On Lens Spaces and Their Symplectic Fillings

Abstract

The standard contact structure on the three-sphere is invariant under the action of the cyclic group of order p yielding the lens space L(p,q). Therefore, every lens space carries a natural quotient contact structure Q. A theorem of Eliashberg and McDuff classifies the symplectic fillings of (L(p,1), Q) up to diffeomorphism. We announce a generalization of that result to every lens space. In particular, we give an explicit handlebody decomposition of every symplectic filling of (L(p,q), Q) for every p and q. Our results imply that: (a) there exist infinitely many lens spaces L(p,q) with q>1 such that (L(p,q), Q) admits only one symplectic filling up to blowup and diffeomorphism; (b) for any natural number N, there exist infinitely many lens spaces L(p,q) such that (L(p,q), Q) admits more than N symplectic fillings up to blowup and diffeomorphism.