Lens spaces, rational balls and the ribbon conjecture

Abstract

We apply Donaldson's theorem on the intersection forms of definite 4--manifolds to characterize the lens spaces which smoothly bound rational homology 4--dimensional balls. Our result implies, in particular, that every smoothly slice 2--bridge knot is ribbon, proving the ribbon conjecture for 2--bridge knots.Comment: 45 pages, 8 figures; accepted for publication in Geometry and Topolog