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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

We study amenable minimal Cantor systems of free groups arising from the diagonal actions of the boundary actions and certain Cantor systems. It is shown that every virtually free group admits continuously many amenable minimal Cantor…

Operator Algebras · Mathematics 2017-01-04 Yuhei Suzuki

Supramenability of groups is characterised in terms of invariant measures on locally compact spaces. This opens the door to constructing interesting crossed product C*-algebras for non-supramenable groups. In particular, stable Kirchberg…

Operator Algebras · Mathematics 2013-12-09 Julian Kellerhals , Nicolas Monod , Mikael Rordam

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 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

We introduce a wide class of countable groups, called properly proximal, which contains all non-amenable bi-exact groups, all non-elementary convergence groups, and all lattices in non-compact semi-simple Lie groups, but excludes all inner…

Operator Algebras · Mathematics 2018-11-15 Rémi Boutonnet , Adrian Ioana , Jesse Peterson

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

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 provide a detailed study of actions of the integers on compact quantum metric spaces, which includes general criteria ensuring that the associated crossed product algebra is again a compact quantum metric space in a natural way. We…

Operator Algebras · Mathematics 2021-07-01 Jens Kaad , David Kyed

When a locally compact group acts on a C*-correspondence, it also acts on the associated Cuntz-Pimsner algebra in a natural way. Hao and Ng have shown that when the group is amenable the Cuntz-Pimsner algebra of the crossed product…

Operator Algebras · Mathematics 2015-01-21 Erik Bédos , S. Kaliszewski , John Quigg , David Robertson

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

Amenable actions of locally compact groups on von Neumann algebras are investigated by exploiting the natural module structure of the crossed product over the Fourier algebra of the acting group. The resulting characterisation of…

Operator Algebras · Mathematics 2021-01-20 Andrew McKee , Reyhaneh Pourshahami

We examine crossed product C*-algebras associated with non-minimal free actions of countably infinite discrete abelian groups on the circle, extending the work of Putnam, Schmidt, and Skau. We obtain a large class of unital separable…

Operator Algebras · Mathematics 2026-04-21 Jamie Bell

We introduce the concept of crossed product of a product system by a locally compact group. We prove that the crossed product of a row-finite and faithful product system by an amenable group is also a row-finite and faithful product system.…

Operator Algebras · Mathematics 2022-12-23 Valentin Deaconu , Leonard Huang

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 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

By employing the external Kasparov product, Hawkins, Skalski, White and Zacharias constructed spectral triples on crossed product C$^\ast$-algebras by equicontinuous actions of discrete groups. They further raised the question for whether…

Operator Algebras · Mathematics 2026-01-28 Mario Klisse

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

In a recent paper, Pardo and the first named author introduced a class of C*-algebras which which are constructed from an action of a group on a graph. This class was shown to include many C*-algebras of interest, including all Kirchberg…

Operator Algebras · Mathematics 2014-06-30 Ruy Exel , Charles Starling

We prove the first rigidity and classification theorems for crossed product von Neumann algebras given by actions of non-discrete, locally compact groups. We prove that for arbitrary free probability measure preserving actions of connected…

Operator Algebras · Mathematics 2018-07-20 Arnaud Brothier , Tobe Deprez , Stefaan Vaes
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