New combinatorial formulations of the shuffle conjecture

The shuffle conjecture (due to Haglund, Haiman, Loehr, Remmel, and Ulyanov) provides a combinatorial formula for the Frobenius series of the diagonal harmonics module DHnDHn, which is the symmetric function ∇(en)∇(en). This formula is a sum over all labeled Dyck paths of terms built from combinatorial statistics called area, dinv, and IDes. We provide three new combinatorial formulations of the shuffle conjecture based on other statistics on labeled paths, parking functions, and related objects. Each such reformulation arises by introducing an appropriate new definition of the inverse descent set. Analogous results are proved for the higher-order shuffle conjecture involving ∇m(en)∇m(en). We also give new versions of some recently proposed combinatorial formulas for ∇(Cα)∇(Cα) and ∇(s(k,1(n−k)))∇(s(k,1(n−k))), which translate expansions based on the dinv statistic into equivalent expansions based on Haglund's bounce statistic.