Kommende Vorträge

Given a family of smooth projective varieties, one can consider the relative de Rham moduli space, of flat vector bundles of rank n on the fibers. The flat vector bundles which underlie a Z-polarized variation of Hodge structure form the “non-abelian Hodge locus”. Simpson proved that this locus is closed and analytic, and he conjectured it is algebraic. Simpson's conjecture would imply a conjecture of Deligne that only finitely many representations of the fundamental group underlie a Z-PVHS on some fiber.

Two groups are elementarily equivalent if they have the same sets of true first order group theoretic sentences. We establish that if the homeomorphism groups of two compact connected manifolds are elementarily equivalent, then the manifolds are homeomorphic. This generalizes Whittaker's theorem on isomorphic homeomorphism groups (Ann. of Math. 1963) without relying on it. Our result also confirms a conjecture of M. Rubin (1989). We also show the analogous results for measure-preserving homeomorphism groups.