Trace Formulas in Noncommutative Geometry

TL;DR

This thesis develops new trace formulas and operator integral techniques in noncommutative geometry, including asymptotic expansions, noncommutative Taylor formulas, and applications to spectral triples and index theory.

Contribution

It introduces a functional calculus for abstract pseudodifferential operators and generalizes multiple operator integrals, providing new tools and formulas in noncommutative geometry.

Findings

Derived asymptotic heat trace expansions using operator integration.

Provided a noncommutative Taylor formula for pseudodifferential operators.

Established Dixmier trace formulas for spectral triples and geometric operators.

Abstract

Trace formulas appear in many forms in noncommutative geometry (NCG). In the first part of this thesis, we obtain results for asymptotic expansions of trace formulas like heat trace expansions by adapting the theory of Multiple Operator Integration to NCG. More broadly, this construction provides a natural language for operator integrals in NCG, which systematises and simplifies operator integral arguments throughout the literature. Towards this end, we construct a functional calculus for abstract pseudodifferential operators and generalise Peller's construction of multiple operator integrals to this abstract pseudodifferential calculus. In the process, we obtain a noncommutative Taylor formula. In the second part of this thesis, we shift our attention to Dixmier trace formulas. First, we provide an approximation of the noncommutative integral for spectrally truncated spectral triples in the Connes--Van Suijlekom paradigm of operator system spectral triples. Our approximation has a close link to Quantum Ergodicity, which we will use to state an NCG analogue of the fundamental result that ergodic geodesic flow implies quantum ergodicity. Furthermore, we provide a Szeg\H{o} limit theorem in NCG. Next, we provide a Dixmier trace formula for the density of states, a measure originating in solid state physics that can be associated with an operator on a geometric space. We first provide this formula in the setting of discrete metric spaces, and then in the setting of manifolds of bounded geometry. The latter leads to a Dixmier trace formula for Roe's index on open manifolds.