Immersions and the unbounded Kasparov product: embedding spheres into Euclidean space

Abstract

We construct an unbounded representative for the shriek class associated to the embeddings of spheres into Euclidean space. We equip this unbounded $KK$-cycle with a connection and compute the unbounded Kasparov product with the Dirac operator on ${\mathbb{R}}^{n+1}$. We find that the resulting spectral triple for the algebra $C({\mathbb{S}}^n)$ differs from the Dirac operator on the round sphere by a so-called index cycle, whose class in $K{K}_0(\mathbb{C},\mathbb{C})$ represents the multiplicative unit. At all points we check that our construction involving the unbounded Kasparov product is compatible with the bounded Kasparov product using Kucerovsky’s criterion and we thus capture the composition law for the shriek map for these immersions at the unbounded $KK$-theoretical level, while retaining the geometric information.