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NONREALIZABILITY OF CERTAIN REPRESENTATIONS IN FUSION SYSTEMS

Published online by Cambridge University Press:  11 April 2023

BOB OLIVER*
Affiliation:
Université Sorbonne Paris Nord, LAGA, UMR 7539 du CNRS, 99, Av. J.-B. Clément, Villetaneuse 93430, France

Abstract

For a finite abelian p-group A and a subgroup $\Gamma \le \operatorname {\mathrm {Aut}}(A)$, we say that the pair $(\Gamma ,A)$ is fusion realizable if there is a saturated fusion system ${\mathcal {F}}$ over a finite p-group $S\ge A$ such that $C_S(A)=A$, $\operatorname {\mathrm {Aut}}_{{\mathcal {F}}}(A)=\Gamma $ as subgroups of $\operatorname {\mathrm {Aut}}(A)$, and . In this paper, we develop tools to show that certain representations are not fusion realizable in this sense. For example, we show, for $p=2$ or $3$ and $\Gamma $ one of the Mathieu groups, that the only ${\mathbb {F}}_p\Gamma $-modules that are fusion realizable (up to extensions by trivial modules) are the Todd modules and in some cases their duals.

Type
Research Article
Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of Australian Mathematical Publishing Association Inc.

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Footnotes

Communicated by Michael Giudici

B. Oliver is partially supported by UMR 7539 of the CNRS. Part of this work was carried out at the Isaac Newton Institute for Mathematical Sciences during the GRA2 programme, supported by EPSRC Grant No. EP/K032208/1.

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