Ephemeral islands, plunging quantum extremal surfaces and BCFT channels

Abstract

We consider entanglement entropies of finite spatial intervals in Minkowski radiation baths coupled to the eternal black hole in JT gravity, and the related problem involving free fermion BCFT in the thermofield double state. We show that the non-monotonic entropy evolution in the black hole problem precisely matches that of the free fermion theory in a high temperature limit, and the results have the form expected for CFTs with quasiparticle description. Both exhibit rich behaviour that involves at intermediate times, an entropy saddle with an island in the former case, and in the latter a special class of disconnected OPE channels. The quantum extremal surfaces start inside the horizon, but can emerge from and plunge back inside as time evolves, accompanied by a characteristic dip in the entropy also seen in the free fermion BCFT. Finally an entropy equilibrium is reached with a no-island saddle.

Bath deformations, islands and holographic complexity

“…See[72][73][74][75][76][77][78][79][80] and the references therein 4. See[44,57,[84][85][86] for the recent explorations of BCFT.…”

Grey-body factors, irreversibility and multiple island saddles

“…. , p, with u 0 = 0 and where |u j − u j−1 | ∆t s , 12 then R can be taken to be a subset of {A j }. The set up is shown schematically in figure 5.…”

The Spectrum of Boundary States in Symmetric Orbifolds

“…By the notation S n i (N i ) we mean permutations of n i elements starting at N i + 1 where N i = j<i n j . For example, for S 3 (5) we would generate states such as |a (678) in the twist-3 sector or |a (68) (7) in the twist-2 times untwisted sector. The second sum over S N simply makes the state invariant under permutations so that it is a well-defined orbifold state.…”

“…n = N î) and analyze the AdS/BCFT data for such states. 7 The notion of typicality will now constrain what type of representation vector r we pick. Since we pick all states to be the same, it involves understanding what a typical representation of S N looks like.…”

“…These questions are of great interest with the recent upsurge in applications of holographic boundary conformal field theory (BCFT). BCFTs have been used as examples of a gravitational system (the bulk dual of the boundary) coupled to an auxiliary bath (the ambient CFT) to study black hole evaporation and entanglement islands [1][2][3][4][5][6][7][8][9]. BCFTs have likewise seen renewed interest as examples of cosmological spacetimes (the bulk dual of the boundary) embedded in a higher-dimensional spacetime (the bulk dual of the ambient CFT) [10][11][12][13].…”