Principal bundles of reductive groups over affine schemes, by Ivan Panin and Anastasia Stavrova

Let R be a semi-local regular domain containing an infinite perfect field k, and let K be the field of fractions of R. Let G be a reductive semi-simple simply connected R-group scheme such that each of its R-indecomposable factors is isotropic. We prove that for any Noetherian affine scheme A over k, the kernel of the map of etale cohomology sets H^1(A\times_k R,G) -> H^1(A\times_k K,G), induced by the inclusion of R into K, is trivial. If R is the semi-local ring of several points on a k-smooth scheme, then it suffices to require that k is infinite and keep the same assumption concerning G. The results extend the Serre--Grothendieck conjecture for such R and G, proved in K-theory preprint 929.

Ivan Panin <>
Anastasia Stavrova <>