Symmetry breaking for $\operatorname{PGL}(2)$ over non-archimedean local fields

Corina Ciobotaru, Jan Frahm

Published 2023-09-26Version 1

For a quadratic extension $\mathbb{E}/\mathbb{F}$ of non-archimedean local fields we construct explicit holomorphic families of intertwining operators between principal series representations of $\operatorname{PGL}(2,\mathbb{E})$ and $\operatorname{PGL}(2,\mathbb{F})$, also referred to as symmetry breaking operators. These families are given in terms of their distribution kernels which can be viewed as distributions on $\mathbb{E}$ depending holomorphically on the principal series parameters. For all such parameters we determine the support of these distributions, and we study their mapping properties. This leads to a classification of all intertwining operators between principal series representations, not necessarily irreducible. As an application, we show that every Steinberg representation of $\operatorname{PGL}(2,\mathbb{E})$ contains a Steinberg representation of $\operatorname{PGL}(2,\mathbb{F})$ as a direct summand of Hilbert spaces.