Finitary random interlacements and the Gaboriau–Lyons problem

The von Neumann–Day problem asks whether every non-amenable group contains a non-abelian free group. It was answered in the negative by Ol’shanskii in the 1980s. The measurable version (formulated by Gaboriau–Lyons) asks whether every non-amenable measured equivalence relation contains a non-amenabl...

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Bibliographic Details
Published in:Geometric and functional analysis 2019-06, Vol.29 (3), p.659-689
Main Author: Bowen, Lewis
Format: Article
Language:English
Subjects:
Analysis
Entropy of solution
Mathematics
Mathematics and Statistics
Random walk
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Summary:The von Neumann–Day problem asks whether every non-amenable group contains a non-abelian free group. It was answered in the negative by Ol’shanskii in the 1980s. The measurable version (formulated by Gaboriau–Lyons) asks whether every non-amenable measured equivalence relation contains a non-amenable treeable subequivalence relation. This paper obtains a positive answer in the case of arbitrary Bernoulli shifts over a non-amenable group, extending work of Gaboriau–Lyons. The proof uses an approximation to the random interlacement process by random multisets of geometrically-killed random walk paths. There are two applications: (1) the Gaboriau–Lyons problem for actions with positive Rokhlin entropy admits a positive solution, (2) for any non-amenable group, all Bernoulli shifts factor onto each other.
ISSN:1016-443X
1420-8970
DOI:10.1007/s00039-019-00494-4