New interpretations for Kromatic symmetric function expansions

Source abstract

The Kromatic symmetric function (KSF) $\overline{X}_{G}$, introduced by Crew, Pechenik, and Spirkl (2026), is a $K$-theoretic analogue of the chromatic symmetric function (CSF) $X_G$. We study expansion formulas for the KSF in two different bases. First, we explore recursive ways to compute the KSF's expansion in the $K$-theoretic monomial symmetric function basis $\overline{\widetilde{m}}_λ$, generalizing formulas that were used by the second author and Samanta to show that the KSF distinguishes certain families of graphs that are not distinguished by the CSF. Second, we give new interpretations for the KSF's expansion in the $K$-theoretic power sum basis $\overline{p}_λ$, using an inclusion-exclusion approach like the one from Stanley (1995) instead of an acyclic orientation approach. Finally, we give $K$-analogues of Schmitt's and of Humpert and Martin's antipode formulas for the Hopf algebra of graphs, along with a Hopf algebra interpretation for both the $\overline{p}$-expansion and $\overline{\widetilde{m}}$-expansion of the KSF.