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Vacuum spherically symmetric loop quantum gravity in the midi-superspace approximation using inhomogeneous horizon-penetrating slices has been studied for a decade, and it has been noted that the singularity is eliminated. It is replaced by a region of high curvature and potentially large quantum fluctuations. It was recently pointed out that the effective semiclassical metric implies the existence of a shell of matter which violates energy conditions in regions where the curvature is largest. Here, we propose an alternative way of treating the problem that is free from the shells. The ambiguity in the treatment is related with the existence of new observables in the quantum theory that characterize the area excitations, and how the counterpart of diffeomorphisms in the discrete quantum theory is mapped to the continuum semiclassical picture. The resulting spacetime in the high curvature region inside the horizon is approximated by a metric of the type of the Simpson–Visser wormhole and it connects the black hole interior to a white hole in a smooth manner. [ABSTRACT FROM AUTHOR]

In recent decades, there has been growing interest in the quantization of black holes using techniques developed in loop quantum cosmology. Due to the quantum geometry effect, the resulting quantum-corrected black hole provides non-singular models. The quantization scheme can be roughly divided into four types: (1) the μ 0 scheme, (2) the μ ¯ scheme, (3) the generalized μ 0 scheme, and (4) the quantum collapsing model. This paper provides an introduction of the loop quantum black hole model, a summary of the progress made in this field, as well as the quantum effective dynamics and physical applications of these models. [ABSTRACT FROM AUTHOR]

Recently, thermodynamics has given an important aspect of black hole physics, and it is being used as a solemn tool in characterizing the physicality and viability of many black hole (BH) solutions. On the other hand, Heisenberg algebraic deformations, which predict a lower bound to position and/or momentum, are interrogated to have a theory of quantum gravity. In this paper, we consider a combined deformation of the generalized uncertainty and extended generalized uncertainty principles (EGUP) and investigate the EGUP-corrected thermal quantities of the rotating charged BTZ BH. [ABSTRACT FROM AUTHOR]

This work investigates the combined dynamics of the Yang–Mills and Liouville gravity fields at the event horizon of black holes. To analyze quantum dynamics at the event horizon of black holes existing in a three-dimensional (spatial) universe, a two-dimensional formulation is introduced. The following hypothesis is proposed in this work: there exists a two-dimensional analogue to the Higgs field at the event horizon. This field is then considered as a two-dimensional Yang–Mills field. The interaction and symmetry breaking of the combined two-dimensional Yang–Mills and Liouville gravitational fields are then discussed. The resulting gravitational scalar boson and its implications to the quantum dynamics occurring at the event horizon are presented. [ABSTRACT FROM AUTHOR]

In this paper, we construct a solvable toy model of the quantum dynamics of the interior of a spherical black hole with falling spherical scalar field excitations. We first argue about how some aspects of the quantum gravity dynamics of realistic black holes emitting Hawking radiation can be modeled using Kantowski–Sachs solutions with a massless scalar field when one focuses on the deep interior region r ≪ M (including the singularity). Further, we show that in the r ≪ M regime, and in suitable variables, the KS model becomes exactly solvable at both the classical and quantum levels. The quantum dynamics inspired by loop quantum gravity is revisited. We propose a natural polymer quantization where the area a of the orbits of the rotation group is quantized. The polymer (or loop) dynamics is closely related to the Schroedinger dynamics away from the singularity with a form of continuum limit naturally emerging from the polymer treatment. The Dirac observable associated with the mass is quantized and shown to have an infinite degeneracy associated with the so-called ϵ -sectors. Suitable continuum superpositions of these are well-defined distributions in the fundamental Hilbert space and satisfy the continuum Schroedinger dynamics. [ABSTRACT FROM AUTHOR]

Astrophysical objects and the surrounding geometry must be described by suitable states in the complete quantum theory of matter and gravity. We attempt at reconstructing such a state for a Schwarzschild black hole from the analysis of a collapsing ball of dust and describing the outer geometry by means of a coherent state. [ABSTRACT FROM AUTHOR]

