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Register a new userThe self-screening Hawking atmosphere
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G. t Hooft
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A model is proposed in which the Hawking particles emitted by a black hole are treated as an envelope of matter that obeys an equation of state, and acts as a source in Einsteins equations. This is a crude but interesting way to accommodate for the back reaction. For large black holes, the solution can be given analytically, if the equation of state is $p=kapparho$, with $0<kappa<1$. The solution exhibits a singularity at the origin. If we assume $N$ free particle types, we can use a Hartree-Fock procedure to compute the contribution of one such field to the entropy, and the result scales as expected as $1/N$. A slight mismatch is found that could be attributed to quantum corrections to Einsteins equations, but can also be made to disappear when $k$ is set equal to one. The case $kappa=1$ is further analysed.
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We have previously presented a reconstruction of Horndeski scalar-tensor theories from linear cosmological observables. It includes free nonlinear terms which can be added onto the reconstructed covariant theory without affecting the background and linear dynamics. After discussing the uniqueness of these correction terms, we apply this nonlinear freedom to a range of different applications. First we demonstrate how the correction terms can be configured to endow the reconstructed models with screening mechanisms such as the chameleon, k-mouflage and Vainshtein effects. A further implication is the existence of classes of Horndeski models that are degenerate with standard cosmology to an arbitrary level in the cosmological perturbations. Particularly interesting examples are kinetically self-accelerating models that mimic the dynamics of the cosmological constant to an arbitrary degree in perturbations. Finally, we develop the reconstruction method further to the level of higher-order effective field theory, which under the restriction to a luminal propagation speed of gravitational waves introduces two new free functions per order. These functions determine the corresponding correction terms in the linearly reconstructed action at the same order. Our results enable the connection of linear cosmological constraints on generalised modifications of gravity and dark energy with the nonlinear regime and astrophysical probes for a more global interpretation of the wealth of forthcoming cosmological survey data.
We derive the Hawking radiation spectrum of anyons, namely particles in (2+1)-dimension obeying fractional statistics, from a BTZ black hole, in the tunneling formalism. We examine ways of measuring the spectrum in experimentally realizable systems in the laboratory.
We consider an approach to the Hawking effect which is free of the asymptotic behavior of the metric or matter fields, and which is not confined to one specific metric configuration. As a result, we find that for a wide class of spacetime horizons there exists an emission of particles out of the horizon. As expected, the energy distribution of the radiating particles turns out to be thermal.
The Hartle-Hawking wave function is known to be the Fourier dual of the Chern-Simons or Kodama state reduced to mini-superspace, using an integration contour covering the whole real line. But since the Chern-Simons state is a general solution of the Hamiltonian constraint (with a given ordering), its Fourier dual should provide the general solution (i.e. beyond mini-superspace) of the Wheeler DeWitt equation representing the Hamiltonian constraint in the metric representation. We write down a formal expression for such a wave function, to be seen as the generalization beyond mini-superspace of the Hartle-Hawking wave function. Its explicit evaluation (or simplification) depends only on the symmetries of the problem, and we illustrate the procedure with anisotropic Bianchi models and with the Kantowski-Sachs model. A significant difference of this approach is that we may leave the torsion inside the wave functions when we set up the ansatz for the connection, rather than setting it to zero before quantization. This allows for quantum fluctuations in the torsion, with far reaching consequences.
In 1974 Steven Hawking showed that black holes emit thermal radiation, which eventually causes them to evaporate. The problem of the fate of information in this process is known as the black hole information paradox. It inspired a plethora of theoretical models which, for the most part, assume either a fundamental loss of information or some form of quantum gravity. At variance to the main trends, a conservative approach assuming information retrieval in quantum correlation between Hawking particles was proposed and recently developed within qubit toy-models. Here we leverage modern quantum information to incarnate this idea in a realistic model of quantised radiation. To this end we employ the formalism of quantum Gaussian states together with the continuous-variables version of the quantum marginal problem. Using a rigorous solution to the latter we show that the thermality of all Hawking particles is consistent with a global pure state of the radiation. Surprisingly, we find out that the radiation of an astrophysical black hole can be thermal until the very last particle. In contrast, the thermality of Hawking radiation originating from a microscopic black hole -- which is expected to evaporate through several quanta -- is not excluded, though there are constraints on modes frequencies. Our result support the conservative resolution to the black hole information paradox. Furthermore, it suggests a systematic programme for probing the global state of Hawking radiation.
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