Primordial black holes in loop quantum gravity: The effect on the threshold

. Primordial black holes form in the early Universe and constitute one of the most viable candidates for dark matter. The study of their formation process requires the determination of a critical energy density perturbation threshold δ c , which in general depends on the underlying gravity theory. Up to now, the majority of analytic and numerical techniques calculate δ c within the framework of general relativity. In this work, using simple physical arguments we estimate semi-analytically the PBH formation threshold within the framework of quantum gravity, working for concreteness within loop quantum gravity (LQG), which constitutes a non-perturbative and background-independent quantization of general relativity. In particular, for low mass PBHs formed close to the quantum bounce, we find a reduction in the value of δ c up to 50% compared to the general relativistic regime quantifying for the first time to the best of our knowledge how quantum effects can influence PBH formation within a quantum gravity framework. Finally, by varying the Barbero-Immirzi parameter γ of LQG we show its effect on the value of δ c while using the observational/phenomenological signatures associated to ultra-light PBHs, namely the ones affected by LQG effects, we propose the PBH portal as a novel probe to constrain the potential quantum nature of gravity.