Holographic BCFTs and Communicating Black Holes

TL;DR

This paper explores the holographic duality between BCFTs and AdS space with branes, analyzing entanglement entropy and black hole communication, revealing a Page curve and a spectral gap in boundary operators.

Contribution

It provides a detailed computation of entanglement entropy in holographic BCFTs at finite and zero temperature, extending the AdS/BCFT correspondence and analyzing boundary operator spectra.

Findings

Matching entanglement entropy calculations on gravity and field theory sides.

Identification of a spectral gap in boundary condition changing operators.

Discovery of different gravitational dual geometries depending on operator dimensions.

Abstract

We study the AdS/BCFT duality between two-dimensional conformal field theories with two boundaries and three-dimensional anti-de Sitter space with two Karch-Randall branes. We compute the entanglement entropy of a bipartition of the BCFT, on both the gravity side and the field theory side. At finite temperature this entanglement entropy characterizes the communication between two braneworld black holes, coupled to each other through a common bath. We find a Page curve consistent with unitarity. The gravitational result, computed using double-holographically realized quantum extremal surfaces, matches the conformal field theory calculation. At zero temperature, we obtain an interesting extension of the AdS$_3$/BCFT$_2$ correspondence. For a central charge $c$, we find a gap $(\frac{c}{16},\frac{c}{12})$ in the spectrum of the scaling dimension $\Delta_{\text{bcc}}$ of the boundary condition changing operator (which interpolates mismatched boundary conditions on the two boundaries of the BCFT). Depending on the value of $\Delta_{\text{bcc}}$, the gravitational dual is either a defect global AdS$_3$ geometry or a single sided black hole, and in both cases there are two Karch-Randall branes.