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      Bulk entanglement entropy in perturbative excited states

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      SciPost Physics
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          Abstract

          We compute the bulk entanglement entropy across the Ryu-Takayanagi surface for a one-particle state in a scalar field theory in AdS _3 . We work directly within the bulk Hilbert space and include the spatial spread of the scalar wavefunction. We give closed form expressions in the limit of small interval sizes and compare the result to a CFT computation of entanglement entropy in an excited primary state at large c . Including the contribution from the backreacted minimal area, we find agreement between the CFT result and the FLM and JLMS formulas for quantum corrections to holographic entanglement entropy. This provides a non-trivial check in a state where the answer is not dictated by symmetry. Along the way, we provide closed-form expressions for the scalar field Bogoliubov coefficients that relate the global and Rindler slicings of AdS _3 .

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          Infinite conformal symmetry in two-dimensional quantum field theory

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            Some Properties of Noether Charge and a Proposal for Dynamical Black Hole Entropy

            We consider a general, classical theory of gravity with arbitrary matter fields in \(n\) dimensions, arising from a diffeomorphism invariant Lagrangian, \(\bL\). We first show that \(\bL\) always can be written in a ``manifestly covariant" form. We then show that the symplectic potential current \((n-1)\)-form, \(\th\), and the symplectic current \((n-1)\)-form, \(\om\), for the theory always can be globally defined in a covariant manner. Associated with any infinitesimal diffeomorphism is a Noether current \((n-1)\)-form, \(\bJ\), and corresponding Noether charge \((n-2)\)-form, \(\bQ\). We derive a general ``decomposition formula" for \(\bQ\). Using this formula for the Noether charge, we prove that the first law of black hole mechanics holds for arbitrary perturbations of a stationary black hole. (For higher derivative theories, previous arguments had established this law only for stationary perturbations.) Finally, we propose a local, geometrical prescription for the entropy, \(S_{dyn}\), of a dynamical black hole. This prescription agrees with the Noether charge formula for stationary black holes and their perturbations, and is independent of all ambiguities associated with the choices of \(\bL\), \(\th\), and \(\bQ\). However, the issue of whether this dynamical entropy in general obeys a ``second law" of black hole mechanics remains open. In an appendix, we apply some of our results to theories with a nondynamical metric and also briefly develop the theory of stress-energy pseudotensors.
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              Black Hole Entropy is Noether Charge

              We consider a general, classical theory of gravity in \(n\) dimensions, arising from a diffeomorphism invariant Lagrangian. In any such theory, to each vector field, \(\xi^a\), on spacetime one can associate a local symmetry and, hence, a Noether current \((n-1)\)-form, \({\bf j}\), and (for solutions to the field equations) a Noether charge \((n-2)\)-form, \({\bf Q}\). Assuming only that the theory admits stationary black hole solutions with a bifurcate Killing horizon, and that the canonical mass and angular momentum of solutions are well defined at infinity, we show that the first law of black hole mechanics always holds for perturbations to nearby stationary black hole solutions. The quantity playing the role of black hole entropy in this formula is simply \(2 \pi\) times the integral over \(\Sigma\) of the Noether charge \((n-2)\)-form associated with the horizon Killing field, normalized so as to have unit surface gravity. Furthermore, we show that this black hole entropy always is given by a local geometrical expression on the horizon of the black hole. We thereby obtain a natural candidate for the entropy of a dynamical black hole in a general theory of gravity. Our results show that the validity of the ``second law" of black hole mechanics in dynamical evolution from an initially stationary black hole to a final stationary state is equivalent to the positivity of a total Noether flux, and thus may be intimately related to the positive energy properties of the theory. The relationship between the derivation of our formula for black hole entropy and the derivation via ``Euclidean methods" also is explained.
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                Author and article information

                Journal
                SciPost Physics
                SciPost Phys.
                Stichting SciPost
                2542-4653
                2018
                September 20 2018
                : 5
                : 3
                Affiliations
                [1 ]Institute of Physics, University of Amsterdam
                [2 ]Durham University
                Article
                10.21468/SciPostPhys.5.3.024
                40503a66-37c5-4a52-a36f-6fe7b94ebbbe
                © 2018

                This work is licensed under a Creative Commons Attribution 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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