Chromatic nonsymmetric polynomials of Dyck graphs are slide-positive

Abstract

Motivated by the study of Macdonald polynomials, J. Haglund and A. Wilson introduced a nonsymmetric polynomial analogue of the chromatic quasisymmetric function called the chromatic nonsymmetric polynomial of a Dyck graph. We give a positive expansion for this polynomial in the basis of fundamental slide polynomials using recent work of Assaf-Bergeron on flagged ( P , ρ ) (P,\rho ) -partitions. We then derive the known expansion for the chromatic quasisymmetric function of Dyck graphs in terms of Gessel’s fundamental basis by taking a backstable limit of our expansion.