Séminaire Lotharingien de Combinatoire, 78B.74 (2017), 12 pp.

Brittney Ellzey

Chromatic Quasisymmetric Functions of Directed Graphs

Abstract. Chromatic quasisymmetric functions of labeled graphs were defined by Shareshian and Wachs as a refinement of Stanley's chromatic symmetric functions. In this extended abstract, we consider an extension of their definition from labeled graphs to directed graphs, suggested by Richard Stanley. We obtain an F-basis expansion of the chromatic quasisymmetric functions of all digraphs and a p-basis expansion for all symmetric chromatic quasisymmetric functions of digraphs, extending work of Shareshian-Wachs and Athanasiadis. We show that the chromatic quasisymmetric functions of proper circular arc digraphs are symmetric functions, which generalizes a result of Shareshian and Wachs on natural unit interval graphs. The directed cycle on n vertices is contained in the class of proper circular arc digraphs, and we give a generating function for the e-basis expansion of the chromatic quasisymmetric function of the directed cycle, refining a result of Stanley for the undirected cycle. We present a generalization of the Shareshian-Wachs refinement of the Stanley-Stembridge e-positivity conjecture.

Received: November 14, 2016. Accepted: February 17, 2017. Final version: April 1, 2017.

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