Extragalactic Gamma-Ray Background Limits on Evaporating Primordial Black Holes

Holes near the survival mass are shining today, faintly and in gamma rays, and the summed glow of a cosmological population of them would appear as a contribution to the extragalactic gamma-ray background. That background is measured, most precisely by the Fermi Large Area Telescope, and its smoothness is unforgiving: any population of evaporating holes numerous enough to matter as dark matter near the survival mass would overbrighten the background, particularly around a hundred megaelectronvolts where the emission of a survival-mass hole peaks and the measured background is comparatively low. The headline computed values are: f max at Mstar = 2.53e-09; T at Mstar MeV = 21.15. This is a simulated and computed study, not a measurement; the code and outputs are deposited alongside the text.