Principal Series Representations for some Infinite Dimensional Lie Groups

Joseph A.Wolf
(University of California, Berkeley)

Abstract: In semisimple Lie group theory, the most accessible unitary representations are the principal series representations. These are the representations unitarily induced from representations of minimal parabolic subgroups. Now let G be an infinite dimensional simple direct limit Lie group, for example SL(∞,R), Sp(17,∞) or SO(∞,∞), say G = lim Gn. If a minimal parabolic subgroup P in G is the limit of minimal parabolics Pn in the Gn, and if one is careful, then some principal series representations of G can be constructed as direct limits of principal series representations of the Gn. This sidesteps the problems caused by lack of Haar measure on G. But most (in some sense almost all) parabolics in G are more complicated, and one needs a substitute for Haar measure. I'll describe the structure of minimal parabolics in general and the use of amenability to carry out the induction step for construction of principal series representations.