V. Chernousov, Ph. Gille, Z. Reichstein, Resolving G-torsors by abelian base extensions, Journal of Algebra, 296 (2006), 561--581.

Abstract: Let G be a linear algebraic group defined over a field k. We prove that, under mild assumptions on k and G, there exists a finite k-subgroup S of G such that the natural map H^1(K, S) -> H^1(K, G) is surjective for every field extension K/k. We give two applications of this result in the case where k an algebraically closed field of characteristic zero and K/k is finitely generated. First we show that for every z in H^1(K, G) there exists an abelian field extension L/K such that z_L \in H^1(L, G) is represented by a G-torsor over a projective variety. In particular, we prove that z_L has trivial point obstruction. As a second application of our main theorem, we show that a (strong) variant of the algebraic form of Hilbert's 13th problem implies that the maximal abelian extension of K has cohomological dimension =< 1. The last assertion, if true, would prove conjectures of Bogomolov and Koenigsmann, answer a question of Tits and establish an important case of Serre's Conjecture II for the group E_8.

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