Fibre functors of finite dimensional comodules

Abstract

Let A be a commutative Hopf algebra over a field k; the k-valued fibre functors on the category of finite dimensional A-comodules correspond to Spec(A)-torsors over k as was shown by Saavedra Rivano and Deligne-Milne. We prove a non-commutative version of this result by using methods developed in a previous paper [5] for the case of finite Hopf algebras over a commutative ring. We also exhibit right adjoints for fibre functors under the assumption that the antipode is bijective.