One of the foremost goals of theoretical modern physics is to obtain a reliable theory of quantum gravity. In so doing, new fundamental scales are being proposed. For example, in the Snyder–de Sitter (SdS) model, two scales manifest which relate measurement limits of the position and momentum. In this work, we study the thermodynamic functions of the Schwarzschild black hole in the SdS model within the presence of position independent and dependent gravity's rainbow. Heuristically, we prove the presence of a nonzero lower bound value of the horizon, mass and temperature of the black hole. Then, we present the stability and remnant conditions of the black hole according to the entropy and heat capacity functions. [ABSTRACT FROM AUTHOR]

In this paper, we consider the theory of infinitely extended particles as the quantum theory of gravity, which unifies all fundamental interactions. We write the space–time metric, which is Schwarzschild-like black hole. We calculate Hamiltonian and Lagrangian, and from these, we obtain the potential energy and study the polymer quantization. We construct effective potential and discuss the gravitational wave of this theory. Also, we study the geodesic motion of a particle near the black hole. Finally, we analyze the apparent shape, radius and distortion of the shadow of the black hole. [ABSTRACT FROM AUTHOR]

We study a precise and computationally tractable notion of operator complexity in holographic quantum theories, including the ensemble dual of Jackiw-Teitelboim gravity and two-dimensional holographic conformal field theories. This is a refined, "microcanonical" version of K-complexity that applies to theories with infinite or continuous spectra (including quantum field theories), and in the holographic theories we study exhibits exponential growth for a scrambling time, followed by linear growth until saturation at a time exponential in the entropy — a behavior that is characteristic of chaos. We show that the linear growth regime implies a universal random matrix description of the operator dynamics after scrambling. Our main tool for establishing this connection is a "complexity renormalization group" framework we develop that allows us to study the effective operator dynamics for different timescales by "integrating out" large K-complexities. In the dual gravity setting, we comment on the empirical match between our version of K-complexity and the maximal volume proposal, and speculate on a connection between the universal random matrix theory dynamics of operator growth after scrambling and the spatial translation symmetry of smooth black hole interiors. [ABSTRACT FROM AUTHOR]

Classical black holes shield us from the singularities that inevitably appear in general relativity. Singularity regularization being one of the main landmarks for a successful theory of quantum gravity, quantum black holes are not obliged to hide their inner core from the outside world. Notwithstanding the aforesaid, it is often implicitly assumed that quantum gravity effects must remain confined to black hole interiors. In this essay, we argue in the opposite direction, discussing theoretical evidence for the existence of strong correlations between the physics inside and outside nonsingular black holes. We conclude that astronomical tests of the surroundings of black holes can provide invaluable information about their so-far unexplored interiors. [ABSTRACT FROM AUTHOR]

After considering the quantum corrections of Einstein-Maxwell theory, the effective theory will contain some higher-curvature terms and nonminimally coupled electromagnetic fields. In this paper, we study the first law of black holes in the gravitational electromagnetic system with the Lagrangian ℒ(gab, Rabcd, Fab). Firstly, we calculate the Noether charge and the variational identity in this theory, and then generically derive the first law of thermodynamics for an asymptotically flat stationary-axisymmetric symmetric black hole without the requirement that the electromagnetic field is smooth on the bifurcation surface. Our results indicate that the first law of black hole thermodynamics might be valid for the Einstein-Maxwell theory with some quantum corrections in the effective region. [ABSTRACT FROM AUTHOR]

