Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-02-21
Phys.Rev.D76:083519,2007
Astronomy and Astrophysics
Astrophysics
11 pages; v2 references added; v3 updated model to allow for single excitations and calculation of single excitation cross sec
Scientific paper
10.1103/PhysRevD.76.083519
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.
Finkbeiner Douglas Paul
Weiner Neal
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