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We consider a novel approach to address the black hole information paradox. The idea is based on adapting, to the situation at hand, the modified versions of quantum theory involving spontaneous stochastic dynamical collapse of quantum states, which have been considered in attempts to deal with shortcomings of the standard Copenhagen interpretation of quantum mechanics, in particular, the issue known as "the measurement problem." The new basic hypothesis is that the modified quantum behavior is enhanced in the region of high curvature so that the information encoded in the initial quantum state of the matter fields is rapidly erased as the black hole singularity is approached. We show that in this manner the complete evaporation of the black hole via Hawking radiation can be understood as involving no paradox. Calculations are performed using a modified version of quantum theory known as "continuous spontaneous localization" (CSL), which was originally developed in the context of many-particle nonrelativistic quantum mechanics. We use a version of CSL tailored to quantum field theory and applied in the context of the two -dimensional Callan-Giddings-Harvey-Strominger model. Although the role of quantum gravity in this picture is restricted to the resolution of the singularity, related studies suggest that there might be further connections. [ABSTRACT FROM AUTHOR]

We study gravitational lensing by a recently proposed black hole solution in loop quantum gravity. We highlight the fact that the quantum gravity corrections to the Schwarzschild metric in this model evade the "mass suppression" effects (that the usual quantum gravity corrections are susceptible to) by virtue of one of the parameters in the model being dimensionless, which is unlike any other quantum gravity motivated parameter. Gravitational lensing in the strong and weak deflection regimes is studied, and a sample consistency relation is presented which could serve as a test of this model. We discuss that, though the consistency relation for this model is qualitatively similar to what would have been in Brans-Dicke, in general it can be a good discriminator between many alternative theories. Although the observational prospects do not seem to be very optimistic even for a galactic supermassive black hole case, time delay between relativistic images for a billion solar mass black holes in other galaxies might be within reach of future relativistic lensing observations. [ABSTRACT FROM AUTHOR]

We discuss photon and test-particle orbits in the Kehagias-Sfetsos (KS) metric of Horava's gravity. For any value of the Horava parameter ω, there are values of the gravitational mass M for which the metric describes a naked singularity, and this is always accompanied by a vacuum "antigravity sphere" on whose surface a test particle can remain at rest (in a zero angular momentum geodesic), and inside which no circular geodesies exist. The observational appearance of an accreting KS naked singularity in a binary system would be that of a quasistatic spherical fluid shell surrounded by an accretion disk, whose properties depend on the value of M, but are always very different from accretion disks familiar from the Kerr-metric solutions. The properties of the corresponding circular orbits are qualitatively similar to those of the Reissner-Nordstrom naked singularities. When event horizons are present, the orbits outside the Kehagias-Sfetsos black hole are qualitatively similar to those of the Schwarzschild metric. [ABSTRACT FROM AUTHOR]

The black hole final state proposal reconciles the Mailing vacuum with the unitarity of the Hawking radiation, but only for some experiments. We study experiments that first verify the exterior, then the interior purification of the same Hawking particle. (This is the same protocol that renders the firewall paradox operationally meaningful in standard quantum mechanics.) We show that the decoherence functional fails to be diagonal, even upon inclusion of external''pointer" systems. Hence, probabilitiesforoutcomesofthese measurements are not defined. We conclude that the final state proposal does not offer a consistent alternative to the firewall hypothesis. [ABSTRACT FROM AUTHOR]

We present the detailed analyses of a model of loop quantum Schwarzschild interior coupled to a massless scalar field and extend the results in our previous rapid communication [C. Zhang, Y. Ma, S. Song, and X. Zhang, Loop quantum Schwarzschild interior and black hole remnant, Phys. Rev. D 102, 041502 (2020)] to more general schemes. It is shown that the spectrum of the black hole mass is discrete and does not contain zero. This supports the existence of a black hole remnant after Hawking evaporation due to loop quantum gravity effects. Besides to show the existence of a nonvanishing minimal black hole mass in the vacuum case, the quantum dynamics for the nonvacuum case is also solved and compared with the effective one. [ABSTRACT FROM AUTHOR]

We consider the loop quantum theory of the spherically symmetric model of gravity coupled to Gaussian dust fields, where the Gaussian dust fields provide a material reference frame of the space and time to deparametrize gravity. This theory, used to study the quantum features of the spherically symmetric BH, is constructed based on a 1-dimensional lattice γ⊂R. Taking advantage of the path integral formulation, we investigate the quantum dynamics and obtain an effective action. With this action, we get an effective continuous description of this quantum lattice system which is not the same as the one described by the effective Hamiltonian used in [M. Han and H. Liu, Improved effective dynamics of loop-quantum-gravity black hole and Nariai limit], i.e., the classical Hamiltonian with the holonomy correction. It turns out that, the Hamiltonian derived in this paper can return to that used in [M. Han and H. Liu] only for macro black holes, since the lattice γ is required to be sufficiently fine. Indeed, it is necessary to propose this fine-grained lattice structure in order to well describe the underlying lattice theory by the continuous description. [ABSTRACT FROM AUTHOR]

