Journal Home Page Cumulative Index List of all Volumes Complete Contentsof this Volume Previous Article Journal of Lie Theory 28 (2018), No. 3, 619--642Copyright Heldermann Verlag 2018 The Volume of Complete Anti-de Sitter 3-Manifolds Nicolas Tholozan Dép. de Mathématiques et Applications, Ecole Normale Supérieure, PSL Research University, 45 rue d'Ulm, 75005 Paris, France nicolas.tholozan@ens.fr [Abstract-pdf] \def\SO{\mathop{\rm SO}\nolimits} Up to a finite cover, closed anti-de Sitter $3$-manifolds are quotients of $\SO_0(2,1)$ by a discrete subgroup of $\SO_0(2,1) \times \SO_0(2,1)$ of the form $j{\times}\rho(\Gamma)$, where $\Gamma$ is the fundamental group of a closed oriented surface, $j$ a Fuchsian representation and $\rho$ another representation which is strictly dominated'' by $j$.\par Here we prove that the volume of such a quotient is proportional to the sum of the Euler classes of $j$ and $\rho$. As a consequence, we obtain that this volume is constant under deformation of the anti-de Sitter structure. Our results extend to (not necessarily compact) quotients of $\SO_0(n,1)$ by a geometrically finite'' subgroup of $\SO_0(n,1) \times \SO_0(n,1)$. Keywords: Anti-de Sitter, (G,X)-structures, Clifford-Klein forms, volume of 3-manifolds. MSC: 53C50, 22E40 [ Fulltext-pdf  (326  KB)] for subscribers only.