On the Shafarevich and Tate conjectures for hyperkähler varieties.
We classify all smooth projective varieties of degree 4 and describe their syzygies.
We classify quartic del Pezzo surface fibrations over the projective line via numerical invariants, giving explicit examples for small values of the invariants. For generic such fibrations, we describe explicitly the geometry of spaces of sections to the fibration, and mappings to the intermediate Jacobian of the total space. We exhibit examples where these are birational, which has applications to arithmetic questions, especially over finite fields.
In this paper we study the structure of manifolds that contain a quasi-line and give some evidence towards the fact that the irreducible components of degenerations of the quasi-line should determine the Mori cone. We show that the minimality with respect to a quasi-line yields strong restrictions on fibre space structures of the manifold.
La méthode de la descente a été introduite et développée par Colliot-Thélène et Sansuc. Elle permet d’étudier l’arithmétique de certaines variétés rationnelles. Dans ce texte on montre comment il en résulte que pour certaines familles de variétés rationnelles sur un corps local de caractéristique nulle le nombre des classes de -équivalence de la fibre est localement constant quand varie dans .