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arXiv · 2211.07908

Nonamenable subforests of multi-ended quasi-pmp graphs

Ruiyuan Chen·Grigory Terlov·Anush Tserunyan
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Abstract

We prove the a.e. nonamenability of locally finite quasi-pmp Borel graphs whose every component admits at least three nonvanishing ends with respect to the underlying Radon--Nikodym cocycle. We witness their nonamenability by constructing Borel subforests with at least three nonvanishing ends per component, and then applying Tserunyan and Tucker-Drob's recent characterization of amenability for acyclic quasi-pmp Borel graphs. Our main technique is a weighted cycle-cutting algorithm, which yields a weight-maximal spanning forest. We also introduce a random version of this forest, which generalizes the Free Minimal Spanning Forest, to capture nonunimodularity in the context of percolation theory.

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Ruiyuan Chen, Grigory Terlov, Anush Tserunyan. 2026-09-13. Nonamenable subforests of multi-ended quasi-pmp graphs. https://arxiv.org/abs/2211.07908

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