Positive scalar curvature and homology cobordism invariants

Abstract

We determine the local equivalence class of the Seiberg-Witten Floer stable homotopy type of a spin rational homology 3-sphere $Y$ embedded into a spin rational homology $S^{1} \times S^{3}$ with a positive scalar curvature metric so that $Y$ generates the third homology. The main tool of the proof is a relative Bauer-Furuta-type invariant on a periodic-end 4-manifold. As a consequence, we give obstructions to positive scalar curvature metrics on spin rational homology $S^{1} \times S^{3}$, typically described as the coincidence of various Frøyshov-type invariants. This coincidence also yields alternative proofs of two known obstructions by Jianfeng Lin and by the authors for the same class of 4-manifolds.