The 511 keV Excess and Primordial Black Holes
  An excess of 511 keV photons has been detected from the central region of the
Milky Way. It has been suggested that the positrons responsible for this signal
could be produced through the Hawking evaporation of primordial black holes.
After evaluating the constraints from INTEGRAL, COMPTEL, and Voyager 1, we find
that black holes in mass range of $\sim(1-4)\times10^{16}$ g could potentially
produce this signal if they make up a small fraction of the total dark matter
density. Proposed MeV-scale gamma-ray telescopes such as AMEGO or e-ASTROGAM
should be able to test this class of scenarios by measuring the diffuse gamma
ray emission from the Milky Way's inner halo.
