  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.
