Professor Susan Tolman, University of Illinois at Urbana-Champaign and MIT
The symplectic topology of Hamiltonian circle actions

Based on joint work with D. McDuff. Our work focusses on one aspect of the relationship between symplectic geometry and symplectic topology. More specifically, every symplectic circle action gives an element of the fundamental group of the group of symplectomorphisms. We use Gromov-Witten invariants to prove that,in many cases, this element is non-trivial.