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Local Approach to Hawking Radiation

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 Added by Ari Peltola
 Publication date 2008
  fields Physics
and research's language is English
 Authors Ari Peltola




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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.



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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.
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.
We study various derivations of Hawking radiation in conformally rescaled metrics. We focus on two important properties, the location of the horizon under a conformal transformation and its associated temperature. We find that the production of Hawking radiation cannot be associated in all cases to the trapping horizon because its location is not invariant under a conformal transformation. We also find evidence that the temperature of the Hawking radiation should transform simply under a conformal transformation, being invariant for asymptotic observers in the limit that the conformal transformation factor is unity at their location.
The theory of Hawking radiation can be tested in laboratory analogues of black holes. We use light pulses in nonlinear fiber optics to establish artificial event horizons. Each pulse generates a moving perturbation of the refractive index via the Kerr effect. Probe light perceives this as an event horizon when its group velocity, slowed down by the perturbation, matches the speed of the pulse. We have observed in our experiment that the probe stimulates Hawking radiation, which occurs in a regime of extreme nonlinear fiber optics where positive and negative frequencies mix.
We investigate wave optical imaging of black holes with Hawking radiation. The spatial correlation function of Hawking radiation is expressed in terms of transmission and reflection coefficients for scalar wave modes and evaluated by taking summation over angular qunatum numbers numerically for the Unruh-Hawking state of the Kerr-de Sitter black hole. Then wave optical images of evaporating black hole are obtained by Fourier transformation of the spatial correlation function. For short wavelength, the image of the black hole with the outgoing mode of the Unruh-Hawking state looks like a star with its surface is given by the photon sphere. It is found that interference between incoming modes from the cosmological horizon and reflected modes due to scattering of the black hole can enhance brightness of images in the vicinity of the photon sphere. For long wavelenth, whole field of view becomes bright and emission region of Hawking radiation cannot be identifed.
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