Functoriality Properties of the Dual Group

Abstract

Let $G$ be a connected reductive group. Previously, it was shown that for any $G$-variety $X$ one can define the dual group $G_X^{\vee }$ which admits a natural homomorphism with finite kernel to the Langlands dual group $G^{\vee }$ of $G$. Here, we prove that the dual group is functorial in the following sense: if there is a dominant $G$-morphism $X\to Y$ or an injective $G$-morphism $Y\to X$ then there is a unique homomorphism with finite kernel $G_Y^{\vee }\to G_X^{\vee }$ which is compatible with the homomorphisms to $G^{\vee }$.