Christoph Sieling | Searcharxiv

arXiv2026

Flat Holography & Holographic Renormalization: Scalar Field

We adapt the Hamilton-Jacobi method of holographic renormalization to scalar field theories in Minkowski spacetime with scattering boundary conditions. The approach yields a flat-space holographic dictionary in which the expectation value of a dual operator is given by the renormalized canonical momentum. The source of the operator is imposed as a Dirichlet condition in a radial timelike foliation of the bulk theory and corresponds to the scattering data appearing in the Arefeva-Faddeev-Slavnov generating functional. We initiate a study of massive scalars and interacting fields within this formalism and we comment on extensions to different bulk theories and backgrounds.

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arXiv2025

A Holographic prescription for generalized Schwinger-Keldysh contours

We provide a holographic prescription to compute real-time thermal correlators with arbitrary operator ordering. In field theory, these correlation functions are captured by a multi-fold Schwinger-Keldysh time contour. We propose a holographic dual for these contours, which generalizes the gravitational Schwinger-Keldysh geometry previously advocated in the literature. Our geometry consists of multiple AdS-black holes glued together at the future and past horizons, with matching conditions determined by unitarity and the KMS condition. As a proof of concept, we solve for a probe scalar field in this geometry and compute bulk-bulk and bulk-boundary propagators, in terms of which we evaluate the 4-point functions at tree-level. We show that in perturbation theory, the lowest-order diagrams that contribute non-trivially to the out-of-time order four-point function are exchange diagrams which explore the full four-fold geometry. Furthermore, these diagrams reduce to a simple factorized expression. We propose a conjecture on the structure of higher order observables and provide a partial proof by studying a subset of the contributing diagrams.

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