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We investigate the representation theory of the crossed-product C*-algebra associated to a compact group G acting on a locally compact space X when the stability subgroups vary discontinuously. Our main result applies when G has a principal…

Operator Algebras · Mathematics 2015-08-27 Robert Archbold , Astrid an Huef

We consider a twisted action of a discrete group G on a unital C*-algebra A and give conditions ensuring that there is a bijective correspondence between the maximal invariant ideals of A and the maximal ideals in the associated reduced…

Operator Algebras · Mathematics 2023-07-19 Erik Bédos , Roberto Conti

Generalizing the case of the Toeplitz algebra by Brake and Winter, we prove that the nuclear dimension of a C*-algebra extension of C(X) by the compact operators is equal to the dimension of X.

Operator Algebras · Mathematics 2023-09-28 Ruaridh Gardner , Aaron Tikuisis

The multiplicative group of a number field acts by multiplication on the full adele ring of the field. Generalising a theorem of Laca and Raeburn, we explicitly describe the primitive ideal space of the crossed product C*-algebra associated…

Operator Algebras · Mathematics 2025-01-23 Chris Bruce , Takuya Takeishi

Given an action by a finite quantum group $\mathbb{G}$ on a von Neumann algebra $M$, we prove that a number of familiar $W^*$ properties are equivalent for $M$ and the fixed-point algebra $M^{\mathbb{G}}$ (i.e. hold or not simultaneously…

Operator Algebras · Mathematics 2025-04-22 Alexandru Chirvasitu

We compute the nuclear dimension of extensions of C*-algebras involving commutative unital quotients and stable Kirchberg ideals. We identify the finite directed graphs whose C*-algebras are covered by this theorem.

Operator Algebras · Mathematics 2025-05-13 Samuel Evington , Abraham C. S. Ng , Aidan Sims , Stuart White

We study a tracial notion of Z-absorption for simple, unital C*-algebras. We show that if A is a C*-algebra for which this property holds then A has almost unperforated Cuntz semigroup, and if in addition A is nuclear and separable we show…

Operator Algebras · Mathematics 2013-05-02 Ilan Hirshberg , Joav Orovitz

We study the ideal structure of $C^*$-algebras arising from $C^*$-correspondences. We prove that gauge-invariant ideals of our $C^*$-algebras are parameterized by certain pairs of ideals of original $C^*$-algebras. We show that our…

Operator Algebras · Mathematics 2007-05-23 Takeshi Katsura

We consider compact group actions on C*- and W*- algebras. We prove results that relate the duality property of the action (as defined in the Introduction) with other relevant properties of the system such as the relative commutant of the…

Operator Algebras · Mathematics 2020-10-13 Costel Peligrad

We take a new look at dilation theory for nonself-adjoint operator algebras. Among the extremal (co)extensions of a representation, there is a special property of being fully extremal. This allows a refinement of some of the classical…

Operator Algebras · Mathematics 2011-09-02 Kenneth R. Davidson , Elias G. Katsoulis

We consider the functor C that to a unital C*-algebra A assigns the partial order set C(A) of its commutative C*-subalgebras ordered by inclusion. We investigate how some C*-algebraic properties translate under the action of C to…

Operator Algebras · Mathematics 2016-10-07 Bert Lindenhovius

If $k$ is an infinite cardinal, we say a C*-algebra $\mathcal{A}$ is residually less than $k$ dimensional, $R_{<k}D,$ if the family of representations of $\mathcal{A}$ on Hilbert spaces of dimension less than $k$ separates the points of…

Operator Algebras · Mathematics 2011-08-02 Don Hadwin

Elliott dimension drop interval algebra is an important class among all $C^*$-algebras in the classification theory. Especially, they are building stones of $\mathcal{AHD}$ algebra and the latter contains all $AH$ algebras with the ideal…

Operator Algebras · Mathematics 2019-05-30 Chunlan Jiang , Liangqing Li , Kun Wang

Partial actions of discrete groups on $C^*$-algebras and the associated crossed products have been studied by Exel and McClanahan. We characterise these crossed products in terms of the spectral subspaces of the dual coaction, generalising…

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

We compute the K-theory for C*-algebras naturally associated with rings of integers in number fields. The main ingredient is a duality theorem for arbitrary global fields. It allows us to identify the crossed product arising from affine…

Operator Algebras · Mathematics 2009-06-29 Joachim Cuntz , Xin Li

We study the space of continuous $Z^d$-actions on the Cantor set, particularly questions on the existence and nature of actions whose isomorphism class is dense (Rohlin's property). Kechris and Rosendal showed that for $d=1$ there is an…

Dynamical Systems · Mathematics 2014-09-23 Michael Hochman

We show that C*-algebras generated by irreducible representations of finitely generated nilpotent groups satisfy the universal coefficient theorem of Rosenberg and Schochet. This result combines with previous work to show that these…

Operator Algebras · Mathematics 2023-07-19 Caleb Eckhardt , Elizabeth Gillaspy

To each integral domain R with finite quotients we associate a purely infinite simple C*-algebra in a very natural way. Its stabilization can be identified with the crossed product of the algebra of continuous functions on the "finite adele…

Operator Algebras · Mathematics 2008-07-10 Joachim Cuntz , Xin Li

We analyze the decomposition rank (a notion of covering dimension for nuclear $C^*$-algebras introduced by E. Kirchberg and the author) of subhomogeneous $C^*$-algebras. In particular we show that a subhomogeneous $C^*$-algebra has…

Operator Algebras · Mathematics 2007-05-23 Wilhelm Winter

We prove a noncommutative variant of Saskin's classical theorem -- on the connection between Choquet boundaries for function spaces and Korovkin sets -- for operator systems generating separable Type I C*-algebras. The main result implies…

Operator Algebras · Mathematics 2015-05-22 Craig Kleski