A refined twist on Hurwitz numbers

Abstract

We introduce a two-parameter refinement of the Jucys-Murphy theory, that we call the CJT-refinement, unifying Schur, zonal, and, conjecturally, Jack actions of the ring of symmetric functions on the Fock space. Applications of this formalism include a partial resolution of a recent conjecture of Coulter-Do, as well as cut-and-join recursion for $b$-Hurwitz numbers. The cut-and-join equations enable the derivation of the tropicalization of $b$--Hurwitz numbers. We also provide a first application of this tropical interpretation by answering an open problem of Chapuy-Dołęga on the polynomial structure of $b$-Hurwitz numbers.

65 pages, 10 figurs