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We characterise the groupoid $C^*$-algebras associated to the transformation groupoids of injective actions of discrete countable Ore semi-groups on compact topological spaces in terms of the reduced crossed product from the dual actions,…

Operator Algebras · Mathematics 2024-04-23 Xiangqi Qiang , Chengjun Hou

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 obtain some general restrictions on the continuous endomorphisms of a profinite group G under the assumption that G has only finitely many open subgroups of each index (an assumption which automatically holds, for instance, if G is…

Group Theory · Mathematics 2011-12-19 Colin D. Reid

We give conditions for when continuous orbit equivalence of one-sided shift spaces implies flow equivalence of the associated two-sided shift spaces. Using groupoid techniques, we prove that this is always the case for shifts of finite…

Dynamical Systems · Mathematics 2018-10-08 Toke Meier Carlsen , Søren Eilers , Eduard Ortega , Gunnar Restorff

We study equivalence relations $\mathcal R(\Gamma\curvearrowright G)$ that arise from left translation actions of countable groups on their profinite completions. Under the assumption that the action $\Gamma\curvearrowright G$ is free and…

Dynamical Systems · Mathematics 2015-08-03 Adrian Ioana

We study the classification of group actions on C*-algebras up to equivariant KK-equivalence. We show that any group action is equivariantly KK-equivalent to an action on a simple, purely infinite C*-algebra. We show that a conjecture of…

K-Theory and Homology · Mathematics 2021-08-25 Ralf Meyer

We define an infinite graded graph of ordered pairs and a~canonical action of the group $\mathbb{Z}$ (the adic action) and of the infinite sum of groups of order two~$\mathcal{D}=\sum_1^{\infty} \mathbb{Z}/2\mathbb{Z}$ on the path space of…

Dynamical Systems · Mathematics 2017-10-11 A. M. Vershik , P. B. Zatitskii

We show that for every countable group, any sequence of approximate homomorphisms with values in permutations can be realized as the restriction of a sofic approximation of an orbit equivalence relation. Moreover, this orbit equivalence…

Group Theory · Mathematics 2024-11-20 Ben Hayes , Srivatsav Kunnawalkam Elayavalli

We show an equivariant Kirchberg-Phillips-type absorption theorem for pointwise outer actions of discrete amenable groups on Kirchberg algebras with respect to natural model actions on the Cuntz algebras $\mathcal{O}_\infty$ and…

Operator Algebras · Mathematics 2018-10-04 Gabor Szabo

In this paper, we construct, for a certain class of semigroup dynamical systems, two operator algebras that are universal with respect to their corresponding covariance conditions: one being self-adjoint, and another being non-self-adjoint.…

Operator Algebras · Mathematics 2020-07-10 Boyu Li

Let V be a simple vertex operator algebra and G a finite automorphism group. Then there is a natural right G-action on the set of all inequivalent irreducible V-modules. Let S be a finite set of inequivalent irreducible V-modules which is…

Quantum Algebra · Mathematics 2007-05-23 C. Dong , G. Yamskulna

We establish orbit equivalence rigidity for any ergodic, essentially free and measure-preserving action on a standard Borel space with a finite positive measure of the mapping class group for a compact orientable surface with higher…

Group Theory · Mathematics 2015-02-02 Yoshikata Kida

We associate to every action of a Polish group on a standard probability space a Polish group that we call the orbit full group. For discrete groups, we recover the well-known full groups of pmp equivalence relations equipped with the…

Group Theory · Mathematics 2014-11-24 Alessandro Carderi , François Le Maître

Different versions for defining Ashtekar's generalized connections are investigated depending on the chosen smoothness category for the paths and graphs -- the label set for the projective limit. Our definition covers the analytic case as…

Mathematical Physics · Physics 2007-05-23 Christian Fleischhack

We give an elementary proof for Lewis Bowen's theorem saying that two Bernoulli actions of two free groups, each having arbitrary base probability spaces, are stably orbit equivalent. Our methods also show that for all compact groups K and…

Operator Algebras · Mathematics 2013-10-03 Niels Meesschaert , Sven Raum , Stefaan Vaes

In this work, we introduce the type and typeset invariants for equicontinuous group actions on Cantor sets; that is, for generalized odometers. These invariants are collections of equivalence classes of asymptotic Steinitz numbers…

Dynamical Systems · Mathematics 2024-10-17 Steven Hurder , Olga Lukina

We establish conditions under which the universal and reduced norms coincide for a Fell bundle over a groupoid. Specifically, we prove that the full and reduced C*-algebras of any Fell bundle over a measurewise amenable groupoid coincide,…

Operator Algebras · Mathematics 2012-01-05 Aidan Sims , Dana P. Williams

We present a simple approach to questions of topological orbit equivalence for actions of countable groups on topological and smooth manifolds. For example, for any action of a countable group $\Gamma$ on a topological manifold where the…

Dynamical Systems · Mathematics 2007-05-23 David Fisher , Kevin Whyte

Given an ergodic probability measure preserving dynamical system $\G\acts (X,\mu)$, where $\G$ is a finitely generated countable group, we show that the asymptotic growth of the number of finite models for the dynamics, in the sense of…

Dynamical Systems · Mathematics 2011-12-21 Ken Dykema , David Kerr , Mikael Pichot

We give a sufficient condition for isometric actions to have the congruency of orbits, that is, all orbits are isometrically congruent to each other. As applications, we give simple and unified proofs for some known congruence results, and…

Differential Geometry · Mathematics 2012-12-18 Akira Kubo , Hiroshi Tamaru