Nonamenable subforests of multi-ended quasi-pmp graphs
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.
Keywords
Cite
@article{arxiv.2211.07908,
title = {Nonamenable subforests of multi-ended quasi-pmp graphs},
author = {Ruiyuan Chen and Grigory Terlov and Anush Tserunyan},
journal= {arXiv preprint arXiv:2211.07908},
year = {2025}
}
Comments
36 pages, 3 figures. Improved and revised results, changed the exposition of the cluster graphing construction, polished presentation