DISCRETE DECOMPOSABLE BRANCHING LAWS AND PROPER MOMENTUM MAPS
Abstract
Suppose an irreducible unitary representation π of a Lie group G is obtained as a geometric quantization of a coadjoint orbit in the Kirillov–Kostant–Duflo orbit philosophy. Let H be a closed subgroup of G, and we compare the following two conditions.
(1) The restriction π|H is discretely decomposable in the sense of Kobayashi.
(2) The momentum map is proper.
In this article, we prove that (1) is equivalent to (2) when π is any holomorphic discrete series representation of scalar type of a semisimple Lie group G and (G, H) is any symmetric pair.