Embeddings of non-simply-connected 4-manifolds in 7-space. I. Classification modulo knots

We work in the smooth category. Let $N$ be a closed connected orientable 4-manifold with torsion free $H_1$, where $H_q:=H_q(N;Z)$. Our main result is a complete readily calculable classification of embeddings $N\to R^7$, up to the equivalence relation generated by isotopy and embedded connected sum with embeddings $S^4\to R^7$. Such a classification was already known only for $H_1=0$ by the work of Boéchat, Haefliger and Hudson from 1970. Our classification involves the Boéchat-Haefliger invariant $\varkappa(f)\in H_2$, Seifert bilinear form $λ(f):H_3\times H_3\to Z$ and $β$-invariant $β(f)$ which assumes values in a quotient of $H_1$ defined by values of $\varkappa(f)$ and $λ(f)$. In particular, for $N=S^1\times S^3$ we give a geometrically defined 1-1 correspondence between the set of equivalence classes of embeddings and an explicit quotient of the set $Z\oplus Z$. Our proof is based on development of Kreck modified surgery approach, involving some simpler reformulations, and also uses parametric connected sum.

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