The Measure Preserving Isometry Groups of Metric Measure Spaces

Bochner’s theorem says that if $M$ is a compact Riemannian manifold with negative Ricci curvature, then the isometry group $\mathrm{Iso}(M)$ is finite. In this article, we show that if $(X,d,m)$ is a compact metric measure space with synthetic negative Ricci curvature in Sturm’s sense, then the measure preserving isometry group $\mathrm{Iso}(X,d,m)$ is finite. We also give an effective estimate on the order of the measure preserving isometry group for a compact weighted Riemannian manifold with negative Bakry-'Emery Ricci curvature except for small portions.