Analytic Kasparov product for non-separable C$^*$-algebras

Abstract

We develop an analytic framework for the explicit construction of Kasparov products on uncountably generated Hilbert modules over non-separable C$^*$-algebras by extending the classical Kasparov bimodule picture. In particular, this yields a well-defined functor from the category of general C$^*$-algebras whose restriction to separable C$^*$-algebras coincides with classical KK-theory and which satisfies several properties expected of non-separable KK-theory. A key idea of the extension is to replace a single Fredholm operator on a Kasparov bimodule with a net and to encode the directed system of separable C$^*$-subalgebras. We also introduce the notion of freely complementable Hilbert modules and develop cropping techniques to extend Kasparov's technical theorem beyond the countably generated setting. It naturally gives rise to a sufficiently broad class of C$^*$-algebras that provides a non-commutative analogue of paracompactness and includes all $σ$-unital algebras.