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arXiv · 1607.02575

Approximate invariance for ergodic actions of amenable groups

Michael Björklund·Alexander Fish
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Abstract

We develop in this paper some general techniques to analyze action sets of small doubling for probability measure-preserving actions of amenable groups. As an application of these techniques, we prove a dynamical generalization of Kneser's celebrated density theorem for subsets in $(\bZ,+)$, valid for any countable amenable group, and we show how it can be used to establish a plethora of new inverse product set theorems for upper and lower asymptotic densities. We provide several examples demonstrating that our results are optimal for the settings under study.

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Michael Björklund, Alexander Fish. 2016-07-09. Approximate invariance for ergodic actions of amenable groups. https://arxiv.org/abs/1607.02575

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