Affine dual equivalence and $k$-Schur functions

Abstract

The k-Schur functions were first introduced by Lapointe, Lascoux and Morse (2003) in the hopes of refining the expansion of Macdonald polynomials into Schur functions. Recently, an alternative definition for k-Schur functions was given by Lam, Lapointe, Morse, and Shimozono (2010) as the weighted generating function of starred strong tableaux which correspond with labeled saturated chains in the Bruhat order on the affine symmetric group modulo the symmetric group. This definition has been shown to correspond to the Schubert basis for the affine Grassmannian of type A by Lam (2008), and, at t = 1, it is equivalent to the k-tableaux characterization of Lapointe and Morse (2007). In this paper, we extend Haiman's (1992) dual equivalence relation on standard Young tableaux to all starred strong tableaux. The elementary equivalence relations can be interpreted as labeled edges in a graph which share many of the properties of Assaf's dual equivalence graphs. These graphs display much of the complexity of working with k-Schur functions and the interval structure on affine Symmetric Group modulo the Symmetric Group. We introduce the notions of flattening and squashing skew starred strong tableaux in analogy with jeu da taquin slides in order to give a method to find all isomorphism types for affine dual equivalence graphs of rank 4. Finally, we make connections between k-Schur functions and both LLT and Macdonald polynomials by comparing the graphs for these functions.