Many scenarios have been proposed to explain the 511 keV line from the center of the galaxy in terms of a decaying/annihilating dark matter with lifetime larger than the age of the Universe. I will discuss an alternative scenario where a subdominant fraction of Dark matter decays to positrons, early on. The positrons cool down by scattering off the cosmic microwave background and eventually annihilate when they fall into Galactic potential wells. The resulting 511 keV flux not only places constraints on this class of models but might even be consistent with that observed by the INTEGRAL satellite.
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