English

The projective cover of tableau-cyclic indecomposable $H_n(0)$-modules

Representation Theory 2022-09-08 v2 Combinatorics

Abstract

Let α\alpha be a composition of nn and σ\sigma a permutation in S(α)\mathfrak{S}_{\ell(\alpha)}. This paper concerns the projective covers of Hn(0)H_n(0)-modules Vα\mathcal{V}_\alpha, XαX_\alpha and Sασ\mathbf{S}^\sigma_{\alpha}, which categorify the dual immaculate quasisymmetric function, the extended Schur function, and the quasisymmetric Schur function when σ\sigma is the identity, respectively. First, we show that the projective cover of Vα\mathcal{V}_\alpha is the projective indecomposable module Pα\mathbf{P}_\alpha due to Norton, and XαX_\alpha and the ϕ\phi-twist of the canonical submodule Sβ,Cσ\mathbf{S}^{\sigma}_{\beta,C} of Sβσ\mathbf{S}^\sigma_{\beta} for (β,σ)(\beta,\sigma)'s satisfying suitable conditions appear as Hn(0)H_n(0)-homomorphic images of Vα\mathcal{V}_\alpha. Second, we introduce a combinatorial model for the ϕ\phi-twist of Sασ\mathbf{S}^\sigma_{\alpha} and derive a series of surjections starting from Pα\mathbf{P}_\alpha to the ϕ\phi-twist of Sα,Cid\mathbf{S}^{\mathrm{id}}_{\alpha,C}. Finally, we construct the projective cover of every indecomposable direct summand Sα,Eσ\mathbf{S}^\sigma_{\alpha, E} of Sασ\mathbf{S}^\sigma_{\alpha}. As a byproduct, we give a characterization of triples (σ,α,E)(\sigma, \alpha, E) such that the projective cover of Sα,Eσ\mathbf{S}^\sigma_{\alpha, E} is indecomposable.

Keywords

Cite

@article{arxiv.2008.06830,
  title  = {The projective cover of tableau-cyclic indecomposable $H_n(0)$-modules},
  author = {Seung-Il Choi and Young-Hun Kim and Sun-Young Nam and Young-Tak Oh},
  journal= {arXiv preprint arXiv:2008.06830},
  year   = {2022}
}

Comments

40 pages, Online published in TAMS

R2 v1 2026-06-23T17:53:03.507Z