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We analyze the sequence obtained by consecutive applications of the Cantor-Bendixson derivative for a noncommutative scattered $C^*$-algebra $\mathcal A$, using the ideal $\mathcal I^{At}(\mathcal A)$ generated by the minimal projections of…

Operator Algebras · Mathematics 2018-04-04 Saeed Ghasemi , Piotr Koszmider

Let F be a right Hilbert C*-module over a C*-algebra B, and suppose that F is equipped with a left action, by compact operators, of a second C*-algebra A. Tensor product with F gives a functor from Hilbert C*-modules over A to Hilbert…

Operator Algebras · Mathematics 2020-06-19 Tyrone Crisp

We calculate the Cuntz semigroup of the tensor product A with A. We restrict our attention to C*-algebras A which are unital, simple, nuclear, stably finite, have stable rank one, absorbs the Jiang-Su algebra tensorially and satisfy the…

Operator Algebras · Mathematics 2016-10-04 Cristian Ivanescu , Dan Kucerovsky

We investigate Keisler measures in arbitrary theories. Our initial focus is on Borel definability. We show that when working over countable parameter sets in countable theories, Borel definable measures are closed under Morley products and…

Logic · Mathematics 2023-06-28 Gabriel Conant , Kyle Gannon , James Hanson

We use product systems of $C^*$-correspondences to introduce twisted $C^*$-algebras of topological higher-rank graphs. We define the notion of a continuous $\mathbb{T}$-valued $2$-cocycle on a topological higher-rank graph, and present…

Operator Algebras · Mathematics 2021-07-30 Becky Armstrong , Nathan Brownlowe

We give a solution, via operator spaces, of an old problem in the Morita equivalence of C*-algebras. Namely, we show that C*-algebras are strongly Morita equivalent in the sense of Rieffel if and only if their categories of left operator…

Operator Algebras · Mathematics 2007-05-23 David P. Blecher

We show that group C*-algebras of finitely generated, nilpotent groups have finite nuclear dimension. It then follows, from a string of deep results, that the C*-algebra $A$ generated by an irreducible representation of such a group has…

Operator Algebras · Mathematics 2015-05-15 Caleb Eckhardt , Paul McKenney

A celebrated theorem of Pimsner states that a covariant representation $T$ of a $C^*$-correspondence $E$ extends to a $C^*$-representation of the Toeplitz algebra of $E$ if and only if $T$ is isometric. This paper is mainly concerned with…

Operator Algebras · Mathematics 2011-03-31 Ami Viselter

A C*-algebra $A$ is said to be stable if it is isomorphic to $A \otimes K(\ell_2)$. Hjelmborg and R\o rdam have shown that countable inductive limits of separable stable C*-algebras are stable. We show that this is no longer true in the…

Operator Algebras · Mathematics 2017-12-07 Saeed Ghasemi , Piotr Koszmider

We extend the classical Mercer theorem to reproducing kernel Hilbert spaces whose elements are functions from a measurable space $X$into $\mathbb C^n$. Given a finite measure $\mu$ on $X$, we represent the reproducing kernel $K$ as…

Functional Analysis · Mathematics 2011-10-19 Ernesto De Vito , Veronica Umanita` , Silvia Villa

We continue the study of the effective content of $K$-theory for C*-algebras, with a focus on AF algebras. We show that from a c.e. presentation of an AF algebra it is possible to compute a representation of the algebra as an inductive…

Operator Algebras · Mathematics 2026-02-09 Christopher J. Eagle , Isaac Goldbring , Timothy H. McNicholl

In 2014, Rieffel introduced norms on certain unital C*-algebras built from conditional expectations onto unital C*-subalgebras. We begin by showing that these norms generalize the Frobenius norm, and we provide explicit formulas for certain…

Operator Algebras · Mathematics 2022-06-02 Konrad Aguilar , Stephan Ramon Garcia , Elena Kim

A cosystem consists of a possibly nonselfadoint operator algebra equipped with a coaction by a discrete group. We introduce the concept of C*-envelope for a cosystem; roughly speaking, this is the smallest C*-algebraic cosystem that…

Operator Algebras · Mathematics 2022-01-27 Adam Dor-On , Evgenios T. A. Kakariadis , Elias G. Katsoulis , Marcelo Laca , Xin Li

We show the singular ideal in a non-Hausdorff \'etale groupoid C*-algebra is zero if and only if every unit is contained, at the level of group representation theory, in the collection of subgroups of the unit's isotropy group obtained as…

Operator Algebras · Mathematics 2025-10-28 Jeremy B. Hume

In this paper, the tensor product of highest weight modules with intermediate series modules over the Neveu-Schwarz algebra is studied. The weight spaces of such tensor products are all infinitely dimensional if the highest weight module is…

Rings and Algebras · Mathematics 2013-11-01 Xiufu Zhang

We revisit the results of Kim, and of Katsoulis and Ramsey concerning hyperrigidity for non-degenerate C*-correspondences. We show that the tensor algebra is hyperrigid, if and only if Katsura's ideal acts non-degenerately, if and only if…

Operator Algebras · Mathematics 2026-03-02 Joseph A. Dessi , Evgenios T. A. Kakariadis , Ioannis Apollon Paraskevas

We study the K-theory of the Cuntz-Nica-Pimsner C*-algebra of a rank-two product system that is an extension determined by an invariant ideal of the coefficient algebra. We use a construction of Deaconu and Fletcher that describes the…

Operator Algebras · Mathematics 2025-08-26 Astrid an Huef , Abraham C. S. Ng , Aidan Sims

In this article, we discuss the weak centrality of the tensor product $A\otimes_\alpha B$ of $C^\ast$-algebras $A$ and $B$ in terms of the weak centrality of $A$ and $B$, where $\alpha$ is either the Haagerup or the Banach space projective…

Functional Analysis · Mathematics 2025-08-13 Anmol Paliwal , Ranjana Jain

We show that given a rigid C*-tensor category, there is an equivalence of categories between normalized irreducible Q-systems, also known as connected unitary Frobenius algebra objects, and compact connected W*-algebra objects. Although…

Operator Algebras · Mathematics 2017-07-10 Corey Jones , David Penneys

By computing the completely bounded norm of the flip map on the Haagerup tensor product $C_0 Y_1\otimes_{C_0 X} C_0 Y_2$ associated to a pair of continuous mappings of locally compact Hausdorff spaces $Y_1\rightarrow X\leftarrow Y_2$, we…

Operator Algebras · Mathematics 2020-12-04 Tyrone Crisp