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April 06, 2009
Monday, April 06
Geometry and Topology
Time: 15:30
Speaker: Rick Jardine (Western)
Title: "Pointed torsors and Galois groups"
Room: MC 107

Abstract: Suppose that H is an algebraic group which is defined over a field k, and let L be the algebraic closure of k. The canonical stalk for the etale topology on k induces a simplicial set map from the classifying space B(H-tors) of the groupoid of H-torsors (aka. principal H-bundles) to the space BH(L). The homotopy fibres of this map are groupoids of pointed torsors, suitably defined. These fibres can be analyzed with cocycle techniques: their path components are representations of the absolute Galois groupoid in H, and each path component is contractible. The arguments for these results are simple, and applications will be displayed.