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On Hilbert’s irreducibility theorem for linear algebraic groups. (English) Zbl 1509.12001

Summary: We complete the proof of a version of Hilbert’s irreducibility theorem for linear algebraic groups over a finitely generated field of characteristic 0, originally announced in [T. Bröcker and T. tom Dieck, Representations of compact Lie groups. New York, etc.: Springer-Verlag. (1985; Zbl 0581.22009)]. We also give a sample application to the existence of generic elements in Zariski dense subgroup of linear groups [G. Prasad and A. S. Rapinchuk, Int. Math. Res. Not. 2001, No. 23, 1229–1242 (2001; Zbl 1057.22025)].

MSC:

12E25 Hilbertian fields; Hilbert’s irreducibility theorem
11G35 Varieties over global fields
Full Text: DOI

References:

[1] By (1), the modulo n 2 reduction of .⇡ ı / 1 .OEnç⇠/ does not contain R 2 =n 2 D F l -points. It follows that ⇡ 1 .OEnç⇠/ does not contain k 2 -points (the reason is the same as the last three sentences of Step 1). In view of Lemma 4.2, the proof is com-plete.
[2] In the section, we prove the following result, which clearly implies Theorem 1.1. Theorem 5.1. Let G be a connected linear algebraic group over k, and let ⇢ G.k/ be a finitely generated Zariski dense subgroup. Let ⇡ W X ! G be a covering satisfying (PB). Then there is a finite-index coset of above which the fibres of ⇡ are irreducible. In particular, (HIT) holds for the pair .G; / over k.
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