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To a representation of $\O_N$ (the Cuntz algebra with $N$ generators) we associate a projection valued measure and we study the case when this measure has atoms. The main technical tool are the spaces invariant for all the operators…

Operator Algebras · Mathematics 2013-11-22 Dorin Ervin Dutkay , John Haussermann , Palle E. T. Jorgensen

We provide formulas for computing the discriminant of noncommutative algebras over central subalgebras in the case of Ore extensions and skew group extensions. The formulas follow from a more general result regarding the discriminants of…

Rings and Algebras · Mathematics 2018-09-28 Jason Gaddis , Ellen Kirkman , W. Frank Moore

According to the Hall algebras of quivers with automorphisms under Lusztig's construction, the polynominal forms of several structure coefficients for quantum groups of all finite types are presented in this note. We first provide a…

Representation Theory · Mathematics 2025-10-30 Yixin Lan , Yumeng Wu , Jie Xiao

We give an elementary characterization of those (abelian) semigroups $M$ that are direct limits of countable sequences of finite direct products of monoids of the form $C\cup\{0\}$ for monogenic groups $C$. This characterization involves…

Operator Algebras · Mathematics 2007-05-23 Enrique Pardo , Friedrich Wehrung

We introduce and study the definition, main properties and applications of iterated twisted tensor products of algebras, motivated by the problem of defining a suitable representative for the product of spaces in noncommutative geometry. We…

Quantum Algebra · Mathematics 2016-08-16 P. Jara Martínez , J. López Peña , F. Panaite , F. Van Oystaeyen

Let k be a field, q in k. We derive a cup product formula on the Hochschild cohomology ring of a family Lambda_q of quiver algebras. Using this formula, we determine a subalgebra of k[x,y] isomorphic to Hochschild cohomology modulo N, where…

Rings and Algebras · Mathematics 2020-04-03 Tolulope Oke

We define solvable quantum mechanical systems on a Hilbert space spanned by bipartite ribbon graphs with a fixed number of edges. The Hilbert space is also an associative algebra, where the product is derived from permutation group…

High Energy Physics - Theory · Physics 2023-07-17 Joseph Ben Geloun , Sanjaye Ramgoolam

In this paper we show that the Cuntz--Pimsner algebras associated to minimal homeomorphisms twisted by line bundles, along with their orbit-breaking subalgebras, are $\mathcal{Z}$-stable whenever the underlying dynamical system has the…

Operator Algebras · Mathematics 2025-11-25 Marzieh Forough , Ja A Jeong , Karen R. Strung

Given a semisimple compact Lie group $G$ and a nonzero dominant integral weight $\lambda$, the highest weight $G_q$-modules $V_{n\lambda}$ form a subproduct system of finite dimensional Hilbert spaces. Using a conjectural asymptotic…

Operator Algebras · Mathematics 2025-12-22 Suvrajit Bhattacharjee , Olof Giselsson , Sergey Neshveyev

In this paper, we consider topological semigroup actions on compact topological spaces. Under mild assumptions on the semigroup and the action, we construct a semi-direct product groupoid with a Haar system. We also show that it is…

Operator Algebras · Mathematics 2014-06-20 Jean Renault , S. Sundar

Let G be the wreath product of Z and Z/2, the so called lamplighter group and k a commutative ring. We show that kG does not have a classical ring of quotients (i.e. does not satisfy the Ore condition). This answers a Kourovka notebook…

Rings and Algebras · Mathematics 2018-11-28 Peter Linnell , Wolfgang Lueck , Thomas Schick

For any ring $R$, we introduce an invariant in the form of a partially ordered abelian semigroup $\mathrm{S}(R)$ built from an equivalence relation on the class of countably generated projective modules. We call $\mathrm{S}(R)$ the Cuntz…

Rings and Algebras · Mathematics 2023-07-17 Ramon Antoine , Pere Ara , Joan Bosa , Francesc Perera , Eduard Vilalta

We propose a new non-commutative generalization of the representation variety and the character variety of a knot group. Our strategy is to reformulate the construction of the algebra of functions on the space of representations in terms of…

Geometric Topology · Mathematics 2022-12-01 Jun Murakami , Roland van der Veen

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 introduce a nonsymmetric, associative tensor product among representations of Cuntz algebras by using embeddings. We show the decomposition formulae of tensor products for permutative representations explicitly We apply decomposition…

Operator Algebras · Mathematics 2007-05-23 Katsunori Kawamura

In this paper we prove a family of results connecting the problem of computing cup products in surface bundles to various other objects that appear in the theory of the cohomology of the mapping class group $\operatorname{Mod}_g$ and the…

Geometric Topology · Mathematics 2016-01-29 Nick Salter

In this article we consider orthonormal systems consisting of tensor products of splines. We show some convergence results of the corresponding orthogonal series including a.e. convergence and unconditional convergence in $L^p$ for…

Classical Analysis and ODEs · Mathematics 2022-04-05 M. Passenbrunner

The algebraic Cuntz-Pimsner rings are naturally $\mathbb{Z}$-graded rings that generalize both Leavitt path algebras and unperforated $\mathbb{Z}$-graded Steinberg algebras. We classify strongly, epsilon-strongly and nearly epsilon-strongly…

Rings and Algebras · Mathematics 2019-09-24 Daniel Lännström

Topological quivers generalize the notion of directed graphs in which the sets of vertices and edges are locally compact (second countable) Hausdorff spaces. Associated to a topological quiver $Q$ is a $C^*$-correspondence, and in turn, a…

Operator Algebras · Mathematics 2013-01-31 Shawn J. McCann

We construct a covariant functor from the topological torus bundles to the so-called Cuntz-Krieger algebras; the functor maps homeomorphic bundles into the stably isomorphic Cuntz-Krieger algebras. It is shown, that the K-theory of the…

Operator Algebras · Mathematics 2011-02-21 Igor Nikolaev