DOCUMENTA MATHEMATICA, Vol. 21 (2016), 809-840

Charles Starling

C*-Algebras of Boolean Inverse Monoids -- Traces and Invariant Means

To a Boolean inverse monoid $S$ we associate a universal C*-algebra $C^*B(S)$ and show that it is equal to Exel's tight C*-algebra of $S$. We then show that any invariant mean on $S$ (in the sense of Kudryavtseva, Lawson, Lenz and Resende) gives rise to a trace on $C^*B(S)$, and vice-versa, under a condition on $S$ equivalent to the underlying groupoid being Hausdorff. Under certain mild conditions, the space of traces of $C^*B(S)$ is shown to be isomorphic to the space of invariant means of $S$. We then use many known results about traces of C*-algebras to draw conclusions about invariant means on Boolean inverse monoids; in particular we quote a result of Blackadar to show that any metrizable Choquet simplex arises as the space of invariant means for some AF inverse monoid $S$.

2010 Mathematics Subject Classification: 20M18, 46L55, 46L05

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