Constraints on evaporating primordial black holes from the AMS-02 positron data

Abstract

Cosmic-ray (CR) positrons are relatively rare due to their secondary origin and thus sensitive to exotic contributions. Primordial black holes (PBHs) with masses above $\sim 5\times10^{14}\,\mathrm{g}$ can be stable sources of CR positrons due to Hawking radiation. The energies of the evaporated positrons can increase significantly through scattering with the Galactic random magnetic fields during the propagation in the Galaxy, which is a generic feature in diffusive re-acceleration CR propagation models. We show that in well-constrained diffusive re-acceleration models, a significant portion of CR positron flux can enter the energy region of $\mathcal{O}(\text{GeV})$, and can be constrained by the current AMS-02 data. As an example, we show that in the Galprop+Helmod model for CR propagation in the Galaxy and heliosphere, an upper limit of $f_{\text{PBH}}\lesssim2.15\times 10^{-4}$ at PBH mass $2\times 10^{16}$~g can be obtained, which improve the previous constraints from the Voyager CR all-electron data by around an order of magnitude.