A tale of two saddles

We find a new on-shell replica wormhole in a computation of the generating functional of JT gravity coupled to matter. We show that this saddle has lower action than the disconnected one, and that it is stable under restriction to real Lorentzian sections, but can be unstable otherwise. The behavior of the classical generating functional thus may be strongly dependent on the signature of allowed perturbations. As part of our analysis, we give an LM-style construction for computing the on-shell action of replicated manifolds even as the number of boundaries approaches zero, including a type of one-step replica symmetry breaking that is necessary to capture the contribution of the new saddle. Our results are robust against quantum corrections; in fact, we find evidence that such corrections may sometimes stabilize this new saddle.

Automated summary

We have discovered a new on-shell replica wormhole and shown that it has lower action than the disconnected one. The stability of this replica wormhole depends on the signature of allowed perturbations. We have also introduced a new method for computing the on-shell action of replicated manifolds and found evidence that quantum corrections can sometimes stabilize this new saddle.