Work

Decomposition numbers for unipotent blocks with small sl_2-weight in finite classical groups

Year: 2025

Type: article

Abstract: . We show that parabolic Kazhdan-Lusztig polynomials of type A compute the decomposition numbers in certain Harish-Chandra series of unipotent characters of finite groups of Lie types B, C and D over a field of non-defining odd characteristic l. Here, l is a “unitary prime” – the case that remains open in general, in the sense that it cannot be reduced to a similar problem for q-Schur algebras. The bipartitions labeling the characters in these series are small with respect to d, the order of q mod l, although they occur in blocks of arbitrarily high defect. Our main technical tool is the categorical action of an affine Lie algebra on the category of unipotent representations, which identifies the branching graph for Harish-Chandra induction with the sld-crystal on a sum of level 2 Fock spaces. Further key combinatorics has been adapted from Brundan and Stroppel’s work on Khovanov arc algebras to obtain the closed formula for the decomposition numbers in a d-small Harish- Chandra series.

Source: Kent Academic Repository (University of Kent)

Authors: Norton, Emily, Dudas, Olivier

Institutions: Centre National de la Recherche Scientifique, Aix-Marseille Université, Institut de Mathématiques de Marseille

Language: English

Topic: Finite Group Theory Research

Subfield: Discrete Mathematics and Combinatorics

Field: Mathematics

Domain: Physical Sciences

Open Access status: green

Funder: European Commission

Award: G7327996064

OpenAlex ID: W7130635653