Holographic BCFTs and Communicating Black Holes

Recent developments towards understanding the black hole information paradox and obtaining a page curve consistent with unitarity have relied on a non-gravitating bath coupled to black holes in AdS spacetime. The effect of switching on gravity in the bath has been argued to change the picture qualitatively, and has been studied using doubly holographic setups, where a page curve disappears. Nevertheless, a page curve-like behavior exists for a different entropy, the L/R entropy, which signifies communication between two gravitational spacetimes, exchanging information through a common boundary. Explicit calculations for L/R entropy have been performed gravitationally. In this talk I will review the situation and discuss my recent work which showed how to calculate this entropy purely from a field theory point of view, using a regularized geometry and using properties of a Boundary Conformal Field Theory (BCFT). The calculations match the gravitational expectation, and provide a purely field-theoretic interpretation of L/R entropy.(Based on 2104.07039)