Aspects of Generalized Entropy and Quantum Null Energy Condition by Arvin Shahbazi-Moghaddam a Dissertation Submitted in Partial
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Aspects of Generalized Entropy And Quantum Null Energy Condition by Arvin Shahbazi-Moghaddam A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Raphael Bousso, Chair Professor Petr Hoˇrava Professor Nicolai Reshetikhin Summer 2020 Aspects of Generalized Entropy And Quantum Null Energy Condition Copyright 2020 by Arvin Shahbazi-Moghaddam 1 Abstract Aspects of Generalized Entropy And Quantum Null Energy Condition by Arvin Shahbazi-Moghaddam Doctor of Philosophy in Physics University of California, Berkeley Professor Raphael Bousso, Chair There is a deep connection between entanglement and geometry in quantum gravity. One manifestation of this connection is through the generalized entropy: the sum of the area of Cauchy-dividing surfaces in Planck units and the von Neumann entropy of the fields on one side of the surface. The generalized entropy is expected to satisfy fundamental thermody- namical conditions which in certain limits result in quantum field theory (QFT) inequalities relating the energy density and the shape derivatives of the von Neumann entropy, most notably the quantum null energy condition (QNEC). This dissertation is devoted to study- ing various aspect of the generalized entropy, the QNEC, and other information-theoretic aspects of QFT. First, we will use the QNEC to demonstrate the locality of the logarithm of the vacuum density matrix in certain regions of any holographic conformal field theory (CFT). We will then holographically prove the QNEC in general curved spacetime of less than six spacetime dimensions. Next, we will demonstrate a certain limit of the QNEC where an equality between certain components of the stress tensor and the second shape derivative of von Neumann entropy emerges. We will then focus on the study of generalized entropy. Within the AdS/CFT framework, we find a microscopic description for the generalized en- tropy of black holes using a geometric construction. We then apply this construction to extremal surface in AdS, which constitutes the bulk dual of the Connes cocycle flow on the boundary CFT. Finally, we use propose a novel lower bound on the total energy of spacetime involving the generalized entropy on certain light-sheets. i To my parents, Afsaneh and Ario, and to my sister, Arezou ii Contents Contents ii List of Figures v 1 Introduction 1 2 Local Modular Hamiltonians from the Quantum Null Energy Condition 4 2.1 Introduction and Summary . 4 2.2 Main Argument . 6 2.3 Holographic Calculation . 9 2.4 Discussion . 11 3 The Quantum Null Energy Condition, Entanglement Wedge Nesting, and Quantum Focusing 14 3.1 Introduction and Summary . 14 3.2 Entanglement Wedge Nesting . 16 3.3 Connection to Quantum Focusing . 25 3.4 Discussion . 32 4 Energy is Entanglement 36 4.1 Introduction . 36 4.2 Setup and Conventions . 39 4.3 Null Deformations and Perturbative Geometry . 46 4.4 Non-Perturbative Bulk Geometry . 49 4.5 Non-Null Deformations . 55 4.6 Discussion . 58 5 Entropy Variations and Light Ray Operators from Replica Defects 63 5.1 Introduction . 63 5.2 Replica Trick and the Displacement Operator . 68 5.3 Towards saturation of the QNEC . 71 ^ 5.4 Contribution of T++ ............................... 73 5.5 Higher order variations of vacuum entanglement . 76 iii 5.6 Near Vacuum States . 79 5.7 Discussion . 82 6 Ignorance is Cheap: From Black Hole Entropy To Energy-Minimizing States In QFT 85 6.1 Introduction and Summary . 85 6.2 Classical coarse-graining of black hole states . 87 6.3 Semiclassical coarse-graining of black hole states . 91 6.4 Quantum field theory limit of coarse-grained quantum gravity states . 97 6.5 Existence of coarse-graining states in QFT limit . 101 6.6 Discussion . 103 7 Gravity Dual of Connes Cocycle Flow 109 7.1 Introduction . 109 7.2 Connes Cocycle Flow . 111 7.3 Kink Transform . 118 7.4 Bulk Kink Transform = Boundary CC Flow . 123 7.5 Predictions . 129 7.6 Discussion . 132 8 Quantum Information Bound on the Energy 142 8.1 Introduction . 142 8.2 Classical Penrose Inequality . 144 8.3 Violation by Quantum Effects . 146 8.4 Quantum Penrose Inequality . 151 8.5 Evidence for the Quantum Penrose Inequality . 156 8.6 Alternative Proposals . 163 8.7 Quantum Penrose Inequality in Anti-de Sitter Space . 167 8.8 Classical and Non-gravitational Limits . 170 8.9 Cosmic Censorship Conjecture . 171 A Appendix 174 A.1 Notation and Definitions . 174 A.2 Surface Variations . 178 A.3 z-Expansions . 180 A.4 Details of the EWN Calculations . 