Document Type: Special Issue of BIMS in Honor of Professor Freydoon Shahidi
Let $G$ be a tamely ramified reductive $p$-adic group. We study distinction of a class of irreducible admissible representations of $G$ by the group of fixed points $H$ of an involution
of $G$. The representations correspond to $G$-conjugacy classes of pairs $(T,\phi)$, where $T$ is a tamely ramified maximal torus of $G$ and $\phi$ is a quasicharacter of $T$ whose restriction to the maximal pro-$p$-subgroup satisfies a regularity condition.
Under mild restrictions on the residual characteristic of $F$, we derive necessary conditions for $H$-distinction of a representation corresponding to $(T,\phi)$, expressed in terms of properties of $T$ and $\phi$ relative to the involution.
We prove that if an $H$-distinguished representation arises from a pair $(T,\phi)$ such that $T$ is stable under the involution and compact modulo $(T\cap H)Z$ (here, $Z$ is the centre of
$G$), then the representation is $H$-relatively supercuspidal.