Constraining Primordial Black Hole Abundance with the Galactic 511 keV Line.
Models in which dark matter consists entirely of primordial black holes (PBHs) with masses around 10^{17}  g are currently unconstrained. However, if PBHs are a component of the Galactic dark matter density, they will inject a large flux of energetic particles into the Galaxy as they radiate. Positrons produced by these black holes will subsequently propagate throughout the Galaxy and annihilate, contributing to the Galactic 511 keV line. Using measurements of this line by the INTEGRAL satellite as a constraint on PBH positron injection, we place new limits on PBH abundance in the mass range 10^{16}-10^{17}  g, ruling out models in which these PBHs constitute the entirety of dark matter.