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arXiv:1711.08505

Entanglement Entropy for D3-, M2- and M5-brane backgrounds

Edward Quijada, Henrique Boschi-Filho

Published Nov 22, 2017• 2 citations
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Abstract

In the context of the gauge/gravity duality applications, we study and compute the entanglement entropy of gauge theories corresponding to string/M theories on D3-, M2- and M5-brane backgrounds. This is achieved using the Ryu-Takayanagi formula. We obtain the entanglement entropy for the general cases of the D3-, M2- and M5-brane backgrounds and also for the near horizon AdS limit, as well as the non-conformal flat space limit in each case.

DOI
10.48550/arxiv.1711.08505

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In the context of the gauge/gravity duality applications, we study and compute the entanglement entropy of gauge theories corresponding to string/M theories on D3-, M2- and M5-brane backgrounds. This is achieved using the Ryu-Takayanagi formula. We obtain the entanglement entropy for the general cases of the D3-, M2- and M5-brane backgrounds and also for the near horizon AdS limit, as well as the non-conformal flat space limit in each case.
We propose a new action for entanglement entropy in the framework of the AdS 3 / CFT 2 correspondence. This action is constructed directly from the entanglement entropy of the CFT 2 , and we show that the Einstein equations of AdS 3 gravity can be derived from it. In the near-coincidence limit, using Riemann normal coordinates, the action reduces to a string world-sheet action in a curved background that naturally includes the symmetric spacetime metric, an antisymmetric Kalb-Ramond field, and a dilaton. The Kalb-Ramond field gives rise to a string charge density, from which we demonstrate that bit threads can be exactly reproduced. This correspondence provides a clear physical interpretation of bit threads. Exploiting this correspondence, we establish explicit relations between the emergent string world sheet and the Ryu-Takayanagi (RT) surface, providing new insights into entanglement entropy. In particular, entanglement entropy can be computed from open string charge, while Bekenstein-Hawking entropy arises from closed string charge through open-closed string duality. These results suggest a unified picture in which the Susskind-Uglum conjecture, open-closed string duality, and the ER = EPR proposal emerge as equivalent manifestations of the same underlying principle. Finally, we propose a quantization of the RT surface, pointing to a possible connection with loop quantum gravity that refines Wall’s conjecture.
In this Dissertation, different aspects of holographic entanglement entropy are explored. In quantum information theory, entanglement is a useful resource needed to perform quantum operations. Entanglement entropy quantifies this resource and even if computable in quantum field theories, it is quite hard to calculate explicitly. However, in the context of gauge/gravity duality, (holographic) entanglement entropy was proposed by Ryu and Takayanagi (RT) to be captured by the area of a minimal surface in Anti DeSitter (AdS) space, which is extremely simple to compute. We begin by using the holographic dictionary to derive the RT formula. This is done by first considering smooth bulk geometries which are dual to n copies of the boundary geometry glued in a particular way. The action of these geometries computes the Renyi entropies S_n for any integer n. We give a prescription to analytically continue the action to non-integer n and argue that, as n goes to 1,S_1, the entanglement entropy, is given by the area of a minimal surface, reproducing the RT conjecture. That is, we reduced the RT proposal to the equality between bulk and boundary partition functions, a standard entry in the dictionary. We then generalize the previous formalism to account for corrections due to bulk quantum fields (1/N corrections in the boundary). This allows us to derive a new formula: boundary entanglement entropy is given by the area of the minimal surface plus bulk entanglement entropy. This extends RT beyond the planar limit and we present several predictions of the proposal. Our exploration of holographic entanglement entropy continues by considering different states: by comparing the quantum corrected entropy for nearby states we obtain the modular hamiltonian operator in bulk perturbation theory. From this expression of the modular hamiltonian, we derive that relative entropy is bulk relative entropy and that the modular flow is the bulk modular flow.
We use gauge-gravity duality to compute entanglement entropy in a non-conformal background with an energy scale Λ. At zero temperature , we observe that entanglement entropy decreases by raising Λ. However, at finite temperature , we realize that both Λ T and entanglement entropy rise together. Comparing entanglement entropy of the non-conformal theory, S A ( N ) , and of its conformal theory at the UV limit, S A ( C ) , reveals that S A ( N ) can be larger or smaller than S A ( C ) , depending on the values of Λ and T .
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We define a generalized entanglement measure in the context of AdS3_33​/CFT2_22​. Compared to the ordinary entanglement entropy between spatial degrees of freedom dual to the area of the Ryu-Takayanagi surface, we take into account both entanglement between spatial degrees of freedom as well as between different fields of the boundary CFT. We then calculate this generalized entanglement measure in a thermal state dual to the BTZ black hole in the setting of the D1/D5 system at and close to the orbifold point. We find that the entanglement entropy defined in this way is dual to the length of a geodesic with non-zero winding number. Such geodesics probe the entire bulk geometry, including regions known as entanglement shadows which are not reached by any Ryu-Takayanagi surface. This allows us to describe regions close to the black hole horizon in the one-sided black hole and the wormhole growth in the case of a two-sided black hole from entanglement data in the boundary field theory, leading us to propose that entanglement is in fact enough to reconstruct the full BTZ geometry from boundary data.