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Given an ample Hausdorff groupoid $G$, a unital commutative ring $R$, and a discrete twist $(\Sigma,i,q)$, we establish a generalised uniqueness theorem for the twisted Steinberg algebra $A_R(G;\Sigma)$. By applying this theorem when $G$ is…

Rings and Algebras · Mathematics 2026-05-13 Rizalyn S. Bongcawel , Lyster Rey B. Cabardo , Lisa O. Clark

Given an ample, Hausdorff groupoid $\mathcal{G}$, and a unital commutative ring $R$, we consider the Steinberg algebra $A_R(\mathcal {G})$. First we prove a uniqueness theorem for this algebra and then, when $\mathcal{G}$ is graded by a…

Rings and Algebras · Mathematics 2016-09-12 Lisa Orloff Clark , Ruy Exel , Enrique Pardo

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

To each finitely aligned higher-rank graph $\Lambda$ and each $\mathbb{T}$-valued 2-cocycle on $\Lambda$, we associate a family of twisted relative Cuntz-Krieger algebras. We show that each of these algebras carries a gauge action, and…

Operator Algebras · Mathematics 2013-10-29 Benjamin Whitehead

We introduce twisted relative Cuntz-Krieger algebras associated to finitely aligned higher-rank graphs and give a comprehensive treatment of their fundamental structural properties. We establish versions of the usual uniqueness theorems and…

Operator Algebras · Mathematics 2014-08-07 Aidan Sims , Benjamin Whitehead , Michael F. Whittaker

We prove Cuntz-Krieger and graded uniqueness theorems for Steinberg algebras. We also show that a Steinberg algebra is basically simple if and only if its associated groupoid is both effective and minimal. Finally we use results of…

Rings and Algebras · Mathematics 2014-03-20 Lisa Orloff Clark , Cain Edie-Michell

We define the notion of a twisted topological graph algebra associated to a topological graph and a $1$-cocycle on its edge set. We prove a stronger version of a Vasselli's result. We expand Katsura's results to study twisted topological…

Operator Algebras · Mathematics 2019-02-20 Hui Li

We study homological invariants of the Steinberg algebra $\mathcal{A}_k(\mathcal{G})$ of an ample groupoid $\mathcal{G}$ over a commutative ring $k$. For $\mathcal{G}$ principal or Hausdorff with…

K-Theory and Homology · Mathematics 2025-05-29 Guido Arnone , Guillermo Cortiñas , Devarshi Mukherjee

Suppose $\mathcal{G}$ is a second-countable locally compact Hausdorff \'{e}tale groupoid, $G$ is a discrete group containing a unital subsemigroup $P$, and $c:\mathcal{G}\rightarrow G$ is a continuous cocycle. We derive conditions on the…

Operator Algebras · Mathematics 2019-06-10 Lisa Orloff Clark , James Fletcher

We show that if $G$ is a second countable locally compact Hausdorff \'etale groupoid carrying a suitable cocycle $c:G\to\mathbb{Z}$, then the reduced $C^*$-algebra of $G$ can be realised naturally as the Cuntz-Pimsner algebra of a…

Operator Algebras · Mathematics 2018-04-19 Adam Rennie , David Robertson , Aidan Sims

Let G be a locally compact, Hausdorff groupoid in which s is a local homeomorphism and the unit space is totally disconnected. Assume there is a continuous cocycle c from G into a discrete group $\Gamma$. We show that the collection A(G) of…

Rings and Algebras · Mathematics 2012-02-07 Lisa Orloff Clark , Cynthia Farthing , Aidan Sims , Mark Tomforde

In this note, we will show that the twisted convolution algebra $L^1_{\alpha,\omega}({\sf G},\mathfrak A)$ associated to a twisted action of a locally compact group ${\sf G}$ on a $C^*$-algebra $\mathfrak A$ has the following property:…

Functional Analysis · Mathematics 2025-10-16 Felipe I. Flores

We analyze the algebraic structures of G--Frobenius algebras which are the algebras associated to global group quotient objects. Here G is any finite group. These algebras turn out to be modules over the Drinfeld double of the group ring…

Algebraic Geometry · Mathematics 2007-05-23 Ralph M. Kaufmann

In this paper we will study the isomorphism problem for the reduced twisted group and groupoid $L^p$-operator algebras. For a locally compact group $G$ and a continuous 2-cocycle $\sigma$ we will define the reduced $\sigma$-twisted…

Functional Analysis · Mathematics 2023-05-29 Einar V. Hetland , Eduard Ortega

Let $A$ be a $k$-algebra where $k$ is an algebraically closed field and $G$ be a finite abelian group for which the characteristic of $k$ does not divide $|G|$. If $G$ acts on $A$ by $k$-algebra automorphisms then the action induces a…

Rings and Algebras · Mathematics 2015-02-24 Andrew Davies

We show how to recover a discrete twist over an ample Hausdorff groupoid from a pair consisting of an algebra and what we call a quasi-Cartan subalgebra. We identify precisely which twists arise in this way (namely, those that satisfy the…

We study self-similar groupoid actions on arbitrary directed graphs together with $\mathbb{T}$-valued twists that exhaust the second cohomology group of the associated Zappa-Sz\'ep product category. We define and analyse the associated…

Operator Algebras · Mathematics 2025-11-21 B. K. Kwaśniewski , A. Mundey

We prove a uniqueness theorem and give a characterization of simplicity for Steinberg algebras associated to non-Hausdorff ample groupoids. We also prove a uniqueness theorem and give a characterization of simplicity for the C*-algebra…

Operator Algebras · Mathematics 2019-05-17 Lisa Orloff Clark , Ruy Exel , Enrique Pardo , Aidan Sims , Charles Starling

Let $({\sf G},\alpha, \omega,\mathfrak B)$ be a measurable twisted action of the locally compact group ${\sf G}$ on a Banach $^*$-algebra $\mathfrak B$ and $\mathfrak A$ a differential Banach $^*$-subalgebra of $\mathfrak B$, which is…

Operator Algebras · Mathematics 2025-03-17 Felipe I. Flores

Given a field $K$ and an ample (not necessarily Hausdorff) groupoid $G$, we define the concept of a line bundle over $G$ inspired by the well known concept from the theory of C*-algebras. If $E$ is such a line bundle, we construct the…

Operator Algebras · Mathematics 2025-06-12 M. Dokuchaev , R. Exel , H. Pinedo
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