The space of properly-convex structures

Abstract

Suppose $G$ is finitely generated group and $\mathcal{C}(G)$ consists of all $ρ:G\to\operatorname{PGL}(n+1,\mathbb{R})$ for which there exists a properly convex set in $\mathbb{R}\mathbb{P}^n$ that is preserved by $ρ(G)$. Then the image of $\mathcal{C}(G)$ is closed in the character variety. Suppose $G$ does not contain an infinite, normal, abelian subgroup and $\mathcal{D}(G)\subset\mathcal{C}(G)$ is the subset of holonomies of properly-convex $n$-manifolds with fundamental group $G$. Then the image $\mathcal{D}(G)$ is closed in the character variety. If $M$ is the interior of a compact $n$-manifold and $G=π_1M$ is as above, and either $M$ is closed, or $π_1M$ contains a subgroup of infinite index isomorphic to $\mathbb{Z}^{n-1}$, then $\mathcal{D}(G)$ is closed. If, in addition, $M$ is the interior of a compact manifold $N$ such that every component of $\partial N$ is $π_1$-injective, and finitely covered by a torus, then every element of $\mathcal{D}(G)$ is the holonomy of a properly-convex structure on $M$, and $\mathcal{D}(G)$ is a union of connected components of a semi-algebraic set.