Revisiting the constraints on primordial black hole abundance with the isotropic gamma-ray background
Siyu Chen, H. H. Zhang, Guang-Bo Long
Abstract
We revisit the constraints on primordial black holes (PBHs) in the mass range ${10}^{13}\text{ }\text{ }\mathrm{g}--{10}^{18}\text{ }\text{ }\mathrm{g}$ by comparing the 100 keV--5 GeV gamma-ray background with isotropic flux from PBH Hawking radiation (HR). We investigate three effects that may update the constraints on the PBH abundance; (i) reliably calculating the secondary spectra of HR for energy below 5 GeV, (ii) the contributions to the measured isotropic flux from the Galactic PBH HR and that from annihilation radiation due to evaporated positrons, (iii) inclusion of astrophysical background from gamma-ray sources. The conservative constraint is significantly improved by more than an order of magnitude at $2\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }\text{ }\mathrm{g}\ensuremath{\lesssim}M\ensuremath{\lesssim}{10}^{17}\text{ }\text{ }\mathrm{g}$ over the past relevant work, where the effect (ii) is dominant. After further accounting for the astrophysical background, more than a tenfold improvement extends to a much wider mass range ${10}^{15}\text{ }\text{ }\mathrm{g}\ensuremath{\lesssim}M\ensuremath{\lesssim}2\ifmmode\times\else\texttimes\fi{}{10}^{17}\text{ }\text{ }\mathrm{g}$.