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Publication

Irreducible disconnected subgroups of exceptional algebraic groups

Soumaïa Nadia Ghandour
2010
Journal paper

Abstract

This paper studies the irreducible embeddings of simple algebraic groups of exceptional type. It is motivated by the role of such embeddings in the study of positive dimensional closed subgroups of classical algebraic groups. In this paper we give a classification of all triples where Y is a simple algebraic group of exceptional type, defined over an algebraically closed field K of characteristic , G is a closed disconnected positive dimensional subgroup of Y and V is a nontrivial rational irreducible KY-module on which G acts irreducibly.

Official source

https://infoscience.epfl.ch/record/268019?ln=en

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Related publications (7)

This dissertation is concerned with the study of irreducible embeddings of simple algebraic groups of exceptional type. It is motivated by the role of such embeddings in the study of positive dimensional closed subgroups of classical algebraic groups. The classification of the maximal closed connected subgroups of simple algebraic groups was carried out by E. B. Dynkin, G. M. Seitz and D. M. Testerman. Their analysis for the classical groups was based primarily on a striking result: if G is a simple algebraic group and ø : G → SL(V ) is a tensor indecomposable irreducible rational representation then, with specified exceptions, the image of G is maximal among closed connected subgroups of one of the classical groups SL(V), Sp(V ) or SO(V ). In the case of closed, not necessarily connected, subgroups of the classical groups, one is interested in considering irreducible embeddings of simple algebraic groups and their automorphism groups: given a simple algebraic group Y defined over an algebraically closed field K, one is led to study the embeddings G < Aut(Y ), where G and Aut(Y ) are closed subgroups of SL(V ) and V is an irreducible rational KY -module on which G acts irreducibly. A partial analysis of such embeddings in the case of classical algebraic groups Y was carried out by B. Ford. We purpose to classify all triples (G, Y, V ) where Y is a simple algebraic group of exceptional type, defined over an algebraically closed field K of characteristic p > 0, G is a closed non-connected positive dimensional subgroup of Y and V is a nontrivial irreducible rational KY -module such that V|G is irreducible. We obtain a precise description of such triples (G, Y, V ).

EPFL2008

Restricting representations of classical algebraic groups to maximal subgroups

Mikaël Cavallin

Fix an algebraically closed field

K

having characteristic

p\geq 0

and let

Y

be a simple algebraic group of classical type over

K.

Also let

X

be maximal among closed connected subgroups of

Y

and consider a non-trivial

p

-restricted irreducible rational

KY

-module

V.

In this thesis, we investigate the triples

(Y,X,V)

such that

X

acts with exactly two composition factors on

V

and see how it generalizes a question initially investigated by Dynkin in the

1950

s and then studied by numerous mathematicians. In particular, we study the natural embeddings of

\mbox{SO}_{2n}(K)

in both

\mbox{Spin}_{2n+1}(K)

and

\mbox{SL}_{2n}(K)

and obtain results on the structure of certain Weyl modules.

EPFL2015

On irreducible subgroups of simple algebraic groups

Claude Marion, Donna Testerman

Let G be a simple algebraic group over an algebraically closed field K of characteristic p >= 0, let H be a proper closed subgroup of G and let V be a nontrivial irreducible KG-module, which is p-restricted, tensor indecomposable and rational. Assume that the restriction of V to H is irreducible. In this paper, we study the triples (G, H, V) of this form when G is a classical group and H is positive-dimensional. Combined with earlier work of Dynkin, Seitz, Testerman and others, our main theorem reduces the problem of classifying the triples (G, H, V) to the case where G is an orthogonal group, V is a spin module and H normalizes an orthogonal decomposition of the natural KG-module.

Springer Heidelberg2017