On $(2,1)$-dimensional anti-de Sitter spacetimes with convex boundary

Let $S$ be a closed oriented surface of genus at least $2$. Let $X$ be a $(2,1)$-dimensional anti-de Sitter spacetime homeomorphic to $S\times [-1,1]$ with smooth, spacelike, strongly convex boundary. By Gauss’ formula, the induced metric on each of the two components of $\mathrm{\partial }X$ has curvature $K<-1$. In this paper we address the inverse problem. We show that, for any two smooth metrics $h_{-},h_{+}$ on $S$ with curvature $K<-1$, there exists a unique, smooth anti-de Sitter metric on $X:=S\times [-1,1]$ with respect to which the boundary is locally strongly convex and has induced metric isotopic to $h_{-}$ on its past component and isotopic to $h_{+}$ on its future component. Existence has already been proven by Tamburelli. We use this result to solve affirmatively a conjecture of Mess: given any two measured laminations $l_{-},l_{+}\in {\mathcal{M}\mathcal{L}}_S$ that together fill $S$, there exists a unique $(2,1)$-dimensional, globally hyperbolic, maximal, Cauchy compact (GHMC) anti-de Sitter spacetime such that the measured bending laminations of the past and future boundary components of its convex core are respectively $l_{-}$ and $l_{+}$. Here, existence has already been proven by Bonsante–Schlenker.