Primordial Black Holes, Hawking Radiation and the Early Universe

The 511 keV gamma emission from the galactic core may originate from a high concentration ($\sim {10}^{22}$) of primordial black holes (PBHs) in the core each of whose Hawking radiation includes $\sim {10}^{21}$ positrons per second. The PBHs we consider are taken as near the lightest with longevity greater than the age of the universe (mass $\sim {10}^{12}$ kg; Schwarzschild radius $\sim 1$ fm). These PBHs contribute only a small fraction of cold dark matter, ${\mathrm{\Omega }}_{PBH}\sim {10}^{-8}$. This speculative hypothesis, if confirmed implies the simultaneous discovery of Hawking radiation and an early universe phase transition.