1,721,175 research outputs found
Localised particles and fuzzy horizons: a tool for probing quantum black holes
Full text linkThe horizon is a classical concept that arises in general relativity and is therefore not clearly defined when the source cannot be reliably described by classical physics. To any (sufficiently) localised quantum mechanical wavefunction, one can associate a horizon wavefunction which yields the probability of finding a horizon of given radius centred around the source. We can then associate to each quantum particle a probability that it is a black hole, and the existence of a minimum black hole mass follows naturally, which agrees with the one obtained from the hoop conjecture and the Heisenberg uncertainty principle
QUANTUM FIELDS IN GRAVITY, COSMOLOGY AND BLACK HOLES
No full textThe research area of this project regards the fundamental gravitational interaction and the theoretical study of cosmology and black holes. In our framework, both quantum field theory (QFT) and gravity play essential roles.
In the lack of a fully quantum theory of all interactions including gravity, QFT on curved space-time - where quantum fields describing matter and radiation interact with the non-quantised gravitational field - has historically proved to be a very successful approach. It has produced some of the most significant theoretical predictions of the last 40 years, such as black hole evaporation and the inflationary paradigm. The latter is now supported by observational data and plays the role of the standard model of cosmology.
Moreover, there is increasing evidence that theoretical descriptions of (quantum) gravity may be consistently formulated by employing advanced QFT methods, such as those relying on generalised uncertainty principles, effective actions and the renormalisation group. The paradigms of asymptotic safety, classicalization and possible UV-completeness, or non-perturbative renormalizability, suggest that nowadays, a QFT formulation of gravity may therefore become predictive.
The above scenarios have gained considerable attention and provide alternative routes to a fully consistent formulation of quantum gravity. We wish to employ these ideas to tackle the long-standing problems of the fate of classical singularities, as well as the physics of quantum matter in the presence of (dynamical) horizons, in cosmology and black holes, also including modified gravity theories
Geometry and thermodynamics of coherent quantum black holes
Full text linkIn this paper, we present a quantum description of black holes given by coherent states of gravitons sourced by a matter core. The expected behavior in the weak-field region outside the horizon is recovered, with arbitrarily good approximation, but the classical central singularity is not resolved because the coherent states may not contain modes of arbitrarily short wavelength and the matter core must therefore have finite size. Ensuing quantum corrections both in the interior and exterior is also estimated by assuming that the mean-field approximation holds everywhere. These deviations from the classical black hole geometry can be viewed as quantum hair and will lead to a quantum corrected horizon radius and thermodynamics
The scale(s) of quantum gravity and integrable black holes
No full textIt is often argued that the Planck length (or mass) is the scale of quantum gravity, as shown by comparing the Compton length with the gravitational radius of a particle. However, the Compton length is relevant in scattering processes but does not play a significant role in bound states. We will derive a possible ground state for a dust ball composed of a large number of quantum particles entailing a core with the size of a fraction of the horizon radius. This suggests that quantum gravity becomes physically relevant for systems with compactness of order one for which the nonlinearity of General Relativity cannot be discarded. A quantum corrected geometry can then be obtained from the effective energy-momentum tensor of the core or from quantum coherent states for the effective gravitational degrees of freedom. These descriptions replace the classical singularity of black holes with integrable structures in which tidal forces remain finite and there is no inner Cauchy horizon. The extension to rotating systems is briefly mentioned
Quantum dust cores of black holes
Full text linkWe describe the ground state for a gravitationally collapsed ball of dust as
the direct product of wavefunctions for dust particles distributed over an
arbitrary number of nested layers. This allows us to estimate the expectation
value of the global radius as well as the effective energy density and
pressures for the dust core of quantum black holes. In particular, the size of
the quantum core does not depend on the number of layers and the mass function
is shown to grow linearly with the areal radius up to the outermost layer.Comment: 9 pages, 2 figures. Version to appear in PL
A quantum bound on the compactness
Full text linkWe present a simple quantum description of the gravitational collapse of a ball of dust which excludes those states whose width is arbitrarily smaller than the gravitational radius of the matter source and supports the conclusion that black holes are macroscopic extended objects. We also com- ment briefly on the relevance of this result for the ultraviolet self-completion of gravity and the connection with the cor- puscular picture of black holes
Uncertainty relations and precession of perihelion
No full textWe compute the corrections to the Schwarzschild metric necessary to reproduce the Hawking temperature derived from a Generalized Uncertainty Principle (GUP), so that the GUP deformation parameter is directly linked to the deformation of the metric. Using this modified Schwarzschild metric, we compute corrections to the standard General Relativistic predictions for the perihelion precession for planets in the solar system, and for binary pulsars. This analysis allows us to set bounds for the GUP deformation parameter from well-known astronomical measurements
Singularity avoidance in quantum gravity
Full text linkThe purpose of this work is to investigate the consequences of quantum gravity for the singularity problem. We study the higher-derivative terms that invariably appear in any quantum field theoretical model of gravity, handling them both non-perturbatively and perturbatively. In the former case, by computing the contributions of the additional degrees of freedom to a congruence of geodesics, we show that the appearance of singularities is no longer a necessity. In the latter, which corresponds to treating the quantised general relativity as an effective field theory, we generalise the Hawking-Penrose theorems to include one-loop corrections of both massless matter and graviton fluctuations
The role of collapsed matter in the decay of black holes
Full text linkWe try to shed some light on the role of matter in the final stages of black hole evaporation from the fundamental frameworks of classicalization and the black-to-white hole bouncing scenario. Despite being based on very different grounds, these two approaches attempt at going beyond the background field method and treat black holes as fully quantum systems rather than considering quantum field theory on the corresponding classical manifolds. They also lead to the common prediction that the semiclassical description of black hole evaporation should break down and the system be disrupted by internal quantum pressure, but they both arrive at this conclusion neglecting the matter that formed the black hole. We instead estimate this pressure from the bootstrapped description of black holes, which allows us to express the total Arnowitt–Deser–Misner mass in terms of the baryonic mass still present inside the black hole. We conclude that, although these two scenarios provide qualitatively similar predictions for the final stages, the corpuscular model does not seem to suggest any sizeable deviation from the semiclassical time scale at which the disruption should occur, unlike the black-to- white hole bouncing scenario. This, in turn, makes the phenomenology of corpuscular black holes more subtle from an astrophysical perspective
Star equilibrium: from BNG to TOV
Full text linkWe study the role of the equilibrium equation in
bootstrapped Newtonian gravity (BNG) by including terms
inspired by the post-Newtonian expansion of the Tolman–
Oppenheimer–Volkov (TOV) equation. We then compare
(approximate) BNG solutions for homogenous stars with
their Newtonian and General Relativistic exact solutions.
Regardless of the additional terms from the conservation
equation, BNG stars do not exhibit a Buchdahl limit. How-
ever, specific extra terms added to this equation can cause the
pressure to become negative inside stars with compactness
smaller than the critical values for BNG black hole formation
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