For a semisimple Lie group satisfying the equal-rank condition, the most basic family of unitary irreducible representations is the discrete series found by Harish-Chandra. In our work here we study some of the branching laws for discrete series when restricted to a subgroup of the same type by combining classical results with recent work of Kobayashi; in particular, we prove discrete decomposability under Harish-Chandra’s condition of cusp form on the reproducing kernel. We show a relation between discrete decomposability and representing certain intertwining operators in terms of differential operators.
"Branching problems in reproducing kernel spaces." Duke Math. J. 169 (18) 3477 - 3537, 1 December 2020. https://doi.org/10.1215/00127094-2020-0032