A relative Langlands dual realization of $T^*(G/K)$ and derived Satake

Abstract

We show that the cotangent bundle $T^*(G/K)$ of a quasi-split symmetric space $G/K$ is isomorphic to the dual variety of the loop symmetric space for the Langlands dual group, providing instances of the relative Langlands duality for non-split groups. Then we establish a Langlands dual description of equivariant coherent sheaves on $T^*(G/K)$ in terms of constructible sheaves on the loop symmetric spaces, generalizing the derived Satake equivalence for reductive groups to quasi-split symmetric spaces. To this end, we prove the derived Satake equivalence for the twisted affine Grassmannians, study ring objects arising from loop symmetric spaces, and explore the formality and fully-faithfulness properties of $!$-pure objects. We deduce a version of Bezrukavnikov equivalence for quasi-split symmetric spaces and make connections to the geometric Langlands on the twistor $\mathbb P^1$.