A combinatorial formula for LLT cumulants of melting lollipops in terms of spanning trees

Abstract

We prove a combinatorial formula for LLT cumulants of melting lollipops as a positive combination of LLT polynomials indexed by spanning trees. The result gives an affirmative answer to a general positivity question for this class of unicellular LLT cumulants, and gives an independent proof of their Schur-positivity. In the special case of the complete graph, we also express the formula in terms of parking functions.Comment: An extended abstract of this work with fewer results and a different title is available at arXiv:2011.15080v