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

TL;DR

This paper constructs an unbounded Kasparov cycle for sphere embeddings into Euclidean space, computes its product with the Dirac operator, and verifies compatibility with bounded KK-theory, advancing the understanding of the shriek class in noncommutative geometry.

Contribution

It introduces a new unbounded Kasparov cycle for sphere embeddings and demonstrates its compatibility with the bounded Kasparov product, elucidating the composition law for the shriek map.

Findings

Constructed an explicit unbounded Kasparov cycle for sphere embeddings.

Computed the unbounded Kasparov product with the Euclidean Dirac operator.

Verified compatibility with bounded Kasparov product via Kucerovsky's criterion.

Abstract

We construct an unbounded representative for the shriek class associated to the embeddings of spheres into Euclidean space. We equip this unbounded Kasparov 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 $KK_0(\mathbb C, \mathbb C)$ 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.