Information radiation in BCFT models of black holes

TL;DR

This paper models evaporating black holes using BCFT holographic systems, analyzing entanglement entropy evolution and revealing information radiation processes even in thermal equilibrium.

Contribution

It introduces a BCFT-based holographic framework for black hole evaporation, highlighting the role of boundary-to-bulk degrees of freedom ratio in entanglement dynamics.

Findings

Entanglement entropy increases until the Page time.

A phase transition occurs where the radiation's entanglement wedge includes the black hole interior.

Information about the black hole is radiated without energy loss, even in thermal equilibrium.

Abstract

In this note, following [arXiv:1905.08255, arXiv:1905.08762, arXiv:1908.10996], we introduce and study various holographic systems which can describe evaporating black holes. The systems we consider are boundary conformal field theories for which the number of local degrees of freedom on the boundary ($c_{bdy}$) is large compared to the number of local degrees of freedom in the bulk CFT ($c_{bulk}$). We consider states where the boundary degrees of freedom on their own would describe an equilibrium black hole, but the coupling to the bulk CFT degrees of freedom allows this black hole to evaporate. The Page time for the black hole is controlled by the ratio $c_{bdy}/c_{bulk}$. Using both holographic calculations and direct CFT calculations, we study the evolution of the entanglement entropy for the subset of the radiation system (i.e. the bulk CFT) at a distance $d > a$ from the boundary. We find that the entanglement entropy for this subsystem increases until time $a + t_{Page}$ and then undergoes a phase transition after which the entanglement wedge of the radiation system includes the black hole interior. Remarkably, this occurs even if the radiation system is initially at the same temperature as the black hole so that the two are in thermal equilibrium. In this case, even though the black hole does not lose energy, it "radiates" information through interaction with the radiation system until the radiation system contains enough information to reconstruct the black hole interior.