Topological Aspects of the Equivariant Index Theory of Infinite-Dimensional LT-Manifolds

TL;DR

This paper develops a topological framework for the equivariant index theory of infinite-dimensional manifolds with loop group actions, introducing new KK-theoretic tools and extending classical concepts to infinite dimensions.

Contribution

It introduces $ kk$-theory for infinite-dimensional manifolds and formulates an infinite-dimensional Poincaré duality and assembly map for proper $LT$-spaces, extending index theory.

Findings

Formulated an infinite-dimensional version of the $KK$-theoretical Poincaré duality.

Developed a new $ kk$-theory framework for proper $LT$-spaces.

Proposed an alternative definition of crossed products using generalized fixed-point algebras.

Abstract

Let $T$ be the circle group and let $LT$ be its loop group. We formulate and investigate several topological aspects of the $LT$-equivariant index theory for proper $LT$-spaces, where proper $LT$-spaces are infinite-dimensional manifolds equipped with "proper cocompact" $LT$-actions. Concretely, we introduce "$\mathcal{R}KK$-theory for infinite-dimensional manifolds", and by using it, we formulate an infinite-dimensional version of the $KK$-theoretical Poincar\'e duality homomorphism, and an infinite-dimensional version of the $\mathcal{R}KK$-theory counterpart of the assembly map, for proper $LT$-spaces. The left hand side of the Poincar\'e duality homomorphism is formulated by the "$C^*$-algebra of a Hilbert manifold" introduced by Guoliang Yu. Thus, the result of this paper suggests that this construction carries some topological information of Hilbert manifolds. In order to formulate the assembly map in a classical way, we need crossed products, which require an invariant measure of a group. However, there is an alternative formula to define them using generalized fixed-point algebras. We will adopt it as the definition of "crossed products by $LT$".