On unitriangular basic sets for symmetric and alternating groups

Jean-Baptiste Gramain* (Corresponding Author), Olivier Brunat, Nicolas Jacon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We study the modular representation theory of the symmetric and alternating groups. One of the most natural ways to label the irreducible representations of a given group or algebra in the modular case is to show the unitriangularity of the decomposition matrices, that is, the existence of a unitriangular basic set. We study how the unitriangular basic sets of the alternating and the symmetric groups are related and obtain several results of existence. We show that these sets do not always exist in the case of the alternating groups by studying two explicit cases in characteristic 3. We then consider the case of a symmetric algebra and we show how one can obtain unitriangular basic sets in this more general context.
Original languageEnglish
Pages (from-to)257-292
Number of pages36
JournalJournal of Algebra
Early online date10 Jan 2023
Publication statusE-pub ahead of print - 10 Jan 2023


  • Basic set
  • Decomposition matrix of the alternative groups
  • decomposition matrix of the Hecke algebras


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