Compactified Jacobians and q,t-Catalan numbers, II

Abstract

We continue the study of the rational-slope generalized $q,t$-Catalan numbers $c_{m,n}(q,t)$. We describe generalizations of the bijective constructions of J. Haglund and N. Loehr and use them to prove a weak symmetry property $c_{m,n}(q,1)=c_{m,n}(1,q)$ for $m=kn\pm 1$. We give a bijective proof of the full symmetry $c_{m,n}(q,t)=c_{m,n}(t,q)$ for $\min(m,n)\le 3$. As a corollary of these combinatorial constructions, we give a simple formula for the Poincar\'e polynomials of compactified Jacobians of plane curve singularities $x^{kn\pm 1}=y^n$. We also give a geometric interpretation of a relation between rational-slope Catalan numbers and the theory of $(m,n)$-cores discovered by J. Anderson.