Kostant principal filtration and paths in weight lattices

Abstract

There are several interesting filtrations on the Cartan subalgebra of a complex simple Lie algebra coming from very different contexts: one is the principal filtration coming from the Langlands dual, one is coming from the Clifford algebra associated with a non-degenerate invariant bilinear form, one is coming from the symmetric algebra and the Chevalley projection, and two other ones are coming from the enveloping algebra and Harish-Chandra projections. It is now known that all these filtrations coincide. This results from a combination of works of several authors (Rohr, Joseph, Alekseev and the second named author), and was essentially conjectured by Kostant. In this paper, we establish a direct correspondence between the enveloping filtration and the symmetric filtration for a simple Lie algebra of type A or C. Our proof is very different from Rohr and Joseph approaches. The idea is to use an explicit description of the symmetric and enveloping invariants in term of combinatorial objects, called weighted paths, in the crystal graph of the standard representation.