisional excitation of the WIMP to a nearby charged state, χ0 + χ0 → χ+ + χ-, with the subsequent decay producing positrons; (ii) capture of the WIMP by nuclei in the galactic interstellar medium, χ0 + N → e+ + (χ- N); and (iii) the decay of a nearby long-lived state surviving from the big bang, χ20 → χ10 + e+ + e-. We find that process (i) requires a cross section which is significantly larger than the unitarity bound, process (ii) is allowed by unitarity, but is impractical due to terrestrial bounds on the χN cross section, while process (iii) is viable and we construct a simple model realization with singlet dark matter fields interacting with the Standard Model via the Higgs sector.
|Original language||English (US)|
|Number of pages||8|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Jul 26 2007|
Bibliographical noteFunding Information:
We would like to thank S. Ellison, J. Navarro, D. Vandenberg, M. Voloshin, and N. Weiner for helpful discussions and/or correspondence. The work of M.P. and A.R. was supported in part by NSERC, Canada. M.P. acknowledges the hospitality of the Aspen Center for Physics during the summer of 2006 while this work was in gestation. Research at the Perimeter Institute is supported in part by the Government of Canada through NSERC and by the Province of Ontario through MEDT.