Existence of primordial black holes across key mass ranges

Establish whether primordial black holes formed in any of the following mass ranges: less than 10^15 g (probing the early Universe via evaporation), greater than 10^15 g (probing gravitational collapse where Hawking evaporation is negligible), approximately 10^15 g (probing high-energy physics through Hawking radiation), and approximately 10^-5 g (probing quantum gravity at the Planck mass scale).

Background

The paper outlines four mass ranges that make the paper of primordial black holes (PBHs) uniquely informative: M < 10^15 g (early Universe), M > 10^15 g (gravitational collapse), M ≈ 10^15 g (high-energy physics), and M ≈ 10^-5 g (quantum gravity). These categories reflect distinct physical regimes and observational consequences, such as Hawking evaporation for the lightest PBHs and dynamical and accretion effects for heavier ones.

Despite the breadth of theoretical motivations and potential observational signatures, the authors explicitly note that it remains uncertain whether PBHs actually formed in any of these ranges. Resolving this would have far-reaching implications for cosmology, particle physics, and quantum gravity.