Exotic groupoid $C^{\ast }$-algebras associated to double groupoids

Abstract

We consider a class of partial action groupoids called double groupoids which are constructed from pairs of subgroups satisfying similar conditions to those of a matched pair of groups. If the double groupoid is étale, then we show that whenever the partially acting group admit exotic ideal completions in the sense of Brown and Guentner, the corresponding double groupoid also admit exotic $C^{\ast }$-completions.

17 pages; to appear in Math. Scand.; strengthened Example 4.1 by suggestion of the anonymous referee, fixed some typos and updated the bibliography