Ribbon cobordisms between lens spaces

Abstract

We determine when there exists a ribbon rational homology cobordism between two connected sums of lens spaces, i.e. one without $3$-handles. In particular, we show that if a lens space $L$ admits a ribbon rational homology cobordism to a different lens space, then $L$ must be homeomorphic to $L(n,1)$, up to orientation-reversal. As an application, we classify ribbon $\chi$-concordances between connected sums of $2$-bridge links. Our work builds on Lisca's work on embeddings of linear lattices.