Decomposition of tensor products of modular irreducible representations for SL3

Chris Bowman-Scargill, Stephen Doty, S Martin

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We give an algorithm for working out the indecomposable direct summands in a Krull–Schmidt decomposition of a tensor product of two simple modules for G = SL3 in characteristics 2 and 3. It is shown that there is a finite family of modules such that every such indecomposable summand is expressible as a twisted tensor product of members of that family. Along the way we obtain the submodule structure of various Weyl and tilting modules. Some of the tilting modules that turn up in characteristic 3 are not rigid; these seem to provide the first example of non-rigid tilting modules for algebraic groups. These non-rigid tilting modules lead to examples of non-rigid projective indecomposable modules for Schur algebras, as shown in the Appendix.
Original languageEnglish
Pages (from-to)177-219
Number of pages43
JournalInternational Electronic Journal of Algebra
Publication statusPublished - 1 Jan 2011

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