Hook formulas for skew shapes I. $q$-analogues and bijections

Abstract

The celebrated hook-length formula gives a product formula for the number of standard Young tableaux of a straight shape. In 2014, Naruse announced a more general formula for the number of standard Young tableaux of skew shapes as a positive sum over excited diagrams of products of hook-lengths. We give an algebraic and a combinatorial proof of Naruse's formula, by using factorial Schur functions and a generalization of the Hillman--Grassl correspondence, respectively. The main new results are two different $q$-analogues of Naruse's formula: for the skew Schur functions, and for counting reverse plane partitions of skew shapes. We establish explicit bijections between these objects and families of integer arrays with certain nonzero entries, which also proves the second formula.

This is the main part of the first version of "Hook formulas for skew shapes". It contains the statements and proofs, and comparison with other formulas. The relations with q-Euler numbers and Dyck paths are now part of "Hook formulas for skew shapes II". v4. Typos and edits fixed, v5. fixed minor typos in Prop. 4.6, clarified definition of flagged tableaux before Prop. 3.5