Abstract: In 2017, a proposal was made for defining RT surfaces in asymptotically flat spacetimes, with the goal of computing the entanglement entropy in a putative dual theory. To avoid confusion with the usual RT prescription, the resulting surfaces are called swing surfaces. We take advantage of the flat limit of AdS/CFT to argue that swing surfaces do not compute standard entanglement entropies in the CFT; however, they do compute an information-theoretic observable closely tied to “spacelike modular flows” appearing in the study of inner horizon thermodynamics. We discuss some puzzles that this entails for inner horizons in AdS/CFT.
Based on two upcoming works, with Sabrina Pasterski and Rob Myers, and Aidan Herderschee.