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Distinguished filtrations of the $0$-Hecke modules for dual immaculate quasisymmetric functions

Representation Theory 2025-01-22 v1 Combinatorics

Abstract

Let α\alpha range over the set of compositions. Dual immaculate quasisymmetric functions Sα\mathfrak{S}_\alpha^*, introduced by Berg, Bergeron, Saliola, Serrano, and Zabrocki, provide a quasisymmetric analogue of Schur functions. They also constructed an indecomposable 00-Hecke module Vα\mathcal{V}_\alpha whose image under the quasisymmetric characteristic is Sα\mathfrak{S}_\alpha^*. In this paper, we prove that Vα\mathcal{V}_\alpha admits a distinguished filtration with respect to the basis of Young quasisymmetric Schur functions. This result offers a novel representation-theoretic interpretation of the positive expansion of Sα\mathfrak{S}_\alpha^* in the basis of Young quasisymmetric Schur functions. A key tool in our proof is Mason's analogue of the Robinson-Schensted-Knuth algorithm, for which we establish a version of Green's theorem. As an unexpected byproduct of our investigation, we construct an indecomposable 00-Hecke module Yα\mathbf{Y}_\alpha whose image under the quasisymmetric characteristic is the Young quasisymmetric Schur function S^α\hat{\mathscr{S}}_\alpha. Further properties of this module are also investigated. And, by applying a suitable automorphism twist to this module, we obtain an indecomposable 00-Hecke module whose image under the quasisymmetric characteristic is the quasisymmetric Schur function Sα\mathscr{S}_\alpha.

Keywords

Cite

@article{arxiv.2501.11304,
  title  = {Distinguished filtrations of the $0$-Hecke modules for dual immaculate quasisymmetric functions},
  author = {So-Yeon Lee and Young-Tak Oh},
  journal= {arXiv preprint arXiv:2501.11304},
  year   = {2025}
}

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50 pages