Smith-Gysin Sequence

Abstract

Starting with a manifold $M$ and a semi-free action of $S^3$ on it, we have the Smith-Gysin sequence: $$ \cdots \to H^{*}( M) \to H^{*-3}(M/S^3, M^{S^3}) \oplus H^{*} (M^{S^3}) \to H^{*+1}(M/S^3, M^{S^3}) \to H^{*+1}(M) \to \cdots $$ In this paper, we construct a Smith-Gysin sequence that does not require the semi-free condition. This sequence includes a new term, referred to as the "exotic term," which depends on the subset $M^{S^1}$: $$ \cdots \to H^{*}(M) \to H^{*-3} (M/S^3, \Sigma/S^3) \oplus H^{*}(M^{S^3}) \oplus \left( H^{*-2}(M^{S^1})\right)^{-\mathbb{Z}_2} \to H^{*+1}(M/S^3,M^{S^3}) \to H^{*+1}(M) \to \cdots $$ Here, $\Sigma \subset M$ is the subset of points in $M$ whose isotropy groups are infinite. The group $\mathbb{Z}_2$ acts on $M^{S^1}$ by $j \in S^3$.