Dissecting the ensemble in JT gravity

TL;DR

This paper analyzes how JT gravity encodes bulk and boundary correlators via an ensemble average, and shows that late-time behavior and non-decay arise from wormholes that connect distant regions. By organizing bulk correlation contributions into simple geometric classes and matching them to random-matrix predictions, the authors reproduce ensemble-averaged correlators and motivate a bulk reconstruction framework. They then construct more microscopic descriptions by adding branes (eigenbranes and eigenvector branes) that realize alpha-states, enabling observables to factorize in a single quantum system. The work also probes the large-distance behavior of bulk correlators with conformal matter and extremal fields, revealing plateau-like remnants and potential bulk puzzles. Overall, the paper clarifies when gravity computes ensemble averages and how branes can encode microstructure, while highlighting open issues in Lorentzian interpretation and higher-dimensional generalization.

Abstract

We calculate bulk and boundary correlators in JT gravity by summing over geometries. The answers are reproduced by computing suitable ensemble averages of correlators of chaotic quantum systems. We then consider bulk correlators at large spatial separations and find that semiclassical decay eventually makes way for erratic oscillations around some nonzero answer. There is no cluster decomposition because of wormholes connecting distant regions. We construct more microscopic versions of JT gravity which are dual to a single quantum system by including a set of branes in the gravitational theory the data of which describes the Hamiltonian of the dual system. We focus on the bulk description of eigenstates which involves end of the world branes and we explain how observables factorize due to geometries connecting to these branes.