A Localization Argument for Characters of Reductive Lie Groups

This article provides a geometric bridge between two entirely different character formulas for reductive Lie groups and answers the question posed by W.Schmid in [Sch]. A corresponding problem in the compact group setting was solved by N.Berline, E.Getzler and M.Vergne in [BGV] by an application of the theory of equivariant forms and particularly the fixed point integral localization formula. This article (besides its representation-theoretical significance) provides a whole family of examples where it is possible to localize integrals to fixed points with respect to an action of a NONcompact group. Moreover, a localization argument given here is not specific to the particular setting considered in this article and can be extended to a more general situation. There is a broadly accessible article [L] which explains how the argument works in the SL(2,R) case, where the key ideas are not obstructed by technical details and where it becomes clear how it extends to the general case.