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We show that all amenable, minimal actions of a large class of nonamenable countable groups on compact metric spaces have dynamical comparison. This class includes all nonamenable hyperbolic groups, many HNN-extensions, nonamenable…

Operator Algebras · Mathematics 2023-03-01 Eusebio Gardella , Shirly Geffen , Julian Kranz , Petr Naryshkin

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

We show that Cantor minimal $\mathbb{Z}\rtimes\mathbb{Z}_2$-systems and essentially free amenable odometers are almost finite. We also compute the homology groups of Cantor minimal $\mathbb{Z}\rtimes\mathbb{Z}_2$-systems and show that the…

Operator Algebras · Mathematics 2021-03-23 Eduard Ortega , Eduardo Scarparo

Let $G$ be a second-countable, locally compact group. In this article we study amenable $G$-actions on Kirchberg algebras that admit an approximately central embedding of a canonical quasi-free action on the Cuntz algebra…

Operator Algebras · Mathematics 2023-08-17 James Gabe , Gábor Szabó

We introduce the property of having good subgroups for actions of countable discrete groups on compact metrizable spaces, and show that it implies comparison when the acting group is amenable. As a consequence, free actions on…

Dynamical Systems · Mathematics 2025-01-20 Petr Naryshkin , Spyridon Petrakos

We construct an uncountable family of transversely Cantor laminations of compact spaces defined by free minimal actions of solvable groups, which are not affable and whose orbits are not quasi-isometric to Cayley graphs.

Dynamical Systems · Mathematics 2020-09-18 Fernando Alcalde Cuesta , Álvaro Lozano Rojo , Matilde Martínez

Grigorchuk and Medynets recently announced that the topological full group of a minimal Cantor Z-action is amenable. They asked whether the statement holds for all minimal Cantor actions of general amenable groups as well. We answer in the…

Dynamical Systems · Mathematics 2013-09-26 Gabor Elek , Nicolas Monod

It was shown by Rordam and the second named author that a countable group G admits an action on a compact space such that the crossed product is a Kirchberg algebra if, and only if, G is exact and non-amenable. This construction allows a…

Operator Algebras · Mathematics 2011-11-01 G. A. Elliott , A. Sierakowski

In this paper we consider the question of what abelian groups can arise as the $K$-theory of $\mathrm{C}^*$-algebras arising from minimal dynamical systems. We completely characterize the $K$-theory of the crossed product of a space $X$…

Operator Algebras · Mathematics 2020-12-22 Robin J. Deeley , Ian F. Putnam , Karen R. Strung

I combine recent results in the structure theory of nuclear C*-algebras and in topological dynamics to classify certain types of crossed products in terms of their Elliott invariants. In particular, transformation group C*-algebras…

Operator Algebras · Mathematics 2015-04-08 Wilhelm Winter

We study conditions that will ensure that a crossed product of a C*-algebra by a discrete exact group is purely infinite (simple or non-simple). We are particularly interested in the case of a discrete non-amenable exact group acting on a…

Operator Algebras · Mathematics 2010-11-22 Mikael Rordam , Adam Sierakowski

The basic notions and results of equivariant KK-theory concerning crossed products can be extended to the case of locally compact quantum groups. We recall these constructions and prove some usefull properties of subgroups and amalgamated…

Operator Algebras · Mathematics 2020-06-04 Roland Vergnioux

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 show that amenability of a group acting by homeomorphisms can be deduced from a certain local property of the action and recurrency of the orbital Schreier graphs. This covers amenability of a wide class groups, the amenability of which…

Group Theory · Mathematics 2017-10-05 Kate Juschenko , Volodymyr Nekrashevych , Mikael de la Salle

We prove that a crossed product algebra arising from a minimal dynamical system on the product of the Cantor set and the circle has real rank zero if and only if that system is rigid. In the case that cocycles take values in the rotation…

Operator Algebras · Mathematics 2016-09-07 Huaxin Lin , Hiroki Matui

Almost finiteness was introduced in the seminal work of Kerr as an dynamical analogue of Z-stability in the Toms-Winter conjecture. In this article, we provide the first examples of minimal, topologically free actions of amenable groups…

Dynamical Systems · Mathematics 2023-11-07 Matthieu Joseph

We study index pairings for crossed-product $C^*$-algebras arising from minimal actions on the Cantor set. We utilize Putnam's orbit-breaking AF-subalgebras and embeddings to show we can compute any index pairing for Cantor minimal system…

Operator Algebras · Mathematics 2025-06-02 Levi Lorenzo

We introduce the notion of tracial amenability for actions of discrete groups on unital, tracial C$^*$-algebras, as a weakening of amenability where all the relevant approximations are done in the uniform trace norm. We characterize tracial…

Operator Algebras · Mathematics 2024-02-26 Eusebio Gardella , Shirly Geffen , Julian Kranz , Petr Naryshkin , Andrea Vaccaro

We prove that any countable non-amenable group G admits a free minimal amenable purely infinite action on the non-compact Cantor set. This answers a question of Kellerhals, Monod and R{\o}rdam.

Dynamical Systems · Mathematics 2018-09-05 Gabor Elek

We introduce the notion of Zimmer amenability for actions of discrete quantum groups on von Neumann algebras. We prove generalizations of several fundamental results of the theory in the noncommutative case. In particular, we give a…

Operator Algebras · Mathematics 2018-03-20 Mohammad S. M. Moakhar
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