Pointed Torsors

Jardine, J. F.

Canadian journal of mathematics, Tome 63 (2011) no. 6, pp. 1345-1363

Résumé

This paper gives a characterization of homotopy fibres of inverse image maps on groupoids of torsors that are induced by geometric morphisms, in terms of both pointed torsors and pointed cocycles, suitably defined. Cocycle techniques are used to give a complete description of such fibres, when the underlying geometric morphism is the canonical stalk on the classifying topos of a profinite group $G$ . If the torsors in question are defined with respect to a constant group $H$ , then the path components of the fibre can be identified with the set of continuous maps from the profinite group $G$ to the group $H$ . More generally, when $H$ is not constant, this set of path components is the set of continuous maps from a pro-object in sheaves of groupoids to $H$ , which pro-object can be viewed as a “Grothendieck fundamental groupoid”.

Détail

DOI : 10.4153/CJM-2011-058-x

Mots-clés : 18G50, 14F35, 55B30, pointed torsors, pointed cocycles, homotopy fibres