Exciting Dark Matter and the INTEGRAL/SPI 511 keV signal
Abstract
We propose a WIMP candidate with an ``excited state'' 1-2 MeV above the ground state, which may be collisionally excited and de-excites by e+e- pair emission. By converting its kinetic energy into pairs, such a particle 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 have sufficient energy to excite, 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 ~3x10^42 pairs per second observed in the Galactic bulge. We specify the parameters of a pseudo-Dirac fermion designed to explain the positron signal, and find that it annihilates chiefly to e+e- and freezes out with the correct relic density. We discuss possible observational consequences of this model.
Cite
@article{arxiv.astro-ph/0702587,
title = {Exciting Dark Matter and the INTEGRAL/SPI 511 keV signal},
author = {Douglas P. Finkbeiner and Neal Weiner},
journal= {arXiv preprint arXiv:astro-ph/0702587},
year = {2008}
}
Comments
11 pages; v2 references added; v3 updated model to allow for single excitations and calculation of single excitation cross section; updated halo profiles; references added; conclusions unchanged