We undertake the task of studying the nonlinear dynamics of quantum gravity motivated alternatives to black holes that in the classical limit appear as ultracompact shells of matter. We develop a formalism that should be amenable to numerical solution in generic situations. For a concrete model, we focus on the spherically symmetric anti-de Sitter (AdS) black bubble--a shell of matter at the Buchdahl radius separating a Schwarzschild exterior from an AdS interior. We construct a numerical code to study the radial dynamics of and accretion onto AdS black bubbles, with exterior matter provided by scalar fields. In doing so, we develop numerical methods that could be extended to future studies beyond spherical symmetry. Regarding AdS black bubbles in particular, we find that the original prescription for the internal matter fluxes needed to stabilize the black bubble is inadequate in dynamical settings, and we propose a two-parameter generalization of the flux model to fix this. To allow for more efficient surveys of parameter space, we develop a simpler numerical model adapted to spherically symmetric bubble dynamics. We identify regions of parameter space that do allow for stable black bubbles and moreover allow control to a desired end state after an accretion episode. Based on these results, and evolution of scalar fields on black bubble backgrounds, we speculate on some observational consequences if what are currently presumed to be black holes in the Universe were actually black bubbles. [ABSTRACT FROM AUTHOR]

We study some consequences of the loop quantization of the outermost dust shell in the Lemaître-Tolman-Bondi spacetime with a homogeneous dust density using different quantization strategies motivated by loop quantum gravity. Prior work has dealt with loop quantizing this model by employing holonomies and the triads, following the procedure in standard loop quantum cosmology. In this work we compare this quantization with the one in which holonomies and gauge-covariant fluxes are used. While both of the quantization schemes resolve the central singularity, they lead to different mass gaps at which a trapped surface forms. This trapped surface which is matched to an exterior generalized Vaidya spacetime disappears when the density of the dust cloud is in the Planck regime. We find that the quantization based on holonomies and gauge-covariant fluxes generically results in an asymmetric evolution of the dust shell in which the Vaidya mass associated with the white hole as seen by an external observer is 2/π of the one for the black hole. This effective difference in masses results from difference in the classical limits in pre- and postbounce regimes in the two quantizations. This distinctive feature rules out formation of any black-hole-white-hole twins in presence of gauge-covariant flux modifications, which is in contrast to the quantization using holonomies and triads where the gravitational collapse always leads to black hole-white hole twins. Another striking difference lies in the fact that for the quantization based on holonomies and gauge-covariant fluxes there can be situations in which during a nonsingular collapse only a black hole forms without a white hole. [ABSTRACT FROM AUTHOR]

We first show that stationary black holes satisfy an extremely simple quasilocal form of the first law, dE=? /8pdA, where the (quasilocal) energy E=A/(8pl) and (local) surface gravity ? =1/l, with A the horizon area and l is a proper length characterizing the distance to the horizon of a preferred family of quasilocal observers suitable for thermodynamical considerations. Our construction is extended to the more general framework of isolated horizons. The local surface gravity is universal. This has important implications for semiclassical considerations of black hole physics as well as for the fundamental quantum description arising in the context of loop quantum gravity. [ABSTRACT FROM AUTHOR]

Using the SL(2, R) duality in a dimensionally reduced spacetime in (the bosonic sector of) five- dimensional minimal supergravity, we construct general Kaluza-Klein black hole solutions which carry six independent charges: its mass, angular momentum along four dimensions, and electric and magnetic charges of the Maxwell fields, in addition to Kaluza-Klein electric and magnetic monopole charges. [ABSTRACT FROM AUTHOR]

Warp drives are space-times allowing for superluminal travel. However, they are quantum mechanically unstable because they produce a Hawking-like radiation which is blue shifted at their front wall without any bound. We reexamine this instability when local Lorentz invariance is violated at ultrahigh energy by dispersion, as in some theories of quantum gravity. Interestingly, even though the ultraviolet divergence is now regulated, warp drives are still unstable. Moreover the type of instability is different whether one uses a subluminal or a superluminal dispersion relation. In the first case, a black-hole laser yields an exponential amplification of the emitted flux whereas, in the second, infrared effects produce a linear growth of that flux. These results suggest that chronology could still be protected when violating Lorentz invariance. [ABSTRACT FROM AUTHOR]

