Noncommutative Topology and Prospects in Index Theory

TL;DR

This paper develops a local approach to index theory using noncommutative topology, introducing new tools like local Alexander-Spanier cohomology and local T*-theory to unify classical and noncommutative index theorems.

Contribution

It introduces local versions of cohomology, cyclic homology, and T*-theory, extending index theory to noncommutative topology and providing a unified framework for classical and noncommutative index theorems.

Findings

Development of local Alexander-Spanier cohomology and local cyclic homology.

Extension of T*-theory to noncommutative topology.

A three-stage index formula unifying classical and noncommutative cases.

Abstract

This article is a tribute to the memory of Professor Enzo Martinelli, with deep respect and reconesance. Nicolae Teleman. The index formula is a local statement made on global and local data; for this reason we introduce local Alexander - Spanier co-homology, local periodic cyclic homology, local Chern character and local $T^{\ast}$-theory. Index theory should be done: Case 1: for arbitrary rings, Case 2: for rings of functions over topo- logical manifolds. Case 1 produces general index theorems, as for example, over pseudo-manifolds. Case 2 gives a general treatment of classical and non- commutative index theorems. All existing index theorems belong to the second category. The tools of the theory would contain: local $T^{\ast}$ -theory, local peri- odic cyclic homology, local Chern character. These tools are extended to non- commutative topology. The index formula has three stages : Stage I is done in $T^{loc}\_{i}$-theory, Stage II is done in the local periodic cyclic homology and Stage III involves products of distributions, or restriction to the diagonal. For each stage there corresponds a topological index and an analytical index. The construction of $T^{\ast}$-theory involves the T-completion. It involves also the need to work with half integers; this should have important consequences.