arXiv subjects

Daniel W van Wyk

Publications and source records attributed to Daniel W van Wyk.

5 recordsLinked to original sources

arXiv2023

Characterizing Rickart and Baer ultragraph Leavitt path algebras

We characterize ultragraph Leavitt path algebras that are Rickart, locally Rickart, graded Rickart, and graded Rickart *-rings. We also characterize ultragraph Leavitt path algebras that are Baer, locally Baer, graded Baer, Baer *-rings, and combinations of these. These characterizations build on and generalize the work of Hazrat and Vas on Leavitt path algebras over fields to ultragraph Leavitt path algebras over semi-simple commutative unital rings.

math.RA↗

arXiv2020

Topological full groups of ultragraph groupoids as an isomorphism invariant

We prove two isomorphism-invariance theorems for groupoids associated with ultragraphs. These theorems characterize ultragraphs for which the topological full group of an associated groupoid is an isomorphism invariant. These results extend those of graph groupoids to ultragraph groupoids while providing another concrete example where the topological full group of a groupoid is a complete isomorphism invariant.

math.DS↗

arXiv2019

GCR and CCR Steinberg algebras

Kaplansky introduced the notions of CCR and GCR $C^*$-algebras because they have a tractable representation theory. Many years later, he introduced the notions of CCR and GCR rings. In this paper we characterize when the algebra of an ample groupoid over a field is CCR and GCR. The results turn out to be exact analogues of the corresponding characterization of locally compact groupoids with CCR and GCR $C^*$-algebras. As a consequence, we classify the CCR and GCR Leavitt path algebras.

math.OA↗

arXiv2018

The orbit spaces of groupoids whose $C^*$-algebras are CCR

Let G be second countable locally compact Hausdorff groupoid with a continuous Haar system. We remove the assumption of amenability in a theorem of Clark about groupoids whose $C^*$-algebras are CCR. We show that if the groupoid C*-algebra of G is CCR then the orbits of G are closed.

math.OA↗

arXiv2017

The orbit space of groupoids whose $C^*$-algebras are GCR

Let $G$ be second countable locally compact Hausdorff groupoid with a continuous Haar system. We remove the assumption of amenability in a theorem by Clark about GCR groupoid $C^*$-algebras. We show that if the groupoid $C^*$-algebra of $G$ is GCR then the orbits of $G$ are locally closed.

math.OA↗