We study the 'improved dynamics' for the treatment of spherically symmetric space-times in loop quantum gravity introduced by Chiou et al in analogy with the one that has been constructed by Ashtekar, Pawlowski and Singh for the homogeneous space-times. In this dynamics the polymerization parameter is a well motivated function of the dynamical variables, reflecting the fact that the quantum of area depends on them. Contrary to the homogeneous case, its implementation does not trigger undesirable physical properties. We identify semiclassical physical states in the quantum theory and derive the corresponding effective semiclassical metrics. We then discuss some of their properties. Concretely, the space-time approaches sufficiently fast the Schwarzschild geometry at low curvatures. Besides, regions where the singularity is in the classical theory get replaced by a regular but discrete effective geometry with finite and Planck order curvature, regardless of the mass of the black hole. This circumvents trans-Planckian curvatures that appeared for astrophysical black holes in the quantization scheme without the improvement. It makes the resolution of the singularity more in line with the one observed in models that use the isometry of the interior of a Schwarzschild black hole with the Kantowski–Sachs loop quantum cosmologies. One can observe the emergence of effective violations of the null energy condition in the interior of the black hole as part of the mechanism of the elimination of the singularity. [ABSTRACT FROM AUTHOR]

We present a geometric classification of all spherically symmetric spacetimes that could result from singularity regularization, using a kinematic construction that is both exhaustive and oblivious to the dynamics of the fields involved. Due to the minimal geometric assumptions underlying it, this classification encompasses virtually all modified gravity theories, and any theory of quantum gravity in which an effective description in terms of an effective metric is available. The first noteworthy conclusion of our analysis is that the number of independent classes of geometries that can be constructed is remarkably limited, with no more than a handful of qualitatively different possibilities. But our most remarkable result is that this catalogue of possibilities clearly demonstrates that the degree of internal consistency and the strength of deviations with respect to general relativity are strongly, and positively, correlated. Hence, either quantum fluctuations of spacetime come to the rescue and solve these internal consistency issues, or singularity regularization will percolate to macroscopic (near-horizon) scales, radically changing our understanding of black holes and opening new opportunities to test quantum gravity. [ABSTRACT FROM AUTHOR]

We point out that two-dimensional Russo-Susskind-Thorlacius (RST) model for evaporating black holes is locally equivalent — at the full quantum level — to flat-space Jackiw-Teitelboim (JT) gravity that was recently shown to be unitary. Globally, the two models differ by a reflective spacetime boundary added in the RST model. Treating the boundary as a local and covariant deformation of quantum JT theory, we develop sensible semiclassical description of evaporating RST black holes. Nevertheless, our semiclassical solutions fail to resolve the information recovery problem, and they do not indicate formation of remnants. This means that either the standard semiclassical method incorrectly describes the evaporation process or the RST boundary makes the flat-space JT model fundamentally inconsistent. [ABSTRACT FROM AUTHOR]

We study equilibrium configurations of a homogenous ball of matter in a bootstrapped description of gravity which includes a gravitational self-interaction term beyond the Newtonian coupling. Both matter density and pressure are accounted for as sources of the gravitational potential for test particles. Unlike the general relativistic case, no Buchdahl limit is found and the pressure can in principle support a star of arbitrarily large compactness. By defining the horizon as the location where the escape velocity of test particles equals the speed of light, like in Newtonian gravity, we find a minimum value of the compactness for which this occurs. The solutions for the gravitational potential here found could effectively describe the interior of macroscopic black holes in the quantum theory, as well as predict consequent deviations from general relativity in the strong field regime of very compact objects. [ABSTRACT FROM AUTHOR]

The motivation behind this study is to enumerate the leading order corrections to the thermodynamics of BTZ black hole (named after three scientists; Banados, Teitelboim, and Zanelli). We first analyze the effect of quantum corrections (motivated from string theory and loop quantum gravity) on various thermodynamic variables for uncharged and stationary BTZ black hole. We, later on, endow charges and rotations to the same black hole and rederive all the expressions once again. The comparative analysis is done between the corrected and uncorrected thermodynamics via plots. [ABSTRACT FROM AUTHOR]

In the standard formalism of quantum gravity, black holes appear to form statistical distributions of quantum states. Now, however, we can present a theory that yields pure quantum states. It shows how particles entering a black hole can generate firewalls, which however can be removed, replacing them by the ‘footprints’ they produce in the out-going particles. This procedure can preserve the quantum information stored inside and around the black hole. We then focus on a subtle but unavoidable modification of the topology of the Schwarzschild metric: antipodal identification of points on the horizon. If it is true that vacuum fluctuations include virtual black holes, then the structure of space-time is radically different from what is usually thought. [ABSTRACT FROM AUTHOR]

