Twisted K-theory constructions in the case of a decomposable Dixmier-Douady class II: Topological and equivariant models

TL;DR

This paper develops models for twisted K-theory on product spaces with decomposable Dixmier-Douady classes, providing explicit constructions and analyzing equivariant cases using superconnection formalism and Lie groupoid theory.

Contribution

It offers concrete realizations of twisted K-theory elements and gerbes for decomposable classes, extending the understanding of topological and equivariant twisted K-theory.

Findings

Constructed explicit gerbe models for decomposable classes

Realized twisted K-theory elements via supercharge sections

Analyzed equivariant twisted K-theory using Lie groupoid theory

Abstract

This is a study of twisted K-theory on a product space $T \times M$. The twisting comes from a decomposable cup product class which applies the 1-cohomology of $T$ and the 2-cohomology of $M$. In the case of a topological product, we give a concrete realization for the gerbe associated to a cup product characteristic class and use this to realize twisted $K^1$-theory elements in terms of supercharge sections in a Fredholm bundle. The nontriviality of this construction is proved. Equivariant twisted K-theory and gerbes are studied in the product case as well. This part applies Lie groupoid theory. Superconnection formalism is used to provide a construction for characteristic polynomials which are used to extract information from the twisted K-theory classes.