Transfer maps in generalized group homology via submanifolds

TL;DR

This paper constructs transfer maps in various generalized homology theories for submanifold embeddings, extending known results in KO-homology and ordinary homology, with applications to scalar curvature obstructions.

Contribution

It develops a unified framework for transfer maps in generalized homology theories for submanifold embeddings, generalizing previous results and simplifying proofs.

Findings

Constructs transfer maps in ordinary homology for all codimensions.

Establishes transfer maps in complex K-homology for codimension up to 3.

Provides transfer maps in equivariant KO-homology for codimension up to 2.

Abstract

Let $N \subset M$ be a submanifold embedding of spin manifolds of some codimension $k \geq 1$. A classical result of Gromov and Lawson, refined by Hanke, Pape and Schick, states that $M$ does not admit a metric of positive scalar curvature if $k = 2$ and the Dirac operator of $N$ has non-trivial index, provided that suitable conditions are satisfied. In the cases $k=1$ and $k=2$, Zeidler and Kubota, respectively, established more systematic results: There exists a transfer $\mathrm{KO}_\ast(\mathrm{C}^{\ast} \pi_1 M)\to \mathrm{KO}_{\ast - k}(\mathrm{C}^\ast \pi_1 N)$ which maps the index class of $M$ to the index class of $N$. The main goal of this article is to construct analogous transfer maps $E_\ast(\mathrm{B}\pi_1M) \to E_{\ast-k}(\mathrm{B}\pi_1N)$ for different generalized homology theories $E$ and suitable submanifold embeddings. The design criterion is that it is compatible with the transfer $E_\ast(M) \to E_{\ast-k}(N)$ induced by the inclusion $N \subset M$ for a chosen orientation on the normal bundle. Under varying restrictions on homotopy groups and the normal bundle, we construct transfers in the following cases in particular: In ordinary homology, it works for all codimensions. This slightly generalizes a result of Engel and simplifies his proof. In complex K-homology, we achieve it for $k \leq 3$. For $k \leq 2$, we have a transfer on the equivariant KO-homology of the classifying space for proper actions.