Parameterizing Hecke algebra modules: Bernstein-Zelevinsky multisegments, Kleshchev multipartitions, and crystal graphs

Abstract

This paper provides a combinatorial dictionary between three sets of objects: Bernstein-Zelevinsky multisegments, Kleshchev multipartitions, and the irreducible modules of the affine Hecke algebra $H_n$ (for generic $q$). In particular, we compute the action of the crystal operator $\tilde{e}_i$ (a refinement of socle of Restriction) on an irreducible module both in terms of its parameterization by multisegments and by multipartitions. In other words, we give explicit crystal graph isomorphisms. A byproduct is the determination of which multisegments parameterize modules of the {\it cyclotomic} Hecke algebra $H_n^λ$. The theorems also explain why the rule for computing $\tilde{e}_i$ mirrors the rule we know for that on a tensor product of crystal graphs. We also give a construction of the irreducible module parameterized by a multipartition without relying on a choice of path in the crystal graph. The proofs given here are elementary and do not rely on any geometry.