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We define equivariant projective unitary stable bundles as the appropriate twists when defining K-theory as sections of bundles with fibers the space of Fredholm operators over a Hilbert space. We construct universal equivariant projective…

Algebraic Topology · Mathematics 2018-05-16 Noe Barcenas , Jesus Espinoza , Michael Joachim , Bernardo Uribe

By combining R{\o}rdam's construction and the author's previous construction, we provide the first examples of amenable actions of non-amenable groups on simple separable nuclear C*-algebras that are neither stably finite nor purely…

Operator Algebras · Mathematics 2025-03-03 Yuhei Suzuki

Given a graded ample Hausdorff groupoid, we realise its graded Steinberg algebra as a partial skew inverse semigroup ring. We use this to show that for a partial action of a discrete group on a locally compact Hausdorff topological space,…

Rings and Algebras · Mathematics 2017-08-18 Roozbeh Hazrat , Huanhuan Li

An action of a compact, in particular finite group on a C*-algebra is called properly outer if no automorphism of the group that is distinct from identity is implemented by a unitary element of the algebra of local multipliers of the…

Operator Algebras · Mathematics 2024-12-03 Costel Peligrad

We classify a large class of Z^2-actions on the Kirchberg algebras employing the Kasparov group KK^1 as the space of classification invariants.

Operator Algebras · Mathematics 2009-12-19 Masaki Izumi , Hiroki Matui

Let G be a discrete group and let X be a G-finite, proper G-CW-complex. We prove that Kasparov's equivariant K-homology groups KK^G(C_0(X),\C) are isomorphic to the geometric equivariant K-homology groups of X that are obtained by making…

K-Theory and Homology · Mathematics 2012-10-12 Paul Baum , Nigel Higson , Thomas Schick

In this paper, we study the equivariant homotopy type of a connected sum of linear actions on complex projective planes defined by Hambleton and Tanase. These actions are constructed for cyclic groups of odd order. We construct cellular…

Algebraic Topology · Mathematics 2021-09-28 Samik Basu , Pinka Dey , Aparajita Karmakar

We consider a family of Cuntz-Pimsner algebras associated to self-similar group actions, and their Toeplitz analogues. Both families carry natural dynamics implemented by automorphic actions of the real line, and we investigate the…

Operator Algebras · Mathematics 2014-05-20 Marcelo Laca , Iain Raeburn , Jacqui Ramagge , Michael F. Whittaker

We introduce and compare two approaches to equivariant homotopy theory in a topological or ordinary Quillen model category. For the topological model category of spaces, we generalize Piacenza's result that the categories of topological…

Algebraic Topology · Mathematics 2017-03-06 Marc Stephan

A classification theorem is obtained for a class of unital simple separable amenable Z-stable C*-algebras which exhausts all possible values of the Elliott invariant for unital stably finite simple separable amenable Z-stable C*-algebras.…

Operator Algebras · Mathematics 2021-05-05 Guihua Gong , Huaxin Lin , Z. Niu

We prove a new weak mean ergodic theorem (Theorem A) for 1-cocycles associated to weakly mixing representations of amenable groups. Let $G$ be a finitely generated, discrete, amenable group $G$ which admits a controlled Folner sequence. We…

Group Theory · Mathematics 2012-08-06 Ionut Chifan , Thomas Sinclair

We characterize group compactifications of discrete groups for which there exists an equivariant retraction onto the boundary. In particular, we prove an equivariant analogue of Brouwer's No-Retraction theorem for large classes of group…

Group Theory · Mathematics 2025-09-15 Yair Hartman , Aranka Hrušková , Mehrdad Kalantar , Tomer Zimhoni

In this paper, we consider the Toeplitz algebra associated to actions of Ore semigroups on $C^{*}$-algebras. In particular, we consider injective and surjective actions of such semigroups. We use the theory of groupoid dynamical systems to…

Operator Algebras · Mathematics 2016-01-22 S. Sundar

The results of a previous paper on the equivariant homotopy theory of crossed complexes are generalised from the case of a discrete group to general topological groups. The principal new ingredient necessary for this is an analysis of…

Algebraic Topology · Mathematics 2016-08-15 R Brown , M Golasiński , T Porter , A Tonks

In this paper we study uniform quasiconformal groups of Carnot-by-Carnot groups. We show that they can be conjugated into conformal groups provided the induced action on the space of distinct pairs is cocompact. Following the approach of…

Group Theory · Mathematics 2024-03-07 Tullia Dymarz , David Fisher , Xiangdong Xie

We give a complete classification up to cocycle conjugacy of uniformly outer actions of Z^2 on UHF algebras. In particular, it is shown that any two uniformly outer actions of Z^2 on a UHF algebra of infinite type are cocycle conjugate. We…

Operator Algebras · Mathematics 2007-08-31 Takeshi Katsura , Hiroki Matui

Let A be a unital separable C*-algebra, and D a K_1-injective strongly self-absorbing C*-algebra. We show that if A is D-absorbing, then the crossed product of A by a compact second countable group or by Z or by R is D-absorbing as well,…

Operator Algebras · Mathematics 2007-05-23 Ilan Hirshberg , Wilhelm Winter

In this note we present an analogue of equivariant formality in $K$-theory and show that it is equivalent to equivariant formality \emph{\`a la} Goresky-Kottwitz-MacPherson. We also apply this analogue to give alternative proofs of…

Algebraic Topology · Mathematics 2019-02-13 Chi-Kwong Fok

For a proper, cocompact action by a locally compact group of the form $H \times G$, with $H$ compact, we define an $H \times G$-equivariant index of $H$-transversally elliptic operators, which takes values in $KK_*(C^*H, C^*G)$. This…

K-Theory and Homology · Mathematics 2020-06-24 Peter Hochs , Hang Wang

For a natural class of cohomology theories with support (including \'etale or pro-\'etale cohomology with suitable coefficients), we prove a moving lemma for cohomology classes with support on smooth quasi-projective k-varieties that admit…

Algebraic Geometry · Mathematics 2026-05-27 Stefan Schreieder