On the Unbounded Picture of $KK$-Theory

Abstract

In the founding paper on unbounded $KK$-theory it was established by Baaj and Julg that the bounded transform, which associates a class in $KK$-theory to any unbounded Kasparov module, is a surjective homomorphism (under a separability assumption). In this paper, we provide an equivalence relation on unbounded Kasparov modules and we thereby describe the kernel of the bounded transform. This allows us to introduce a notion of topological unbounded $KK$-theory, which becomes isomorphic to $KK$-theory via the bounded transform. The equivalence relation is formulated entirely at the level of unbounded Kasparov modules and consists of homotopies together with an extra degeneracy condition. Our degenerate unbounded Kasparov modules are called spectrally decomposable since they admit a decomposition into a part with positive spectrum and a part with negative spectrum.

References in corpus (3)

• Sums of regular selfadjoint operators in Hilbert-C*-modules
• Morita invariance of unbounded bivariant K-theory
• Factorization of Dirac operators on toric noncommutative manifolds

Cited by in corpus (5)

• Spectral localizer for line-gapped non-hermitian systems
• Gauge theory on noncommutative Riemannian principal bundles
• Transversals, duality, and irrational rotation
• Homotopy of product systems and K-theory of Cuntz-Nica-Pimsner algebras
• A Dolbeault-Hilbert complex for a variety with isolated singular points