Classification of group subschemes in , that contain a split maximal torus.
Cohomologial dimension of Laumon 1-motives up to isogenies
We prove that the category of Laumon 1-motives up to isogenies over a field of characteristic zero is of cohomological dimension . As a consequence this implies the same result for the category of formal Hodge structures of level (over ).
Cohomology of infinitesimal algebraic groups.
Cohomology of Infinitesimal and Discrete Groups.
Comparison between the fundamental group scheme of a relative scheme and that of its generic fiber
We show that the natural morphism between the fundamental group scheme of the generic fiber of a scheme over a connected Dedekind scheme and the generic fiber of the fundamental group scheme of is always faithfully flat. As an application we give a necessary and sufficient condition for a finite, dominated pointed -torsor over to be extended over . We finally provide examples where is an isomorphism.
Construction d'un groupe de Kac-Moody et applications
Contractions of Lie algebras and algebraic groups
Degenerations, contractions and deformations of various algebraic structures play an important role in mathematics and physics. There are many different definitions and special cases of these notions. We try to give a general definition which unifies these notions and shows the connections among them. Here we focus on contractions of Lie algebras and algebraic groups.
Correspondencias divisoriales entre esquemas relativos.
En este trabajo se estudian las correspondencias divisoriales entre dos esquemas relativos. Una correspondencia divisorial es una correspondencia algebraica entre los puntos de un esquema X y las clases de equivalencia lineal de divisores de otro esquema Y. Se consideran correspondencias triviales las que asignan a cada punto toda la variedad y las inversas de éstas. Por tanto las correspondencias divisoriales módulo las triviales son los divisores del producto módulo, módulo los divisores que provienen...
Corrigendum to : « Tame stacks in positive characteristic »
Courbes sur une variété abélienne
Cubic structures and ideal class groups