manuscripta mathematica

, Volume 95, Issue 1, pp 169–180 | Cite as

Irreducibility of alternating and symmetric squares

  • Kay Magaard
  • Gunter Malle


We investigate the question when the alternating or symmetric square of an absolutely irreducible projective representation of a non-abelian simple groupG is again irreducible. The knowledge of such representations is of importance in the description of the maximal subgroups of simple classical groups of Lie type. We obtain complete results forG an alternating group and forG a projective special linear group when the given representation is in non-defining characteristic. For the proof we exhibit a linear composition factor in the socle of the restriction to a large subgroup of the alternating or symmetric square of a given projective representationV. Assuming irreducibility this shows that the dimension ofV has to be very small. A good knowledge of projective representations of small dimension allows to rule out these cases as well.

Mathematics Subject Classification (1991)

20E28 20G40 20C20 


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Copyright information

© Springer-Verlag 1998

Authors and Affiliations

  • Kay Magaard
    • 1
  • Gunter Malle
    • 2
  1. 1.Department of MathematicsWayne State UniversityDetroitUSA
  2. 2.IWR, Im Neuenheimer Feld 368Universität HeidelbergHeidelbergGermany

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