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The odd spectral localiser via asymptotic morphisms and quasi-projections

Yuezhao Li and Bram Mesland

Vol. 11 (2026), No. 2, 213–260
Abstract

We describe the index pairing between an odd K-theory class and an odd unbounded Kasparov module by a pair of quasi-projections, supported on a submodule obtained from a finite spectral truncation. We achieve this by pairing the K-theory class with an asymptotic morphism determined by the unbounded Kasparov module. We interpret the spectral localiser of Loring and Schulz-Baldes as an instance of such an index pairing.

Keywords
Kasparov theory, asymptotic morphisms, computational $K$-theory
Mathematical Subject Classification
Primary: 19K35, 46L80
Milestones
Received: 15 July 2025
Revised: 28 October 2025
Accepted: 28 November 2025
Published: 30 March 2026
Authors
Yuezhao Li
Mathematisch Instituut
Universiteit Leiden
Leiden
Netherlands
Bram Mesland
Mathematisch Instituut
Universiteit Leiden
Leiden
Netherlands