Fixed point formula and loop group actions

Abstract

The main goal of this paper is to obtain a formula for the T-equivariant Riemann-Roch number of certain G-spaces which are the finite dimensional models of certain infinite dimensional spaces with Hamiltonian LG-actions, here T is a maximal torus of the semi-simple Lie group G. Unlike its finite dimensional cousin, the formula obtained here only needs to valuate on a finite subgroup of T depending on the 'level' of the LG-action and the dual Coxeter number of G, due to a fundamental cancelation. If the fixed-point sets of elements of the finite subgroup do not intersect the compactification locus used in constructing the finite dimensional model, the fixed point formula has a particularly simple form, which will be shown for the case of Verlinde formula. This paper was written in early 1997 and had limited circulation, before I left academia. The version here has a computer time-stamp 6/10/97. I have been urged by former colleaques to archive this article together with its sequels on the net.