On moduli spaces of uniformly negatively curved metrics

Abstract

Let $\Neg(X)$ denote the space of complete Riemannian metrics with uniformly negative curvature on a surface $X$, equipped with the intrinsic uniform $C^2$ topology. Let $\mathcal M(X)=\Neg(X)/\Diff(X)$ be the corresponding moduli space, with the quotient topology. We construct elementary locally constant functionals on $\mathcal{M}(X)$, with values in finite symmetric products of $\{0,1\}$, based on geodesic string counts. As an upshot we show that $\mathcal{M}(\mathbb{R}\times S^1)$ is disconnected. This is perhaps surprising: the two metrics we separate are joined by an explicit path of metrics with constant curvature $-1$. The point is that this path is only continuous in the weak Whitney topology. More generally, if $X$ is a finite-type surface of hyperbolic type with $n$ punctures, then the pure moduli space has at least $2^n$ connected components, while $\mathcal{M}(X)$ has at least $n+1$ connected components.

Title change, significant revision due to a gap in the previous version, techniques are now more elementary, 11 pages