On dual groups of symmetric varieties and distinguished representations of $p$-adic groups

Abstract: Let $X=H\backslash G$ be a symmetric variety over a $p$-adic field. Assume $G$ is split. Let $\widehat{G}$ be the Langlands dual group of $G$. There is a complex group $\widehat{G}_X$ whose root datum is naturally constructed from that of $\widehat{G}$. In this paper, we construct a homomorphism $\widehat{\varphi}_X:\widehat{G}_X\times\operatorname{SL}_2(\mathbb{C})\to \widehat{G}$ naturally and somewhat explicitly, and make a few conjectures on how $\widehat{\varphi}_X$ is related to $H$-distinguished representations of $G$. We will also show that the local Langlands parameter of the trivial representation of $G$ factors through $\widehat{\varphi}_X$ for any symmetric variety $X=H\backslash G$. Our group $\widehat{G}_X$ is different from the dual group by Sakellaridis-Venkatesh. However, we will show that our conjectures are consistent with various known examples and conjectures, especially in the framework of the theory of Kato-Takano on relative cuspidality and relative square integrability.