Primordial black holes in loop quantum cosmology: the effect on the threshold

Abstract

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 $\delta_\mathrm{c}$, which in general depends on the underlying gravity theory. Up to now, the majority of analytic and numerical techniques calculate $\delta_\mathrm{c}$ 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 cosmology (LQC). In particular, for low mass PBHs formed close to the quantum bounce, we find a reduction in the value of $\delta_\mathrm{c}$ 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 $\gamma$ of loop quantum gravity (LQG) we show its effect on the value of $\delta_\mathrm{c}$ 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.

Remnant loop quantum black holes

“…The modeling of dark matter as relic Planckian black holes is as old as the discussion about their stability [1,[34][35][36][37][38]. The formation of Planck mass black holes at the end of the inflationary phase has been recently investigated as resulting from the collisions of high energy particles [35,36].…”

Shadows of loop quantum black holes: semi-analytical simulations of loop quantum gravity effects on Sagittarius A* and M87*

“…A key question has emerged regarding whether LQG effects in the loop quantum spacetime can produce any observational signatures for current and future experiments, allowing us to test the effect of LQG. This has spurred a surge of studies over the past decades, drawing from various experiments and observations [e.g., 12,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. In [36], LQG effects on the shadow of the rotating black hole are discussed in detail.…”

Primordial Black hole formation from overlapping cosmological fluctuations

“…See also[34,35] based on[33] for a scenario with a time-dependent equation of state and in loop quantum cosmology respectively.2 It should be noted that, in our setting, the fluctuations in two different scales are always overlapping.However, the corresponding features in the compaction function do not necessarily significantly overlap with each other. Readers should clearly distinguish the overlapping of the fluctuations from the overlapping in the profile of the compaction function.…”