We analyze the indirect astrophysical signatures of secluded models of WIMP dark matter, characterized by a weak-scale rate for annihilation into light MeV-scale mediators which are metastable to decay into Standard Model states. Such scenarios allow a significant enhancement of the annihilation cross section in the galactic halo relative to its value at freeze-out, particularly when the mediator is light enough for this process to proceed through radiative capture to a metastable 'WIMP-onium' bound state. For MeV-scale vector mediators charged under a hidden U (1)′ gauge group, the enhanced annihilation rate leads predominantly to a sizable excess positron flux, even in the absence of astrophysical boost factors.
|Original language||English (US)|
|Number of pages||7|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Jan 26 2009|
Bibliographical noteFunding Information:
We would like to thank Misha Voloshin for numerous illuminating discussions on the subjects pertinent to this Letter. The work of M.P. and A.R. was supported in part by NSERC, Canada. Research at the Perimeter Institute is also supported in part by the Government of Canada through NSERC and by the Province of Ontario through MEDT.