182 A.5 The d = 4 Case . 184 A.6 Connections to the ANEC . 187 A.7 Free and Weakly-Interacting Theories . 190 A.8 Modified Ward identity . 195 A.9 Analytic Continuation of a Replica Three Point Function . 197 A.10 Explicit Calculation of c(2) ............................ 202 iv A.11 Explicit Calculation of γ(1) ............................ 204 A.12 Calculating Fn .................................. 206 A.13 Free Field Theories and Null Quantization . 209 A.14 Ant Conjecture and Properties of Energy Minimizing States . 211 A.15 Null Limit of the Kink Transform . 217 A.16 (Quantum) Trapped Surfaces in the Schwarzschild Geometry . 220 A.17 Perturbative Construction of Q-screens . 225 Bibliography 228 v List of Figures 2.1 This image depicts a section of the plane u = t − x = 0. The region R is defined to be one side of a Cauchy surface split by the codimension-two entangling surface @R = f(u = 0; v = V (y); y)g. The dashed line corresponds to a flat cut of the null plane. 5 3.1 Here we show the holographic setup which illustrates Entanglement Wedge Nest- ing. A spatial region A1 on the boundary is deformed into the spatial region i A2 by the null vector δX . The extremal surfaces of A1 and A2 are connected by a codimension-one bulk surface M (shaded blue) that is nowhere timelike by EWN. Then the vectors δX¯ µ and sµ, which lie in M, have nonnegative norm. 17 4.1 Most of our work concerns the variations of entanglement entropy for the yellow region R whose boundary @R lies on the null plane u = 0. The entangling surface is specified by the function V (y). 40 4.2 By restricting attention to z < z∗ the geometry is close to pure AdS, and we can ¯ solve for δX perturbatively. All of the z < z∗ data imprints itself as boundary conditions at z = z∗. We show that these boundary conditions are unimportant for our analysis, which means that a perturbative calculation is enough. 50 5.1 We consider the entanglement entropy associated to a spatial subregion R. The entangling surface lies along x− = 0 and x+ = X+(y). In this work, we study the dependence of the entanglement entropy on the profile X+(y). 64 5.2 The answer for the defect four point function Fn upon analytic continuation to n = 1. We find that there are two insertions of half-averaged null energy ^ operators, E−, as well as two insertions of E+. Note that strictly speaking, in (5.5.3), the half-averaged null energy operators are inserted in the right Rindler wedge, but by CRT invariance of the vacuum, we can take the half-averaged null energy operators to lie in the left Rindler wedge instead, as in the figure. 78 5.3 For near vacuum states, the insertions of displacement operators limit to two ^ insertions of the averaged null energy operators E+. 81 6.1 Penrose diagram of a black hole formed from collapse in Anti-de Sitter space, showing a minimar surface σ and its outer wedge OW [σ] with Cauchy surface Σ. 88 vi 6.2 Coarse-graining behind a Killing horizon. Any cut V0 can be viewed as a quantum marginally trapped surface in the limit as G ! 0. The state ρ>V0 on the Cauchy surface Σ of the outer wedge is held fixed. The coarse-grained geometry is the − original geometry. The stationary null surface Nk is the past of V0 on the Killing horizon. The coarse-grained quantum state demanded by our proposal lives on − Nk [ σ [ Σ. We identify the properties the state must have, and we show that the Ceyhan and Faulkner \ant states" satisfy these. 97 6.3 The spacetime region associated to the interval V < v < V0 on the null surface for which all observables in the algebra should register vacuum values in the coarse-graining state. 99 6.4 We would like to fix the data on N−l(ti) (green thick line), while coarse-graining in the interior of the QMT surface. Simple data in the boundary region t > ti fixes the causal wedge C[ti] and thus fixes only a portion of N−l(ti). In order to fix all of N−l(ti) one must allow for sources that remove the excitations (red arrows) that enter the black hole after σ; this can cause the causal wedge to grow to include N−l. In the coarse-graining set F, the simple data must agree for all allowed sources. 105 6.5 The left stretch is a classical analogue of the CF flow that generalizes it to non- trivial geometries. Left: The null surface Nk split by the marginally trapped − surface σ. Middle: The affine parameter is rescaled on Nk but held fixed on + Nk . This is the same initial data in nonaffine parametrization. Right: The two pieces are glued back together, treating the new parameter as affine. This yields inequivalent initial data. 108 7.1 Kink transform. Left: a Cauchy surface Σ of the original bulk M.