September 29, 2006

Michael Usher (Princeton)

Title: The topology of symplectic sums of four-manifolds.

Abstract: I will explain how the gluing formula for Gromov-Witten invariants gives rise to very general results about the topology of 4-manifolds obtained by normal connected sums along symplectic surfaces of positive genus. As a special case, the fiber sum of two nontrivial relatively minimal Lefschetz fibrations is minimal, as was conjectured by Stipsicz.