Quantitative marked length spectrum rigidity
Karen Butt
TL;DR
This work develops a quantitative version of marked length spectrum rigidity in negative curvature by combining Liouville-current analysis, cross-ratio controls, and the Besson–Courtois–Gallot framework. It establishes explicit ε-dependent volume and derivative bounds for the BCG map when MLS of two manifolds are ε-close, leading to near isometry in higher dimensions. A parallel argument for compact negatively curved surfaces, using Otal and Pugh techniques, yields a distance-preserving correspondence in the limit. Collectively, the results provide a rigorous, quantitative stability theory for marked length spectrum rigidity and its geometric consequences.
Abstract
We consider a closed Riemannian manifold $M$ of negative curvature and dimension at least 3 with marked length spectrum sufficiently close (multiplicatively) to that of a locally symmetric space $N$. Using the methods of Hamenstädt, we show the volumes of $M$ and $N$ are approximately equal. We then show the Besson-Courtois-Gallot map $F: M \to N$ is a diffeomorphism with derivative bounds close to 1 and depending on the ratio of the two marked length spectrum functions. Thus, we refine the results of Hamenstädt and Besson-Courtois-Gallot, which show $M$ and $N$ are isometric if their marked length spectra are equal. We also prove a similar result for compact negatively curved surfaces using the methods of Otal together with a version of the Gromov compactness theorem due to Pugh.
