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We apply the One-Sided Action Theorem from the first paper in this series to prove that Rieffel's Morita equivalence between the reduced crossed product by a proper saturated action and the generalized fixed-point algebra is a quotient of a…

Operator Algebras · Mathematics 2012-11-30 S. Kaliszewski , Paul S. Muhly , John Quigg , Dana P. Williams

We define a semidirect product groupoid of a system of partially defined local homeomorphisms $T=(T_{1},..., T_{r})$. We prove that this construction gives rise to amenable groupoids. The associated algebra is a Cuntz-like algebra. We use…

Operator Algebras · Mathematics 2008-11-12 Ionel Popescu , Iulian Popescu

We construct a crossed product Banach algebra from a Banach algebra dynamical system $(A,G,\alpha)$ and a given uniformly bounded class $R$ of continuous covariant Banach space representations of that system. If $A$ has a bounded left…

Functional Analysis · Mathematics 2011-08-16 Sjoerd Dirksen , Marcel de Jeu , Marten Wortel

This paper develops a duality theory for connected cochain DG algebras, with particular emphasis on the non-commutative aspects. One of the main items is a dualizing DG module which induces a duality between the derived categories of DG…

Rings and Algebras · Mathematics 2010-12-20 Peter Jorgensen

Given a coaction $\delta$ of a locally compact group $G$ on a $\mathrm{C}^*$-algebra $A$, we study the relationship between two different forms of coaction invariance of ideals of $A$ and the ideals of the corresponding crossed product…

Operator Algebras · Mathematics 2026-01-13 Matthew Gillespie , Benjamin Jones , S. Kaliszewski , John Quigg

Using Poincar\'e duality in K-theory, we state and prove a Lefschetz fixed point formula for endomorphisms of cross product C*-algebras $C_0(X)\cross G$ coming from covariant pairs. Here $G$ is assumed countable, $X$ a manifold, and…

K-Theory and Homology · Mathematics 2008-05-29 Siegfried Echterhoff , Heath Emerson , Hyun Jeong Kim

Let $ G $ be a locally compact group. We study the categories of $ L^{\infty}(G) $-comodules and $ L(G) $-comodules in the setting of dual operator spaces and the associated crossed products. It is proved that every $ L^{\infty}(G)…

Operator Algebras · Mathematics 2020-04-16 Dimitrios Andreou

In order to simultaneously generalize matrix rings and group graded crossed products, we introduce category crossed products. For such algebras we describe the center and the commutant of the coefficient ring. We also investigate the…

Rings and Algebras · Mathematics 2008-12-09 Johan Öinert , Patrik Lundström

We analzye Rieffel's construction of generalized fixed point algebras in the setting of group actions on Hilbert modules. Let G be a locally compact group acting on a C*-algebra B. We construct a Hilbert module F over the reduced crossed…

Operator Algebras · Mathematics 2015-10-23 Ralf Meyer

The aim of this paper is to study a problem raised by N. C. Phillips concerning the existence of Takai duality for $L^p$ operator crossed products $F^{p}(G,A,\alpha)$, where $G$ is a locally compact Abelian group, $A$ is an $L^{p}$ operator…

Operator Algebras · Mathematics 2022-12-13 Zhen Wang , Sen Zhu

In his seminal paper "Generalized Fixed Point Algebras and Square-Integrable Group Actions", Ralf Meyer showed how to construct generalized fixed-point algebras for $ C^{\ast} $-dynamical systems via their square-integrable representations…

Representation Theory · Mathematics 2017-04-14 Leonard Huang

The purpose of this paper is to introduce a consistent notion of universal and reduced crossed products by actions and coactions of groups on operator systems and operator spaces. In particular we shall put emphasis to reveal the full power…

Operator Algebras · Mathematics 2019-10-16 Massoud Amini , Siegfried Echterhoff , Hamed Nikpey

Consider a coaction $\delta$ of a locally compact group $G$ on a \cstar algebra $A$, and a closed normal subgroup $N$ of $G$. We prove, following results of Echterhoff for abelian $G$, that Mansfield's imprimitivity between…

funct-an · Mathematics 2008-02-03 S. Kaliszewski , John Quigg , Iain Raeburn

We develop a relative boundary theory for actions of discrete groups on compact spaces and use it to derive rigidity results for reduced crossed products. For a discrete group $\Gamma$ acting on a compact space $X$ and a subgroup $H$, we…

Operator Algebras · Mathematics 2026-01-08 Tattwamasi Amrutam , Chunlin Liu

Let $(\mathcal G, \Sigma)$ be an ordered abelian group with Haar measure $\mu$, let $(\mathcal A, \mathcal G, \alpha)$ be a dynamical system and let $\mathcal A\rtimes_{\alpha} \Sigma $ be the associated semicrossed product. Using Takai…

Operator Algebras · Mathematics 2017-10-20 Elias Katsoulis , Christopher Ramsey

In further study of the application of crossed-product functors to the Baum-Connes Conjecture, Buss, Echterhoff, and Willett introduced various other properties that crossed-product functors may have. Here we introduce and study analogues…

Operator Algebras · Mathematics 2018-03-16 S. Kaliszewski , Magnus B. Landstad , John Quigg

Given an infinite, compact, monothetic group $G$ we study decompositions and structure of unbounded derivations in a crossed product C$^*$-algebra $C(G)\rtimes\Z$ obtained from a translation on $G$ by a generator of a dense cyclic subgroup.…

Operator Algebras · Mathematics 2023-06-22 Slawomir Klimek , Matt McBride

Given a labeling c of the edges of a directed graph E by elements of a discrete group G, one can form a skew-product graph E cross_c G. We show, using the universal properties of the various constructions involved, that there is a coaction…

Operator Algebras · Mathematics 2007-05-23 S. Kaliszewski , John Quigg , Iain Raeburn

We study crossed products of arbitrary operator algebras by locally compact groups of completely isometric automorphisms. We develop an abstract theory that allows for generalizations of many of the fundamental results from the selfadjoint…

Operator Algebras · Mathematics 2018-11-21 Elias Katsoulis , Christopher Ramsey

Let P be a semigroup that admits an embedding into a group G. Assume that the embedding satisfies a certain Toeplitz condition and that the Baum-Connes conjecture holds for G. We prove a formula describing the K- theory of the reduced…

Operator Algebras · Mathematics 2012-05-25 Joachim Cuntz , Siegfried Echterhoff , Xin Li