Polyhedral surfaces in anti-de Sitter (2+1)-spacetimes
Roman Prosanov
TL;DR
This work solves polyhedral Alexandrov–Weyl-type questions for GHMC anti-de Sitter (2+1)-spacetimes by realizing concave hyperbolic cone-metrics on a genus g ≥ 2 surface as future-convex bent Cauchy surfaces inside a spacetime with prescribed left holonomy, and by realizing two cone-metrics simultaneously as a future- and past-convex pair of bent surfaces. The key technique is a continuity method implemented via blow-ups of deformation spaces and a geometric transition between AdS and Minkowski geometries, leveraging a sharp intrinsic-metric map that ties surface geometry to cone-metric data. Central to the construction are bent surfaces (a relaxed, polyhedral notion) and a K-surface foliation, enabling control of degenerations and enabling properness arguments that yield existence and local uniqueness in a strong neighborhood of zero cone-metrics. The results advance the understanding of rigidity for convex-like slices in AdS spacetimes, connect Teichmüller-theoretic data to spacetime geometry through earthquake theory, and showcase the efficacy of projective-geometric methods (transitions, blow-ups) in Lorentzian 3-manifold geometry with potential implications for quantum gravity models and holographic correspondences in low dimensions.
Abstract
We first prove that given a Fuchsian representation $ρ_\circ: π_1S \ra {\rm PSL}(2,\R)$, where $S$ is a closed oriented surface of genus $\geq 2$, any hyperbolic cone-metric on $S$ with cone-angles $>2π$ isometrically embeds as a future-convex bent Cauchy surface in a globally hyperbolic maximal Cauchy compact (GHMC) anti-de Sitter (2+1)-spacetime whose left representation is $ρ_\circ$. Second, we show that given any two such cone-metrics, there exists a GHMC anti-de Sitter (2+1)-spacetime in which the cone-metrics embed simultaneously, one as a future-convex bent Cauchy surface and one as a past-convex. Furthermore, in both cases we establish that such a spacetime and embeddings are unique provided that the cone-metrics are sufficiently small.
