Real Time Correlations and Complexified Horizons

Abstract

We construct black hole saddles dual to real-time/Schwinger-Keldysh (SK) path integrals with arbitrary splits of the thermal density matrix generalizing the holographic SK prescription in \cite{Glorioso:2018mmw}. Using a scalar probe on the AdS Schwarzschild black brane as an example, we demonstrate how KMS properties of the boundary correlators naturally derive from these geometries. As deforming the boundary time contour is equivalent to the action of half sided modular transformation, these saddles can be used to compute higher point modular transformed correlators using a well controlled bulk perturbation theory. An interesting relation between these saddles and the more familiar eternal geometries, and the respective generators of time translation on them is described. Inspired from recent discussions on algebras of observables in gravity, we motivate that classical ensembles of such geometries with different amount of modular transformations should be promoted to genuine configurations of the bulk geometry. In particular, this is argued to imply the existence of additional classical moduli in the boundary open EFT dual to the exterior dynamics, and via fluid gravity correspondence, in the fluctuating hydrodynamics of the boundary. Finally, a Lorentzian version of the Kontsevich-Segal conditions is verified for all these geometries.