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We prove that the C*-algebra of a minimal diffeomorphism satisfies Blackadar's Fundamental Comparability Property for positive elements. This leads to the classification, in terms of K-theory and traces, of the isomorphism classes of…

Operator Algebras · Mathematics 2015-05-13 Andrew S. Toms

In the theory of C*-algebras, interesting noncommutative structures arise as deformations of the tensor product. For instance, the rotation algebra may be seen as a scalar twist deformation of the tensor product of the functions on the…

Operator Algebras · Mathematics 2013-03-04 Moritz Weber

We consider a locally compact Hausdorff groupoid $G$, and twist by a more general locally compact Hausdorff abelian group $\Gamma$ rather than the complex unit circle $\mathbb{T}$. We investigate the construction of $C^*$-algebras in…

Operator Algebras · Mathematics 2025-11-14 Lisa Orloff Clark , Michael Ó Ceallaigh , Hung Pham

This paper investigates the $\mathrm{K}$-theory of twisted groupoid $\mathrm{C}^*$-algebras. It is shown that a homotopy of twists on an ample groupoid satisfying the Baum-Connes conjecture with coefficients gives rise to an isomorphism…

Operator Algebras · Mathematics 2019-04-25 Christian Bönicke

Let $G$ be a compact quantum group. We show that given a $G$-equivariant $\mathrm{C}^*$-correspondence $E$, the Pimsner algebra $\mathcal{O}_E$ can be naturally made into a $G$-$\mathrm{C}^*$-algebra. We also provide sufficient conditions…

Operator Algebras · Mathematics 2024-01-30 Suvrajit Bhattacharjee , Soumalya Joardar

In this paper, we develop a quantitative K-theory for filtered C*-algebras. Particularly interesting examples of filtered C*-algebras include group C*-algebras, crossed product C*-algebras and Roe algebras. We prove a quantitative version…

Operator Algebras · Mathematics 2012-04-17 Hervé Oyono-Oyono , Guoliang Yu

In this paper, we introduce a new technique in the study of the $*$-regular closure of some specific group algebras $KG$ inside $\mathcal{U}(G)$, the $*$-algebra of unbounded operators affiliated to the group von Neumann algebra…

Rings and Algebras · Mathematics 2024-02-13 Pere Ara , Joan Claramunt

In this paper, we apply quantitative operator K-theory to develop an algorithm for computing K-theory for the class of filtered C *-algebras with asymptotic finite nuclear decomposition. As a consequence, we prove the K{\"u}nneth formula…

Operator Algebras · Mathematics 2016-09-14 Hervé Oyono-Oyono , Guoliang Yu

Given a normal subgroup bundle $\mathcal A$ of the isotropy bundle of a groupoid $\Sigma$, we obtain a twisted action of the quotient groupoid $\Sigma/\mathcal A$ on the bundle of group $C^*$-algebras determined by $\mathcal A$ whose…

Operator Algebras · Mathematics 2020-11-24 Marius Ionescu , Alex Kumjian , Jean N. Renault , Aidan Sims , Dana P. Williams

We compute the equivariant $K$-theory $K_G^*(G)$ for a simply connected Lie group $G$ (acting on itself by conjugation). We prove that $K_G^*(G)$ is isomorphic to the algebra of Grothendieck differentials on the representation ring. We also…

dg-ga · Mathematics 2007-05-23 Jean-Luc Brylinski , Bin Zhang

We study the $C^*$-algebras arising in the construction of Guionnet-Jones-Shlyakhtenko (GJS) for a planar algebra. In particular, we show they are pairwise strongly Morita equivalent, we compute their $K$-groups, and we prove many…

Operator Algebras · Mathematics 2014-01-14 Michael Hartglass , David Penneys

We establish conditions under which an inclusion of finitely aligned left-cancellative small categories induces inclusions of twisted C*-algebras. We also present an example of an inclusion of finitely aligned left-cancellative monoids that…

Operator Algebras · Mathematics 2025-06-24 Alexander Mundey , Aidan Sims

Motivated by the Farrell-Jones Conjecture for group rings, we formulate the $\mathcal{C}$op-Farrell-Jones Conjecture for the K-theory of Hecke algebras of td-groups. We prove this conjecture for (closed subgroups of) reductive p-adic groups…

K-Theory and Homology · Mathematics 2023-12-22 Arthur Bartels , Wolfgang Lueck

We provide a complete classification of the class of unital graph $C^*$-algebras - prominently containing the full family of Cuntz-Krieger algebras - showing that Morita equivalence in this case is determined by ordered, filtered…

Operator Algebras · Mathematics 2021-09-20 Søren Eilers , Gunnar Restorff , Efren Ruiz , Adam P. W. Sørensen

Let $C^*$-algebra that is acted upon by a compact abelian group. We show that if the fixed-point algebra of the action contains a Cartan subalgebra $D$ satisfying an appropriate regularity condition, then $A$ is the reduced $C^*$-algebra of…

Operator Algebras · Mathematics 2019-09-12 Jonathan Brown , Adam Fuller , David Pitts , Sarah Reznikoff

We provide a new computation of the K-theory of the group $C^*$-algebra of the solvable Baumslag-Solitar group $BS(1,n)\;(n\neq 1)$; our computation is based on the Pimsner-Voiculescu 6-terms exact sequence, by viewing $BS(1,n)$ as a…

Operator Algebras · Mathematics 2016-04-20 Sanaz Pooya , Alain Valette

The notion of qausi-product actions of a compact group on a C$^*$-algebra was introduced by Bratteli et al. in their attempt to seek an equivariant analogue of Glimm's characterization of non-type I C$^*$-algebras. We show that a faithful…

Operator Algebras · Mathematics 2024-05-07 Masaki Izumi

Let Gamma be a semidirect product of the form Z^n rtimes Z/p where p is prime and the Z/p-action on Z^n is free away from the origin. We will compute the topological K-theory of the real and complex group C*-algebra of Gamma and show that…

K-Theory and Homology · Mathematics 2015-11-30 James F. Davis , Wolfgang Lueck

Let $\gamma = (\gamma_1,...,\gamma_N)$, $N \geq 2$, be a system of proper contractions on a complete metric space. Then there exists a unique self-similar non-empty compact subset $K$. We consider the union ${\mathcal G} = \cup_{i=1}^N…

Operator Algebras · Mathematics 2007-05-23 Tsuyoshi Kajiwara , Yasuo Watatani

Let H(R,q) be an affine Hecke algebra with a positive parameter function q. We are interested in the topological K-theory of H(R,q), that is, the K-theory of its C*-completion C*_r (R,q). We will prove that $K_* (C*_r (R,q))$ does not…

K-Theory and Homology · Mathematics 2018-07-25 Maarten Solleveld