Brion, M. Représentations exceptionnelles des groupes semi-simples. (French) Zbl 0588.22010 Ann. Sci. Éc. Norm. Supér. (4) 18, 345-387 (1985). In this paper the rational representations \(\phi\) : \(G\to GL(V)\) are studied, where V is a finite dimensional vector space and G is a semisimple group over \({\mathbb{C}}\) satisfying the following condition: the algebra \({\mathbb{C}}[V]^ U\) of U-invariant functions on V, where U is a maximal unipotent subgroup of G, is free. In this case V and the corresponding representation are called exceptional. In the first part of the paper the closure of G-orbits in V are characterized. The second part of the paper is devoted to the classification of exceptional representations of simple groups. In the third part it is established that all singularities of the variety \(\overline{Gx}\), \(x\in V\), lie in its boundary. [The results of this paper were announced in C. R. Acad. Sci., Paris, Sér. I 296, 5-6 (1983; Zbl 0538.14007)]. Reviewer: G.A.Soifer Cited in 1 ReviewCited in 27 Documents MSC: 22E46 Semisimple Lie groups and their representations 14L24 Geometric invariant theory 20G05 Representation theory for linear algebraic groups 14J17 Singularities of surfaces or higher-dimensional varieties Keywords:rational representations; semisimple group; exceptional representations; simple groups; singularities Citations:Zbl 0538.14007 PDF BibTeX XML Cite \textit{M. Brion}, Ann. Sci. Éc. Norm. Supér. (4) 18, 345--387 (1985; Zbl 0588.22010) Full Text: DOI Numdam Numdam EuDML References: [1] G. SCHWARZ , Representations of Simple Lie Groups with Regular Rings of Invariants (Invent. Math., vol. 49, 1978 , p. 167-191). MR 80m:14032 | Zbl 0391.20032 · Zbl 0391.20032 [2] G. SCHWARZ , Representations of Simple Lie Groups with a Free Module of Covariants (invent. Math., vol. 50, 1978 , p. 1-12). MR 80c:14008 | Zbl 0391.20033 · Zbl 0391.20033 [3] V. KAČ , Some Remarks on Nilpotent Orbits (J. 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