Functoriality properties of the dual group

Abstract

Let $G$ be a connected reductive group. In a previous paper, arxiv:1702.08264, is was shown that the dual group $G_X^{\vee }$ attached to a $G$-variety $X$ 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 canonical homomorphism $G_Y^{\vee }\to G_X^{\vee }$ which is compatible with the homomorphisms to $G^{\vee }$.

arXiv commentv1:14 pages; v2: 16 pages, changed Rem. 2.3, Rem. 2.9, proof of Thm. 3.2; v3: 2 typos corrected