Fractals on Graph Groupoids

We study the topological full group of ample groupoids over locally compact spaces. We extend Matui’s definition of the topological full group from the compact to the locally compact case. We provide two general classes of étale groupoids for which the topological full group, as an abstract group, is a complete isomorphism invariant, hereby extending Matui’s Isomorphism Theorem. As an application, we study graph groupoids and their topological full groups, and obtain sharper results for this class. The machinery developed in this process is used to prove an embedding theorem for ample groupoids, akin to Kirchberg’s Embedding Theorem for [Formula: see text]-algebras. Consequences for graph [Formula: see text]-algebras and Leavitt path algebras are also spelled out. In particular, we improve on a recent embedding theorem of Brownlowe and Sørensen for Leavitt path algebras.

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Orbit equivalence of graphs and isomorphism of graph groupoids

MATHEMATICA SCANDINAVICA ◽

10.7146/math.scand.a-105087 ◽

2018 ◽

Vol 123 (2) ◽

pp. 239-248 ◽

Cited By ~ 2

Author(s):

Toke Meier Carlsen ◽

Marius Lie Winger

Keyword(s):

Directed Graphs ◽

Periodic Points ◽

Path Space ◽

Orbit Equivalence ◽

Graph Groupoids ◽

Orbit Equivalent ◽

Boundary Path ◽

Isolated Points

We show that the groupoids of two directed graphs are isomorphic if and only if the two graphs are orbit equivalent by an orbit equivalence that preserves isolated eventually periodic points. We also give a complete description of the (topological) isolated points of the boundary path space of a graph. As a result, we are able to show that the groupoids of two directed graphs with finitely many vertices and no sinks are isomorphic if and only if the two graphs are orbit equivalent, and that the groupoids of the stabilisations of two such graphs are isomorphic if and only if the stabilisations of the graphs are orbit equivalent.

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