Homological aspects of branching laws

Abstract

In this mostly expository article, we consider certain homological aspects of branching laws for representations of a group restricted to its subgroups in the context of $p$-adic groups. We follow our earlier paper, ICM 2018 proceedings, updating it with some more recent works. In particular, following Chan and Chan-Savin, see many of their papers listed in the bibliography, we have emphasized in this work that the restriction of a (generic) representation $\pi$ of a group $G$ to a closed subgroup $H$ (most of the paper is written in the context of GGP) turns out to be a projective representation on most Bernstein blocks of the category of smooth representations of $H$. Further, once $\pi|_H$ is a projective module in a particular Bernstein block, it has a simple structure.