Circle actions on simply connected $4$-manifolds
Circle actions on simply connected $4$-manifolds
Locally smooth ${S^1}$-actions on simply connected 4-manifolds are studied in terms of their weighted orbit spaces. An equivariant classification theorem is proved, and the weighted orbit space is used to compute the quadratic form of a given simply connected 4-manifold with ${S^1}$-action. This is used to show that a simply …