New bounds on memory burdened primordial black holes from Big Bang nucleosynthesis

Abstract Primordial black holes (PBHs) with masses below 10 9 grams are typically assumed to have negligible cosmological impact due to their rapid evaporation via Hawking radiation. However, the “memory burden” effect, which is a quantum suppression of PBH evaporation, can dramatically alter their decay dynamics. In this work, we revisit early-Universe constraints on ultralight PBHs in this mass range, demonstrating that memory burden significantly alters previous constraints. We compute new cosmological bounds from BBN that strongly limit the presence of ultralight PBHs in the early Universe. We report that the PBHs in the mass range 10 0 –10 2 g for a suppression parameter k = 2, where k quantifies the strength of the memory burden effect, are unconstrained by observations.