Chromatic numbers and a Lov\'asz type inequality for non-commutative graphs

Abstract

Non-commutative graph theory is an operator space generalization of graph theory. Well known graph parameters such as the independence number and Lov\'asz theta function were first generalized to this setting by Duan, Severini, and Winter. We introduce two new generalizations of the chromatic number to non-commutative graphs and provide a generalization of the Lov\'asz sandwich inequality. In particular, we show the chromatic number of the orthogonal complement of a non-commutative graph is bounded below by its theta number. We also provide a generalization of both Sabadussi's Theorem and Hedetniemi's conjecture to non-commutative graphs.