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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 explore classifiability of crossed products of actions of countable amenable groups on compact, metrizable spaces. It is completely understood when such crossed products are simple, separable, unital, nuclear and satisfy the UCT: these…

Operator Algebras · Mathematics 2024-05-08 Eusebio Gardella , Shirly Geffen , Rafaela Gesing , Grigoris Kopsacheilis , Petr Naryshkin

We study smooth actions by lattices in higher-rank simple Lie groups. Assuming one element of the action acts with positive topological entropy, we prove a number of new rigidity results. For lattices in $\mathrm{SL}(n,\mathbb{R})$ acting…

Dynamical Systems · Mathematics 2025-01-24 Aaron Brown , Homin Lee

We introduce a notion of entropy for automorphisms of discrete groups which admit amenable actions on a compact space. This entropy is dual to classical topological entropy in the sense that if G is discrete and abelian then our notion of…

Operator Algebras · Mathematics 2007-05-23 N. P. Brown , E. Germain

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

It is shown that every accessible group which is integrable orbit equivalent to a free group is virtually free. Moreover, we also show that any integrable orbit-equivalence between finitely generated groups extends to their end…

Dynamical Systems · Mathematics 2016-01-05 Lewis Bowen

We show that any free product of two countable groups, one of them being infinite, admits a faithful and homogeneous action on the Random Graph. We also show that a large class of HNN extensions or free products, amalgamated over a finite…

Group Theory · Mathematics 2021-05-26 Pierre Fima , Soyoung Moon , Yves Stalder

In this short note we construct two countable, infinite conjugacy class groups which admit free, ergodic, probability measure preserving orbit equivalent actions, but whose group von Neumann algebras are not (stably) isomorphic.

Operator Algebras · Mathematics 2018-02-27 Ionut Chifan , Adrian Ioana

In this note a notion of generalized topological entropy for arbitrary subsets of the space of all sequences in a compact topological space is introduced. It is shown that for a continuous map on a compact space the generalized topological…

Dynamical Systems · Mathematics 2024-10-29 Maysam Maysami Sadr , Mina Shahrestani

In this paper, we show that if a group acts isometrically on a good hyperbolic space of finite volume entropy through a non-elementary action, then it admits an affine action on some $L^p$ -space with an unbounded orbit for sufficiently…

Group Theory · Mathematics 2025-08-19 Yanlong Hao

The purpose of this note is twofold. In the first part we observe that two finitely generated non-amenable groups are quasi-isometric if and only if they admit topologically orbit equivalent Cantor minimal actions. In particular, free…

Dynamical Systems · Mathematics 2017-06-21 Kostya Medynets , Roman Sauer , Andreas Thom

The notion of entropy appears in many fields and this paper is a survey about entropies in several branches of Mathematics. We are mainly concerned with the topological and the algebraic entropy in the context of continuous endomorphisms of…

General Topology · Mathematics 2013-08-20 Dikran Dikranjan , Anna Giordano Bruno

We show that for a finitely generated group of $C^2$ circle diffeomorphisms, the entropy of the action equals the entropy of the restriction of the action to the non-wandering set.

Dynamical Systems · Mathematics 2009-01-29 Eduardo Jorquera

We continue our study of the outer Pinsker factor for probability measure-preserving actions of sofic groups. Using the notion of doubly quenched convergence developed by Austin, we prove that in many cases the outer Pinsker factor of a…

Dynamical Systems · Mathematics 2021-03-26 Ben Hayes

We introduce the class of strongly sofic monoids. This class of monoids strictly contains the class of sofic groups and is a proper subclass of the class of sofic monoids. We define and investigate sofic topological entropy for actions of…

Group Theory · Mathematics 2025-02-10 Tullio Ceccherini-Silberstein , Michel Coornaert , Xuan Kien Phung

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 this note we study some properties of topological entropy for non-compact non-metrizable spaces. We prove that if a uniformly continuous self-map $f$ of a uniform space has topological shadowing property then the map $f$ has positive…

Dynamical Systems · Mathematics 2016-11-30 Seyyed Alireza Ahmadi

To an ergodic, essentially free and measure-preserving action of a non-amenable Baumslag-Solitar group on a standard probability space, a flow is associated. The isomorphism class of the flow is shown to be an invariant of such actions of…

Group Theory · Mathematics 2015-01-05 Yoshikata Kida

Consider a countable amenable group acting by homeomorphisms on a compact metrizable space. Chung and Li asked if expansiveness and positive entropy of the action imply existence of an off-diagonal asymptotic pair. For algebraic actions of…

Dynamical Systems · Mathematics 2019-08-15 Tom Meyerovitch

We show that every free continuous action of a countably infinite elementary amenable group on a finite-dimensional compact metrizable space is almost finite. As a consequence, the crossed products of minimal such actions are…

Dynamical Systems · Mathematics 2026-04-22 David Kerr , Petr Naryshkin