Exciting dark matter and the INTEGRAL/SPI 511 keV signal

By Douglas P. Finkbeiner, N. Weiner. 2007

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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{sup +}e{sup -} 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 {approx}3x10{sup 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{sup +}e{sup -} and freezes out with the correct relic density. We discuss possible observational consequences of this model.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6ead57405851078b34837c1a9d9e106e46c7411a

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Citations in the corpus

PRISM (Polarized Radiation Imaging and Spectroscopy Mission): an extended white paper (2013, background): “ture that can be distinguished from simple energy release [56,99] (see Fig.19). PRISM therefore provides an unprecedented probe of early-universe particle physics (e.g., dark matter in excited states [74,176] – 24 – Figure 17. Silk damping erases primordial anisotropies on small scales from the CMB,”
Higgs portal, fermionic dark matter, and a Standard Model like Higgs at 125 GeV (2012, background): “This situation is similar to secluded DM models [48], where DM annihilations into light mediator particles have been discussed, see also [49,50].”
A tale of tails: Dark matter interpretations of the Fermi GeV excess in light of background model systematics (2014, background): “The case in which a general mediator ϕ decays primarily to b quarks has already been discussed extensively in the literature [53 – 55 ,57 ,59 Here we consider eXciting dark matter models (XDM) [117,118].”
On possible interpretations of the high energy electron–positron spectrum measured by the Fermi Large Area Telescope (2009, background): “…of light intermediate scalar, pseudo-scalar or vector particles φ, subsequently decaying into light fermion (and possibly only e±) pairs (see e.g. Finkbeiner and Weiner 2007 [56], Pospelov et al. 2008 [57] and ArkaniHamed et al. 2008 [21]), produce a different spectrum from the monochromatic…”
Dark Matter Searches with Astroparticle Data (2011, background): “For example, light WIMPs (Hooper & Zurek, 2008) could annihilate to produce positrons, or WIMPs might upscatter to an excited state (Finkbeiner & Weiner, 2007) and then decay to produce the positrons.”
Probing dark forces and light hidden sectors at low-energy e+e- colliders (2009, background): “These mechanisms can also generate a splitting of O(MeV) to explain the INTEGRAL excess [15].”
The 511 keV emission from positron annihilation in the Galaxy (2010, background): “Finkbeiner and Weiner (2007) noticed that the velocity dispersion of DM particles in the gravitational potential of the inner Galaxy is of the order of a few 100 km s−1, endowing a 500 GeV WIMP with a kinetic energy >511 keV.”