Résumé : Using methods of motivic stable homotopy theory and the Chow-Witt groups, one can start to give invariants with values in quadratic forms that refine some of the common numerical invariants in algebraic geometry. This includes quadratic refinements of things like Euler charactaristics and degrees of Chern classes. We will give some details on these constructions and indicate how the six-functor formalism allows one to refine the foundations of modern enumerative geometry, specifically, the construction of the virtual fundamental class associated to a perfect obstruction theory, to refined classes in any cohomology theory of ``motivic type’’.
Lieu : Bât 425, Salle 117-119
Département de Mathématiques Bâtiment 425
Faculté des Sciences d'Orsay Université Paris-Sud
F-91405 Orsay Cedex
Tél. : +33 (0) 1-69-15-79-56