Invariants de classes : propriétés fonctorielles et applications à l'étude du noyau

Abstract

The class-invariant homomorphism allows one to measure the Galois module structure of torsors--under a finite flat group scheme--which lie in the image of a coboundary map associated to an exact sequence. It has been introduced first by Martin Taylor (the exact sequence being given by an isogeny between abelian schemes). We begin by giving general properties of this homomorphism, then we pursue its study in the case when the exact sequence is given by the multiplication by $n$ on an extension of an abelian scheme by a torus.

19 pages, LaTeX. Minor changes