Quantization of Hamiltonian loop group spaces

TL;DR

This paper establishes a Fredholm property for spin-c Dirac operators on certain non-compact manifolds and applies it to Hamiltonian loop group spaces, linking index pairings to positive energy representations.

Contribution

It proves a Fredholm property for Dirac operators on non-compact manifolds with group actions and connects index pairings in Hamiltonian loop group spaces to representation theory.

Findings

Fredholm property for spin-c Dirac operators on non-compact manifolds.

Index pairing yields elements in the representation ring of a maximal torus.

Resulting elements exhibit antisymmetry under the affine Weyl group.

Abstract

We prove a Fredholm property for spin-c Dirac operators $\mathsf{D}$ on non-compact manifolds satisfying a certain condition with respect to the action of a semi-direct product group $K\ltimes \Gamma$, with $K$ compact and $\Gamma$ discrete. We apply this result to an example coming from the theory of Hamiltonian loop group spaces. In this context we prove that a certain index pairing $[\mathcal{X}] \cap [\mathsf{D}]$ yields an element of the formal completion $R^{-\infty}(T)$ of the representation ring of a maximal torus $T \subset G$; the resulting element has an additional antisymmetry property under the action of the affine Weyl group, indicating $[\mathcal{X}] \cap [\mathsf{D}]$ corresponds to an element of the ring of projective positive energy representations of the loop group.