Primordial black holes (PBHs) with masses below 10⁹\, g 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 10⁰-10²\, g for k=2 are unconstrained by observations.
Chaudhuri et al. (Wed,) studied this question.