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We study an invariant of dynamical systems called naive entropy, which is defined for both measurable and topological actions of any countable group. We focus on nonamenable groups, in which case the invariant is two-valued, with every…

Dynamical Systems · Mathematics 2016-02-23 Peter Burton

In previous work, we defined extended versions of von Neumann dimension for Banach space representations of sofic groups. The main application was a definition of l^{p}-dimension and, using this, a proof that the actions of a countable…

Functional Analysis · Mathematics 2015-08-12 Ben Hayes

We continue the study of how one can define means of infinite sets. We introduce many new properties, investigate their relations to each other and how they can typify a mean. We collect the properties in property groups e.g. for…

Classical Analysis and ODEs · Mathematics 2018-09-27 Attila Losonczi

In this paper, we introduce a new entropy-like invariant, named Hausdorff metric entropy, for finitely generated semigroups acting on compact metric spaces from a set-valued view and study its properties. We establish the relation between…

Dynamical Systems · Mathematics 2016-01-14 Bingzhe Hou , Xu Wang

We introduce inner amenability for discrete p.m.p. groupoids and investigate its basic properties, examples, and the connection with central sequences in the full group of the groupoid or central sequences in the von Neumann algebra…

Operator Algebras · Mathematics 2020-05-27 Yoshikata Kida , Robin Tucker-Drob

We define a way of approximating actions on measure spaces using finite graphs; we then show that in quite general settings these graphs form a family of expanders if and only if the action is expanding in measure. This provides a somewhat…

Geometric Topology · Mathematics 2021-01-13 Federico Vigolo

In this paper we characterize spaces of $L^\infty$-functions on a compact Hausdorff space that are invariant under a transitive and continuous group action. This work generalizes the author's 2021 results concerning the specific case of…

Functional Analysis · Mathematics 2022-06-06 Samuel A. Hokamp

We consider random walks on finitely or countably generated free semigroups, and identify their Poisson boundaries for classes of measures which fail to meet the classical entropy criteria. In particular, we introduce the notion of…

Dynamical Systems · Mathematics 2019-08-13 Behrang Forghani , Giulio Tiozzo

Let $f: M\rightarrow M$ be a continuous map on a compact metric space $M$ equipped with a fixed metric $d$, and let $\tau$ be the topology on $M$ induced by $d$. First, we will establish some fundamental properties of the mean Hausdorff…

Dynamical Systems · Mathematics 2024-07-12 Jeovanny Muentes Acevedo , Alex Jenaro Becker , Alexandre Tavares Baraviera , Érick Scopel

Ergodic theory includes several notions of entropy for probability-preserving actions of countable groups. These include Kolmogorov--Sinai entropy based on F\o lner sequences for amenable groups, entropy defined using a random ordering of…

Operator Algebras · Mathematics 2026-03-23 Tim Austin

This is the first part in a series in which sofic entropy theory is generalized to class-bijective extensions of sofic groupoids. Here we define topological and measure entropy and prove invariance. We also establish the variational…

Dynamical Systems · Mathematics 2013-03-19 Lewis Bowen

We bound the nuclear dimension of crossed products associated to some partial actions of finite groups or $\mathbb{Z}$ on finite dimensional locally compact Hausdorff second countable spaces. Our results apply to globalizable partial…

Operator Algebras · Mathematics 2022-01-19 Shirly Geffen

We show that the asymptotic dimension of box spaces behaves (sub)additively with respect to extensions of groups. As a result, we obtain that for an elementary amenable group, the asymptotic dimension of any of its box spaces is bounded…

Metric Geometry · Mathematics 2015-08-21 Martin Finn-Sell , Jianchao Wu

We prove that the entropy map for countable Markov shifts of finite entropy is upper semi-continuous at ergodic measures. Note that the phase space is non-compact. Applications to systems that can be coded by these shifts, such as positive…

Dynamical Systems · Mathematics 2021-08-16 Godofredo Iommi , Mike Todd , Aníbal Velozo

Let $f:X\to X$ be a dominating meromorphic map of a compact K\"ahler surface of large topological degree. Let $S$ be a positive closed current on $X$ of bidegree $(1,1)$. We consider an ergodic measure $\nu$ of large entropy supported by…

Dynamical Systems · Mathematics 2014-02-17 Henry de Thelin , Gabriel Vigny

We study topological realizations of countable Borel equivalence relations, including realizations by continuous actions of countable groups, with additional desirable properties. Some examples include minimal realizations on any perfect…

Logic · Mathematics 2025-08-07 Joshua Frisch , Alexander Kechris , Forte Shinko , Zoltán Vidnyánszky

We define a hierarchy of systems with topological completely positive entropy in the context of continuous countable amenable group actions on compact metric spaces. For each countable ordinal we construct a dynamical system on the…

Dynamical Systems · Mathematics 2021-08-30 Sebastián Barbieri , Felipe García-Ramos

We show that for any countable amenable group action, along F{\o}lner sequences that have for any $c>1$ a two sided $c$-tempered tail, one have universal estimate for the probability that there are $n$ fluctuations in the ergodic averages…

Dynamical Systems · Mathematics 2019-02-22 Uri Gabor

We study actions of countable discrete groups which are amenable in the sense that there exists a mean on X which is invariant under the action of G. Assuming that G is nonamenable, we obtain structural results for the stabilizer subgroups…

Group Theory · Mathematics 2020-12-16 Robin Tucker-Drob

In this paper, we introduce and investigate the notions of Mean Dimension and Metric Mean Dimension for generalized iterated function systems (IFS). We establish basic properties of these invariants and prove that Mean Dimension is always…

Dynamical Systems · Mathematics 2026-04-15 Welington Cordeiro , Maria José Pacifico , Xuan Zhang