Normed Fiber Functors

Abstract

By Goldman-Iwahori, the Bruhat-Tits building of the general linear group ${\mathrm{GL}}_n$ over a local field $\ell$ can be described as the set of non-archimedean norms on ${\ell }^n$. Via a Tannakian formalism, we generalize this picture to a description of the Bruhat-Tits building of an unramified reductive group $G$ over $\ell$ as the set of norms on the standard fiber functor of a special parahoric integral model of $G$. We also give a moduli-theoretic description of the parahoric group scheme associated to a point of the building as the group scheme of tensor automorphisms of the lattice chains defined by the corresponding norm.