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We generalise recent results about quasi-Cartan, Cartan and diagonal subalgebras by introducing graded versions. We show that there is a correspondence between graded algebraic quasi-Cartan/ Cartan/ diagonal pairs and certain graded twisted…

Rings and Algebras · Mathematics 2025-06-02 Lisa Orloff Clark , Lynnel D. Naingue , Jocelyn P. Vilela

We observe almost divisibility for the original Cuntz semigroup of a simple AH algebra with strict comparison. As a consequence, the properties of strict comparison, finite nuclear dimension, and Z-stability are equivalent for such…

Operator Algebras · Mathematics 2011-02-07 Andrew S. Toms

We compute Picard groups of several nuclear and non-nuclear simple stably projectionless C*-algebras. In particular, the Picard group of Razak-Jacelon algebra W_2 is isomorphic to a semidirect product of Out(W_2) with R_+^\times. Moreover,…

Operator Algebras · Mathematics 2014-02-26 Norio Nawata

We associate cube complexes called completions to each subgroup of a right-angled Coxeter group (RACG). A completion characterizes many properties of the subgroup such as whether it is quasiconvex, normal, finite-index or torsion-free. We…

Geometric Topology · Mathematics 2021-04-14 Pallavi Dani , Ivan Levcovitz

We give a detailed introduction to the theory of Cuntz semigroups for C*-algebras. Beginning with the most basic definitions and technical lemmas, we present several results of historical importance, such as Cuntz's theorem on the existence…

Operator Algebras · Mathematics 2022-12-14 Eusebio Gardella , Francesc Perera

We prove that Z-stable, simple, separable, nuclear, non-unital C*-algebras have nuclear dimension at most 1. This completes the equivalence between finite nuclear dimension and Z-stability for simple, separable, nuclear, non-elementary…

Operator Algebras · Mathematics 2020-11-18 Jorge Castillejos , Samuel Evington

Let $\mathcal A$ be a separable, unital, approximately divisible C$^*$-algebra. We show that $\mathcal A$ is generated by two self-adjoint elements and the topological free entropy dimension of any finite generating set of $\mathcal A$ is…

Operator Algebras · Mathematics 2008-04-21 Weihua Li , Junhao Shen

Elliott and Kucerovsky stated that a non-unital extension of separable $C^\ast$-algebras with a stable ideal, is nuclearly absorbing if and only if the extension is purely large. However, their proof was flawed. We give a counter example to…

Operator Algebras · Mathematics 2016-09-07 James Gabe

In this paper, we present an explicit construction of twisted traces for quantum Coulomb branches of conical theories. We develop an operator representation of the Coulomb branch algebra and use it to derive integral formulas for the…

Representation Theory · Mathematics 2025-10-24 Keke Zhang

It is shown that the coloured isomorphism class of a unital, simple, $\mathcal{Z}$-stable, separable amenable C$^*$-algebra satisfying the Universal Coefficient Theorem (UCT) is determined by its tracial simplex.

Operator Algebras · Mathematics 2022-04-14 Jeffrey Im , George A. Elliott

Let $A$ be an amenable separable \CA and $B$ be a non-unital but $\sigma$-unital simple \CA with continuous scale. We show that two essential extensions $\tau_1$ and $\tau_2$ of $A$ by $B$ are approximately unitarily equivalent if and only…

Operator Algebras · Mathematics 2007-05-23 Huaxin Lin

We establish the tracial stability of a certain class of graph products of C*-algebras. This result involves the development of the "pincushion class" of finite graphs. We then apply this result in two ways. The first application yields a…

Operator Algebras · Mathematics 2019-03-07 Scott Atkinson

We exhibit a countably infinite family of simple, separable, nuclear, and mutually non-isomorphic C*-algebras which agree on K-theory and traces. The algebras do not absorb the Jiang-Su algebra Z tensorially, answering a question of N. C.…

Operator Algebras · Mathematics 2007-08-22 Andrew S. Toms

In this note we address a question of Don Hadwin: "Which groups have strongly quasidiagonal C*-algebras?" In recent work we showed that all finitely generated virtually nilpotent groups have strongly quasidiagonal C*-algebras, while…

Operator Algebras · Mathematics 2015-06-04 Caleb Eckhardt

The categories of almost modules and almost algebras are introduced as a convenient setting for the development of Faltings' method of almost etale extensions. After some preliminaries of general "almost homological algebra" we construct…

Algebraic Geometry · Mathematics 2007-05-23 Ofer Gabber , Lorenzo Ramero

In this paper, we introduce some classes of generalized tracial approximation ${\rm C^*}$-algebras. Consider the class of unital ${\rm C^*}$-algebras which are tracially $\mathcal{Z}$-absorbing (or have tracial nuclear dimension at most…

Operator Algebras · Mathematics 2022-08-30 George A. Elliott , Qingzhai Fan , Xiaochun Fang

Nuclear C*-algebras enjoy a number of approximation properties, most famously the completely positive approximation property. This was recently sharpened to arrange for the incoming maps to be sums of order-zero maps. We show that, in…

Operator Algebras · Mathematics 2017-08-25 Nathanial P. Brown , José R. Carrión , Stuart White

We extend in this paper the characterisation of a separable nuclear \cst-algebra given by Kirchberg proving that given a unital separable continuous field of nuclear C*-algebras A over a compact metrizable space X, the C(X)-algebra A is…

Operator Algebras · Mathematics 2016-09-07 Etienne Blanchard

For every Hecke C*-algebra of right-angled, hyperbolic type, we construct a smooth subalgebra to which traces associated with arbitrary conjugacy classes in the associated Coxeter group extend. We calculate the pairing with K-theory of the…

Operator Algebras · Mathematics 2026-03-25 Piotr Nowak , Sanaz Pooya , Sven Raum , Adam Skalski

We investigate the notion of tracial $\mathcal Z$-stability beyond unital C*-algebras, and we prove that this notion is equivalent to $\mathcal Z$-stability in the class of separable simple nuclear C*-algebras.

Operator Algebras · Mathematics 2023-04-05 Jorge Castillejos , Kang Li , Gabor Szabo