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The defect of strong approximation in connected linear groups. (Le défaut d’approximation forte dans les groupes linéaires connexes.) (French. English summary) Zbl 1216.11047
Summary: Let \(G\) be a connected linear algebraic group over a number field \(k\). We establish an exact sequence describing the closure of the group \(G(k)\) of rational points of \(G\) in the group of adelic points of \(G\). This exact sequence describes the defect of strong approximation on \(G\) in terms of the algebraic Brauer group of \(G\). In particular, we deduce from those results that the integral Brauer-Manin obstruction on a torsor under the group G is the only obstruction to the existence of an integral point on this torsor. We also obtain a non-abelian Poitou-Tate exact sequence for the Galois cohomology of the linear group \(G\). The main ingredients in the proof of those results are the local and global duality theorems for complexes of \(k\)-tori of length two and the abelianization maps in Galois cohomology introduced by Borovoi.

MSC:
11E72 Galois cohomology of linear algebraic groups
14L15 Group schemes
14G05 Rational points
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