The Poisson boundary of Thompson's group $T$ is not the circle

Let $\mu$ be a nondegenerate probability measure with finite entropy on a countable group $G \leq \mathrm{Homeo}_+(S^1)$ of orientation-preserving homeomorphisms of the circle acting proximally, minimally and topologically nonfreely on $S^1$. We prove that the circle $S^1$ endowed with its unique $\mu$-stationary probability measure is not the Poisson boundary of $(G,\mu)$. When $G$ is Thompson's group $T$ and $\mu$ is finitely supported, this answers a question posed by B. Deroin [Ergodic Theory Dynam. Systems, 2013] and A. Navas [Proceedings of the International Congress of Mathematicians, 2018].

Publication Details

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ArXiv.org
Published
2025-04-01
Primary Topic
Geometric and Algebraic Topology
Type
article
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The Poisson boundary of Thompson's group $T$ is not the circle

ArXiv.org
Geometric and Algebraic Topology
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The Poisson boundary of Thompson's group $T$ is not the circle

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Abstract

Let $\mu$ be a nondegenerate probability measure with finite entropy on a countable group $G \leq \mathrm{Homeo}_+(S^1)$ of orientation-preserving homeomorphisms of the circle acting proximally, minimally and topologically nonfreely on $S^1$. We prove that the circle $S^1$ endowed with its unique $\mu$-stationary probability measure is not the Poisson boundary of $(G,\mu)$. When $G$ is Thompson's group $T$ and $\mu$ is finitely supported, this answers a question posed by B. Deroin [Ergodic Theory Dynam. Systems, 2013] and A. Navas [Proceedings of the International Congress of Mathematicians, 2018].

ArXiv.org
Openalex Percentile: Top 44%
Geometric and Algebraic Topology
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The Poisson boundary of Thompson's group $T$ is not the circle · ArXiv.org (2025) | TGRS Research Map | TGRS