Free Semigroupoid Algebras from Categories of Paths

Authors

Juliana Bukoski, University of Nebraska-LincolnFollow

First Advisor

Allan Donsig

Date of this Version

4-2021

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Mathematics, Under the Supervision of Professor Allan Donsig. Lincoln, Nebraska: May, 2021

Copyright © 2021 Juliana Bukoski

Abstract

Given a directed graph G, we can define a Hilbert space H_G with basis indexed by the path space of the graph, then represent the vertices of the graph as projections on H_G and the edges of the graph as partial isometries on H_G. The weak operator topology closed algebra generated by these projections and partial isometries is called the free semigroupoid algebra for G. Kribs and Power showed that these algebras are reflexive, and that they are semisimple if and only if each path in the graph lies on a cycle. We extend the free semigroupoid algebra construction to categories of paths, which are a generalization of graphs, and provide examples of free semigroupoid algebras from categories of paths that cannot arise from graphs (or higher rank graphs). We then describe conditions under which these algebras are semisimple, and we prove reflexivity for a class of examples.

Adviser: Allan Donsig