Revisiting the gamma-ray signal from light ALPs emitted during the evaporation of memory-burdened PBHs

Abstract

The memory-burden effect was recently proposed to take into account the information back-reaction in the evaporation of primordial black holes (PBHs). In this work, we systematically explore the axion-like particle (ALP) production via the evaporation of memory-burdened PBHs and the subsequent ALP-photon conversion in cosmic magnetic fields. The PBH evaporation progress is divided in the semiclassical phase of Hawking radiation and the quantum memory-burden phase. The time evolution of PBH mass and the gamma-ray flux after the conversion of PBH-emitted ALP are then evaluated by considering the memory-burden induced PBH entropy suppression. Furthermore, we investigate the detection prospects of this evaporation-conversion signal in next-generation satellite telescopes, including AMEGO, e-ASTROGAM and MAST. The detectable PBH mass range is extended down to masses much smaller than $10^{15}$ g. Applying the Fisher forecasting method, we derive the projected sensitivity for PBH fraction $f_{\rm PBH}$ and ALP-photon coupling $g_{aγγ}$.