Attempts to formulate a quantum theory of gravitation are collectively known as quantum gravity. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special relativity theories predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called generalized uncertainty principle (GUP). We have proposed a GUP consistent with string theory, black hole physics, and doubly special relativity theories and have showed that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it suggests that the space that confines it must be quantized, and in fact that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this may signal the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale. Because this influences all the quantum Hamiltonians in an universal way, it predicts quantum gravity corrections to various quantum phenomena. Therefore, in the present work we compute these corrections to the Lamb shift, simple harmonic oscillator, Landau levels, and the tunneling current in a scanning tunneling microscope. [ABSTRACT FROM AUTHOR]

We consider a cosmological model based upon a noncanonical noncommutative extension of the Heisenberg-Weyl algebra to address the thermodynamical stability and the singularity problem of black holes whose interior are described by the Kantowski-Sachs metric and modeled by a noncommutative extension of the Wheeler-DeWitt equation. We compute the temperature and entropy of these black holes and compare the results with the Hawking values. We observe that it is actually the noncommutativity in the momentum sector that allows for the existence of a minimum in the potential, which is the key to apply the Feynman-Hibbs procedure. It is shown that this noncommutative model generates a nonunitary dynamics that predicts a vanishing probability in the neighborhood of the singularity. This result effectively regularizes the Kantowski-Sachs singularity and generalizes a similar result, previously obtained for the case of Schwarzschild black holes. [ABSTRACT FROM AUTHOR]

The dynamics of particle, event, and apparent horizons in Friedmann-Lemaitre-Robertson-Walker space are discussed. The apparent horizon is trapping when the Ricci curvature is positive. This simple criterion coincides with the condition for the Kodama-Hayward apparent horizon temperature to be positive and also discriminates between the timelike and spacelike character of the apparent horizon. We discuss also the entropy of apparent cosmological horizons in extended theories of gravity and we use the generalized 2nd law to discard an exact solution of Brans-Dicke gravity as unphysical. [ABSTRACT FROM AUTHOR]

In the case of a large class of static, spherically symmetric black hole solutions in higher order modified gravity models, an expression for the associated energy is proposed and identified with a quantity proportional to the constant of integration, which appears in the explicit solution. The identification is achieved making use of derivation of the first law of black hole thermodynamics from the equations of motion, evaluating independently the entropy via the Wald method and the Hawking temperature via quantum mechanical methods in curved space-times. Several nontrivial examples are discussed, including a new topological higher derivative black hole solution, and the proposal is shown to work in all examples considered. [ABSTRACT FROM AUTHOR]

We study the thermodynamics and the thermodynamic geometries of charged rotating Bañados-Teitelboim-Zanelli black holes in (2 + 1)-gravity. We investigate the thermodynamics of these systems within the context of the Weinhold and Ruppeiner thermodynamic geometries and the recently developed formalism of geometrothermodynamics. Considering the behavior of the heat capacity and the Hawking temperature, we show that Weinhold and Ruppeiner geometries cannot describe completely the thermo-dynamics of these black holes and of their limiting case of vanishing electric charge. In contrast, the Legendre invariance imposed on the metric in geometrothermodynamics allows one to describe the charged rotating Bañados-Teitelboim-Zanelli black holes and their limiting cases in a consistent and invariant manner. [ABSTRACT FROM AUTHOR]

The quantum origin of cosmological primordial perturbations is a cornerstone framework in the interplay between gravity and quantum physics. In this paper, we study the mutual information between two spatial regions in a radiation-dominated universe filled by a curvature perturbation field in a squeezed state. We find an enhancement with respect to the usual mutual information of the Minkowski vacuum due to momentum modes affected by particle production during inflation. This result supports our previous claim of the existence of long-range correlations between primordial black holes (PBH) at formation during the radiation era. [ABSTRACT FROM AUTHOR]

In this work we define a new type of flux operators on the Hilbert space of loop quantum gravity. We use them to solve an equation of the form F(A)=cΣ in loop quantum gravity. This equation, which relates the curvature of a connection A with its canonical conjugate Σ=*E, plays an important role for spherically symmetric isolated horizons, and, more generally, for maximally symmetric geometries and for the Kodama state. If the equation holds, the new flux operators can be interpreted as a quantization of surface holonomies from higher gauge theory. Also, they represent a kind of quantum deformation of SU(2). We investigate their properties and discuss how they can be used to define states that satisfy the isolated horizon boundary condition in the quantum theory. [ABSTRACT FROM AUTHOR]

