### 24.11.2020 (Tuesday)

#### Free Energy from Replica Wormholes

Regular Seminar Netta Engelhardt (Massachusetts Institute of Technology)

 at: 14:30 ICroom zoom 871 9223 5980 abstract: Recent developments on the black hole information paradox have shown that Euclidean wormholes â€” so called â€œreplica wormholesâ€™â€™ can dominate the von Neumann entropy as computed by a gravitational path integral, and that inclusion of these wormholes results in a unitary Page curve. This development raises some puzzles from the perspective of factorization, and has raised questions regarding what the gravitational path integral is computing. In this talk, I will focus on understanding the relationship between the gravitational path integral and the partition function via the gravitational free energy (more generally the generating functional). A proper computation of the free energy requires a replica trick distinct from the usual one used to compute the entropy. I will show that in JT gravity there is a regime where the free energy computed without replica wormholes is pathological. Interestingly, the inclusion of replica wormholes is not quite sufficient to resolve the pathology: an alternative analytic continuation is required. I will discuss the implications of this for various interpretations of the gravitational path integral (e.g. as computing an ensemble average) and also mention some parallels with spin glasses. [please email a.held@imperial.ac.uk for zoom link or password]