Hopf algebroids, Hopf categories and their Galois theories

TL;DR

This paper explores the relationship between Hopf algebroids and Hopf categories, establishing a connection via topological structures and Galois theories using algebraic geometry and spectral theory.

Contribution

It introduces the concept of topological Hopf categories and links finitely-generated projective Hopf algebroids over commutative C*-algebras to these categories, along with their Galois theories.

Findings

Finitely-generated projective Hopf algebroids over C*-algebras correspond to topological Hopf categories.

The Galois theories of these structures are closely related.

Methods of algebraic geometry and spectral theory are used to establish these connections.

Abstract

Hopf algebroids are generalization of Hopf algebras over non-commutative base rings. It consists of a left- and a right-bialgebroid structure related by a map called the antipode. However, if the base ring of a Hopf algebroid is commutative one does not necessarily have a Hopf algebra. Meanwhile, a Hopf category is the categorification of a Hopf algebra. It consists of a category enriched over a braided monoidal category such that every hom-set carries a coalgebra structure together with an antipode functor. In this article, we will introduce the notion of a topological Hopf category$-$ a small category whose set of objects carries a topology and whose categorical structure maps are sufficiently continuous. The main result of this paper is to describe the relation between finitely-generated projective Hopf algebroids over commutative unital $C^{*}-$algebras and topological coupled Hopf categories of finite-type whose space of objects is compact and Hausdorff. We will accomplish this by using methods of algebraic geometry and spectral theory. Lastly, we will show that not only the two objects are tightly related, but so are their respective Galois theories.