Counting faces of graphical zonotopes

Abstract

It is a classical fact that the number of vertices of the graphical zonotope $Z_\Gamma$ is equal to the number of acyclic orientations of a graph $\Gamma$. We show that the $f$-polynomial of $Z_\Gamma$ is obtained as the principal specialization of the $q$-analog of the chromatic symmetric function of $\Gamma$.