Theta distinguished representations, inflation and the symmetric square L-function

Abstract

Let $\Pi_0$ be a representation of a group $H$. We say that a representation $\tau$ is $(H,\Pi_0)$-distinguished, if it is a quotient of $\Pi_0$. It is natural to ask whether this notion "inflates" to larger groups, in the sense that a representation $\mathrm{I}(\tau)$ induced from $\tau$ and $H$ to a group $G$, is $(G,\Pi)$-distinguished. We study representations distinguished by theta representations: $H=GL_n$, $\Pi_0$ is a pair of the exceptional representations of Kazhdan and Patterson, $G=GSpin_{2n+1}$ and $\Pi$ is a pair of the small representations of Bump, Friedberg and Ginzburg. We prove a Rodier-type hereditary property: a tempered representation $\tau$ is distinguished if and only if $\mathrm{I}(\tau)$ is distinguished, and the multiplicity in each model is the same. If $\tau$ is supercuspidal and distinguished, we prove that the Langlands quotient of $\mathrm{I}(\tau)$ is distinguished. As a corollary, we characterize supercuspidal distinguished representations, in terms of the pole of the local symmetric square $L$-function at $s=0$.