We consider black hole interiors of arbitrary genus number within the paradigm of noncommutative geometry. The study is performed in two ways: One way is a simple smearing of a matter distribution within the black hole. The resulting structure is often known in the literature as a "model inspired by noncommutative geometry." The second method involves a more fundamental approach, in which the Hamiltonian formalism is utilized and a nontrivial Poisson bracket is introduced between the configuration degrees of freedom, as well as between the canonical momentum degrees of freedom. This is done in terms of connection variables instead of the more common ADM variables. Connection variables are utilized here since noncommutative effects are usually inspired from the quantum theory, and it is the connection variables that are used in some of the more promising modern theories of quantum gravity. We find that in the first study, the singularity of the black holes can easily be removed. In the second study, we find that introducing a nontrivial bracket between the connections (the configuration variables) may delay the singularity, but not necessarily eliminate it. However, by introducing a nontrivial bracket between the densitized triads (the canonical momentum variables), the singularity can generally be removed. In some cases, new horizons also appear due to the noncommutativity. [ABSTRACT FROM AUTHOR]

We analyze the classical configurations of a bootstrapped Newtonian potential generated by homogeneous spherically symmetric sources in terms of a quantum coherent state. We first compute how the mass and mean wavelength of these solutions scale in terms of the number of quanta in the coherent state. We then note that the classical relation between the ADM mass and the proper mass of the source naturally gives rise to a generalized uncertainty principle (GUP) for the size of the gravitational radius in the quantum theory. Consistency of the mass and wavelength scalings with this GUP requires the compactness remains at most of order one even for black holes, and the corpuscular predictions are thus recovered, with the quantized horizon area expressed in terms of the number of quanta in the coherent state. Our findings could be useful for analyzing the classicalization of gravity in the presence of matter and the avoidance of singularities in the gravitational collapse of compact sources. [ABSTRACT FROM AUTHOR]

Combining insights from both the effective field theory of quantum gravity and black hole thermodynamics, we derive two novel consistency relations to be satisfied by any quantum theory of gravity. First, we show that a particular combination of the number of massless (light) fields in the theory must take integer values. Second, we show that, once the massless spectrum is fixed, the Wilson coefficient of the Kretschmann scalar in the low-energy effective theory is fully determined by the logarithm of a single natural number. [ABSTRACT FROM AUTHOR]

In the loop quantum gravity context, there have been numerous proposals to quantize the reduced phase space of a black hole and develop a classical effective description for its interior which eventually resolves the singularity. However, little progress has been made toward understanding the relation between such quantum/effective minisuperspace models and what would be the spherically symmetric sector of loop quantum gravity. In particular, it is not clear whether one can extract the phenomenological predictions obtained in minisuperspace models, such as the singularity resolution and the spacetime continuation beyond the singularity, based on results in full loop quantum gravity. In this paper, we present an attempt in this direction in the context of Kantowski-Sachs spacetime, through the proposal of two new effective Hamiltonians for the reduced classical model. The first is derived using Thiemann classical identities for the regularized expressions, while the second is obtained as a first approximation of the expectation value of a Hamiltonian operator in loop quantum gravity in a semiclassical state peaked on the Kantowski-Sachs initial data. We then proceed with a detailed analysis of the dynamics they generate and compare them with the Hamiltonian derived in general relativity and the common effective Hamiltonian proposed in earlier literature. [ABSTRACT FROM AUTHOR]

Canonical quantization of general relativity does not yield a unique quantum theory for gravity. This is in part due to operator ordering ambiguities. In this paper, we investigate the role of different operator orderings on the question of whether a big bang or big crunch singularity occurs. We do this in the context of the minisuperspace model of a Friedmann-Lemaître-Robertson-Walker universe with Brown-Kuchař dust. We find that for a certain class of operator orderings such a singularity is eliminated without having to impose boundary conditions. [ABSTRACT FROM AUTHOR]

How can a Schwarzschild-sized matter system avoid a fate of gravitational collapse? To address this question, we critically reexamine the arguments that led to the "Buchdahl bound," which implies that the minimal size of a stable, compact object must be larger than nine eighths of its own Schwarzschild radius. Following Mazur and Mottola, and in line with other counterexamples to the singularity theorems, we identify large negative radial pressure extending to the gravitational radius as the essential ingredient for evading the Buchdahl bound. Our results are novel although consistent with many other investigations of models of nonsingular black holes. It is shown in particular that a large negative pressure in the framework of classical GR translates into a large positive pressure once quantum physics is incorporated. In this way, a Schwarzschild-sized bound state of closed, interacting fundamental strings in its high-temperature Hagedorn phase can appear to have negative pressure and thus the ability to resist gravitational collapse. [ABSTRACT FROM AUTHOR]

In this work we consider a two-dimensional quantum black hole sourced by the trace anomaly of a conformal field theory. By using holography, we are able to prove that the black hole size is always proportional to the number of states inside the black hole, a result that might be interpreted as a two-dimensional version of the Bekenstein entropy law. Finally, we also show that such a black hole has a minimal size (a remnant). Extrapolating this result for higher dimensions, we show that this would imply that the remnant has a size way larger than the Planck length and is, therefore, always weakly coupled. [ABSTRACT FROM AUTHOR]