Titre: Cohomology of local systems and Siegel modular forms

G. Van der Geer (Amsterdam) exposé de novembre 2002

Résumé: This is joint work with Carel Faber (KTH, Stockholm). In the talk we will deal with the cohomology of local systems on the moduli space of curves of genus 2 and the moduli space of abelian surfaces. We describe explicitly the contributions from the boundary and endoscopy and we shall show how counting curves over finite fields provides us with detailed information about Siegel modular forms.