Probing Loop Quantum Gravity with Evaporating Black Holes

Abstract

This letter aims at showing that the observation of evaporating black holes should allow the usual Hawking behavior to be distinguished from Loop Quantum Gravity (LQG) expectations. We present a full Monte Carlo simulation of the evaporation in LQG and statistical tests that discriminate between competing models. We conclude that contrarily to what was commonly thought, the discreteness of the area in LQG leads to characteristic features that qualify evaporating black holes as objects that could reveal quantum gravity footprints. Introduction-Loop Quantum Gravity (LQG) is a promising framework to nonperturbatively quantize General Relativity (GR) in a background invariant way (see [1] for introductory reviews). Interestingly, it has now been demonstrated that different approaches, based either on quantizations (covariant or canonical) of GR, or on a formal quantization of geometry lead to the very same LQG theory. As for any tentative theory of quantum gravity, experimental tests are however still missing. Trying to find possible observational signatures is obviously a key challenge. In this article we address the following question : could there be objects in the contemporary universe whose observation would lead to a clear signature of LQG ? Fortunately, the answer turns out to be positive. Although small black holes have not yet been directly observed, they could have been formed by different mechanisms in the early universe (see, e.g., [2] for a recent review) or even by particle collisions. We don't review here the well-known possible production mechanisms, but instead we focus on how to use the evaporation of microscopic black holes to investigate the discriminating power of the emitted spectrum. Three different possible signatures will be suggested. Although one should be careful when pushing the limits of the LQG approach to black holes to the microscopic limit, our results rely on features of the area spectrum and are rather insensitive

Semiclassical analysis of black holes in loop quantum gravity: Modeling Hawking radiation with volume fluctuations

“…Note that the black hole spectrum in the deep quantum regime (when n is small) has been studied numerically in [49,50] for instance.…”

Black hole spectroscopy from loop quantum gravity models

“…More precisely, we describe the black hole radiation process using statistical mechanical techniques together with some assumptions about the dynamical behavior of BHs close to equilibrium. In doing this we will basically follow the ideas of [27] leading to the computation of the integrated emission spectrum for a black hole (under some assumptions which will be made precise later). The simulated spectrography will allow for the study of deviations predicted by the old and new (holographic) models of LQG from the semiclassical Hawk-ing process expectation.…”

Loop Quantum Gravity and Observations

“…The idea proposed in [39] is to search for possible LQG signatures in the spectrum of evaporating black holes. The state counting for black holes in LQG relies on the isolated horizon framework (that is a boundary of the underlying manifold considered before quantization).…”

“…However it was understood in [41,42] that the situation is different in LQG because the spacing of the energy levels decreases exponentially with the energy. In [39], this issue was readdressed and it was shown that several different signatures can in fact be expected.…”