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Exciting dark matter and the INTEGRAL/SPI 511 keV signal

Douglas P. Finkbeiner1 and Neal Weiner2

  • 1Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
  • 2Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, New York 10003, USA

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Phys. Rev. D 76, 083519 – Published 22 October, 2007

DOI: https://doi.org/10.1103/PhysRevD.76.083519

Abstract

We propose a dark matter candidate with an “excited state” 1–2 MeV above the ground state, which may be collisionally excited and deexcites 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 the International Gamma-Ray Astrophysics Laboratory/SPI in the inner Milky Way. Only a small fraction of the dark matter candidates 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 ∼3×1042 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.

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Phys. Rev. D 76, 083519– Published 22 October, 2007
  • Received 6 March 2007

© 2007 American Physical Society

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