Revista Matemática Iberoamericana
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Published online: 2008-12-31
Large-scale Sobolev inequalities on metric measure spaces and applicationsRomain Tessera (1) Université Paris-Sud, Orsay, France
For functions on a metric measure space, we introduce a notion of "gradient at a given scale''. This allows us to define Sobolev inequalities at a given scale. We prove that satisfying a Sobolev inequality at a large enough scale is invariant under large-scale equivalence, a metric-measure version of coarse equivalence. We prove that for a Riemmanian manifold satisfying a local Poincaré inequality, our notion of Sobolev inequalities at large scale is equivalent to its classical version. These notions provide a natural and efficient point of view to study the relations between the large time on-diagonal behavior of random walks and the isoperimetry of the space. Specializing our main result to locally compact groups, we obtain that the $L^p$-isoperimetric profile, for every $1\leq p\leq \infty$ is invariant under quasi-isometry between amenable unimodular compactly generated locally compact groups. A qualitative application of this new approach is a very general characterization of the existence of a spectral gap on a quasi-transitive measure space $X$, providing a natural point of view to understand this phenomenon.
Keywords: Large-scale analysis on metric spaces, coarse equivalence, symmetric random walks on groups, Sobolev inequalities, isoperimetry
Tessera Romain: Large-scale Sobolev inequalities on metric measure spaces and applications. Rev. Mat. Iberoam. 24 (2008), 825-864. doi: 10.4171/RMI/557