All finite transitive graphs admit self-adjoint free semigroupoid algebras

In this paper we show that every non-cycle finite transitive directed graph has a Cuntz-Krieger family whose WOT-closed algebra is \(B(\mathcal{H})\). This is accomplished through a new construction that reduces this problem to in-degree \(2\)-regular graphs, which is then treated by applying the periodic Road Coloring Theorem of Béal and Perrin. As a consequence we show that finite disjoint unions of finite transitive directed graphs are exactly those finite graphs which admit self-adjoint free semigroupoid algebras.