1,721,022 research outputs found
Experimental quantum cosmology in time-dependent optical media
Full text linkIt is possible to construct artificial spacetime geometries for light by using intense laser pulses that modify the spatiotemporal properties of an optical medium. Here we theoretically investigate experimental possibilities for studying spacetime metrics of the form . By tailoring the laser pulse shape and medium properties, it is possible to create a refractive index variation that can be identified with . Starting from a perturbative solution to a generalized Hopfield model for the medium described by an , we provide estimates for the number of photons generated by the time-dependent spacetime. The simplest example is that of a uniformly varying that therefore describes the Robertson–Walker metric, i.e. a cosmological expansion. The number of photon pairs generated in experimentally feasible conditions appears to be extremely small. However, large photon production can be obtained by periodically modulating the medium and thus resorting to a resonant enhancement similar to that observed in the dynamical Casimir effect. Curiously, the spacetime metric in this case closely resembles that of a gravitational wave. Motivated by this analogy, we show that a periodic gravitational wave can indeed act as an amplifier for photons. The emission for an actual gravitational wave will be very weak but should be readily observable in the laboratory analogue
Spectral properties for the Klein-Gordon Hamiltonian in charged black hole backgrounds
Full text linkCharged massive scalar fields on charged black hole backgrounds are investigated through methods of spectral analysis in Krein spaces. We consider, on the three charged black hole backgrounds (Nariai, Reissner-Nordström, ultracold-II) taken into account, a necessary condition for the existence of complex eigenvalues. We show that even if it is satisfied, in two cases (Nariai and ultracold-II), by direct calculation, they actually cannot exist. In both cases, the Klein paradox occurs without restriction on the parameters. In the third case, the condition for their existence is shown to coincide with the condition, allowing the quantum discharge phenomenon associated with the Klein paradox. We also clarify the role of “classical potentials,” which appear in the physical literature on the subject, giving rise to the so-called level-crossing appearing in semiclassical calculations, and we comment on problems occurring in quantum field theory in the presence of complex eigenvalues
Analogous Hawking Effect: S-Matrix and Thermofield Dynamics
Full text linkWe consider the full S-matrix in the scattering giving rise to analogous Hawking radiation in dispersive media. We show the general structure of the scattering in the weak dispersion approximation and discuss some unnoticed features of the primary process, with a possible generalization of the phenomenology of the Hawking effect. In particular, we stress that the Hawking particle and its antiparticle partner a priori could also be produced with different rates. We provide a general parameterization of the S-matrix, adopting the Iwasawa decomposition for the matrix itself. Then, we assume that a perturbative structure in a suitable sense is allowed and display the corresponding expansion. In connection with the general structure of the S-matrix at the leading order, we also consider the thermofield dynamics (TFD) framework and show that the TFD picture is still available, with a doubling of the degrees of freedom emerging in a natural way, as for the astrophysical black hole case. Furthermore, we show that particles on the thermal vacuum can be identified with real particles appearing in the scattering
Black holes and the third law of thermodynamics
No full textWe discuss in the framework of black hole thermodynamics some aspects relative to the third law in the case of black holes of the Kerr-Newman family. In the light of the standard proof of the equivalence between the unattainability of the zero temperature and the entropic version of the third law it is remarked that the unattainability has a special character in black hole thermodynamics. Also the zero temperature limit which obtained in the case of very massive black holes is discussed and it is shown that a violation of the entropic version in the charged case occurs. The violation of the Bekenstein-Hawking law in favour of zero entropy S_E=0 in the case of extremal black holes is suggested as a natural solution for a possible violation of the second law of thermodynamics. Thermostatic arguments in support of the unattainability are explored, and for extremal black holes is shown to be again a viable solution. The third law of black hole dynamics by W.Israel is then interpreted as a further strong corroboration to the picture of a discontinuity between extremal states and non-extremal ones
Hawking effect in dielectric media and the Hopfield model
Full text linkWe consider the so-called Hopfield model for the electromagnetic field in a dielectric dispersive medium in a framework in which one allows a space-time dependence of microscopic parameters, aimed at a phenomenological description of a space-time varying dielectric perturbation induced by means of the Kerr effect. We discuss the analogue Hawking effect by introducing a simplified model which avoids some difficulties which characterize in the full Hopfield model, still keeping the same dispersion relation. Our main result is an analytical calculation of the spontaneous thermal emission in the single-branch case, which is provided nonperturbatively for the first time in the framework of dielectric black holes. A universal mechanism for thermality which is shared both by optical black holes and acoustic black holes is also pointed out
Quantum instability for charged scalar particles on charged Nariai and ultracold black hole manifolds
No full textQuantum Instability for Charged Particles on Charged Nariai Black Hole Manifold: Exact 4D Results for Black Hole Discharge Phenomenon
No full textPerturbative Approach to Analog Hawking Radiation in dielectric media in subcritical regime
Full text linkWe take into account the subcritical case for dielectric media by exploiting
an approximation allowing us to perform perturbative analytical calculations
and still not implying low dispersive effects. We show that in the background
of a specific soliton-like solution, pair-creation occurs and can display a
thermal behaviour governed by an effective temperature. The robustness of the
approach is also corroborated by the analysis of the -model related
to the standard Hopfield model, for which analogous results are obtained.Comment: 22 pages, 6 figure
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