How does the restriction of representations change under translations? A story for the general linear groups and the unitary groups

Toshiyuki Kobayashi, Birgit Speh

Published 2025-02-12Version 1

We present a new approach to symmetry breaking for pairs of real forms of $(GL(n, \mathbb{C}), GL(n-1, \mathbb{C}))$. While translation functors are a useful tool for studying a family of representations of a single reductive group $G$, when applied to a pair of groups $G \supset G'$,translation functors can significantly alter the nature of symmetry breaking between the representations of $G$ and $G'$, even within the same Weyl chamber of the direct product group $G \times G'$. We introduce the concept of \lq\lq{fences for the interlacing pattern}\rq\rq,which provides a refinement of the usual notion of \lq\lq{walls for Weyl chambers}\rq\rq. We then present a theorem that states that multiplicity is constant unless these \lq\lq{fences}\rq\rq\ are crossed. This general theorem is illustrated with examples of both tempered and non-tempered representations. Additionally,we provide a new non-vanishing theorem of period integrals for pairs of reductive symmetric spaces,which is further strengthened through this approach.