We argue that, when certain higher-curvature corrections are added to the four-dimensional Einstein-Hilbert action, black holes become stable below certain mass. We show this to be the case for an infinite family of ghost-free theories involving terms of arbitrarily high order in curvature. The thermodynamic behavior of the new black holes is universal for arbitrary values of the couplings, with the only exception of the Schwarzschild solution itself, which is recovered when all the couplings are set to zero. For this class of theories, the issue of non-unitary evolution is inexistent, as black holes never evaporate completely. [ABSTRACT FROM AUTHOR]

The propagation of light through the metamaterial analogue to the Noncommutative Schwarzschild spacetime is studied. NonCommutative (NC) spacetime properties have been considered in several high energy theories which in the context of gravitation, those may be considered as effective theories of quantum gravity. Following the approach established in [6] , we found the properties related to the metamaterial corresponding to the NC-Schwarzschild spacetime. The main effects observed in the simulations are a deviation in the light path and a difference in the electric field norm of the beam compared to the propagation in the standard Schwarzschild metamaterial. These measurable effects are useful to determine the existence of noncommutativity. Also, metamaterial simulations offer a novel way to explore possible observable consequences of modified theories of General Relativity. • The metamaterial analogue to the noncommutative Schwarzschild black hole is studied. • Ray paths are compared with the full wave simulations showing consistent results. • Differences between the norm of electric fields are proposed in order to measure noncommutative effects. • Metamaterial simulations show to be a novel way to observe consequences of modified theories of General Relativity. [ABSTRACT FROM AUTHOR]

The Nobel Prize in Physics 2021 was awarded for groundbreaking contributions to the understanding of complex systems, jointly to Syukuro Manabe and Klaus Hasselmamm for the physical modelling of the earth's climate and to Giorgio Parisi for his work on the interplay of disorder and fluctuations in physical systems. In fact, complexity and also chaos play an important role in many physical systems, like e.g. in the formations of stars and galaxies.We expect that complexity and chaos will also gain more and more importance for the understanding of quantum gravity, the quantum physics of black holes, holography and also in quantum information theory. Therefore we invite authors to also submit articles with emphasis on these exciting topics to "Fortschritte der Physik". I wish all authors and readers of "Fortschritte der Physik" a happy, healthy and successful new year 2022. Dieter Lüst (Editor) [ABSTRACT FROM AUTHOR]

We consider a microscopic model of a stretched horizon of the Schwarzschild black hole. In our model the stretched horizon consists of a finite number of discrete constituents. Assuming that the quantum states of the Schwarzschild black hole are encoded in the quantum states of the constituents of its stretched horizon in a certain manner we obtain an explicit, analytic expression for the partition function of the hole. Our partition function predicts, among other things, the Hawking effect, and provides it with a microscopic, statistical interpretation. [ABSTRACT FROM AUTHOR]

Using the Boltzmann-Gibbs statistical mechanics together with the quasinormal modes of the black holes and the Bekenstein-Hawking area entropy law, we can determine univocally the lowest possible value for the spin j , which is j m i n = 1 , in the framework of the Loop Quantum Gravity theory. Subsequently, the value of Immirzi parameter is given by γ = ln ⁡ 3 / (2 π 2). In this paper, we have demonstrated that if we use the Barrow formulation for the black hole entropy then the minimum value of the label j depends on the value, which characterizes the fractal structure of the black hole surface called Δ parameter, and may have values other than j m i n = 1. [ABSTRACT FROM AUTHOR]

Using the quasilocal properties alone we show that the area spectrum of a black hole horizon must be discrete, independent of any specific quantum theory of gravity. The area spectrum is found to be half-integer spaced with values 8πγℓ²pj where j∈N/2. We argue that if microstate counting is carried out for quantum states residing on the horizon only, correction of exp(-A/4ℓ²p) over the Bekenstein-Hawking area law must arise in black hole entropy. [ABSTRACT FROM AUTHOR]