Counting homotopy classes of mappings via Dijkgraaf-Witten invariants

Abstract

Suppose $\Gamma$ is a finite group acting freely on $S^{n}$ ($n\geqslant 3$ being odd) and $M$ is any closed oriented $n$-manifold. We show that, given an integer $k$, the set $\deg^{-1}(k)$ of based homotopy classes of mappings with degree $k$ is finite and its cardinality depends only on the congruence class of $k$ modulo $\#\Gamma$; moreover, $\#\deg^{-1}(k)$ can be expressed in terms of the Dijkgraaf-Witten invariants of $M$.