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Gravitation
About: Gravitation is a research topic. Over the lifetime, 29306 publications have been published within this topic receiving 821510 citations.
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TL;DR: In this article, the authors examined gravity theories derived from a gravitational lagrangian and showed that they are conformally equivalent to general relativity plus a scalar-field matter source with a particular self-interaction potential.
588 citations
01 Jan 2009
TL;DR: In this article, it was shown that at the level of linear response the low-frequency limit of a strongly coupled field theory at finite temperature is determined by the horizon geometry of its gravity dual, i.e., by the "membrane paradigm" fluid of classical black hole mechanics.
Abstract: We show that at the level of linear response the low-frequency limit of a strongly coupled field theory at finite temperature is determined by the horizon geometry of its gravity dual, i.e., by the ‘‘membrane paradigm’’ fluid of classical black hole mechanics. Thus, generic boundary theory transport coefficients can be expressed in terms of geometric quantities evaluated at the horizon. When applied to the stress tensor this gives a simple, general proof of the universality of the shear viscosity in terms of the universality of gravitational couplings, and when applied to a conserved current it gives a new general formula for the conductivity. Away from the low-frequency limit the behavior of the boundary theory fluid is no longer fully captured by the horizon fluid even within the derivative expansion; instead, we find a nontrivial evolution from the horizon to the boundary. We derive flow equations governing this evolution and apply them to the simple examples of charge and momentum diffusion.
588 citations
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TL;DR: A new parameter-free unification of micro- and macrodynamics is constructed and gravitational measures for reducing macroscopic quantum fluctuations of the mass density are applied to lead to classical trajectories in the Macroscopic limit of translational motion.
Abstract: This paper adopts the hypothesis that the absence of macroscopic quantum fluctuations is due to a certain universal mechanism. Such a mechanism has recently been proposed by Ghirardi et al. [Phys. Rev. D 34, 470 (1986)], and here we recapitulate a compact version of it. K\'arolyh\'azy [Nuovo Cimento 52, 390 (1966)] showed earlier the possible role of gravity and, along this line, we construct here a new parameter-free unification of micro- and macrodynamics. We apply gravitational measures for reducing macroscopic quantum fluctuations of the mass density. This model leads to classical trajectories in the macroscopic limit of translational motion. For massive objects, unwanted macroscopic superpositions of quantum states become destroyed in very short times. The relation between state-vector and density-operator formalisms has also been discussed. We only anticipate the need for elaborating characteristic predictions of the model in the region separating micro- and macroscopic properties.
587 citations
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TL;DR: In this paper, a detailed quantization of the pure Einstein-Maxwell geometrodynamics is presented, which brings to light some of the most important properties to be expected for quantized geometrodynamics and assess whether this theory can contribute anything to the understanding of the elementary particle problem.
586 citations
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TL;DR: The theory of holographic superconductors has been introduced in this article, where a dual description using gauge/gravity duality is used to describe the properties of a superconductor.
Abstract: These lectures give an introduction to the theory of holographic superconductors These are superconductors that have a dual gravitational description using gauge/gravity duality After introducing a suitable gravitational theory, we discuss its properties in various regimes: the probe limit, the effects of backreaction, the zero temperature limit, and the addition of magnetic fields Using the gauge/gravity dictionary, these properties reproduce many of the standard features of superconductors Some familiarity with gauge/gravity duality is assumed A list of open problems is included at the end
582 citations