Algebraic quantum groupoids - An example

TL;DR

This paper provides an in-depth exposition of a specific example of algebraic quantum groupoids constructed from separability idempotents, illustrating the general theory and duality in this mathematical framework.

Contribution

It presents a detailed example of algebraic quantum groupoids and their duals, clarifying the structure and properties within the theory of weak multiplier Hopf algebras.

Findings

Construction of a unimodular algebraic quantum groupoid from separability idempotents

Explicit duality between algebraic quantum groupoids and their duals

Comprehensive exposition of the theory with illustrative examples

Abstract

Let $B$ and $C$ be non-degenerate idempotent algebras and assume that $E$ is a regular separability idempotent in $M(B\otimes C)$. Define $A=C\otimes B$ and $\Delta:A\to M(A\otimes A)$ by $\Delta(c\otimes b)=c\otimes E\otimes b$. The pair $(A,\Delta)$ is a weak multiplier Hopf algebra. Because we assume that $E$ is regular, it is a regular weak multiplier Hopf algebra. There is a faithful left integral on $(A,\Delta)$ that is also right invariant. Therefore, we call $(A,\Delta)$ a unimodular algebraic quantum groupoid. By the general theory, the dual $(\widehat A,\widehat \Delta)$ can be constructed and it is again an algebraic quantum groupoid. In this paper, we treat this algebraic quantum groupoid and its dual in great detail. The main purpose is to illustrate various aspects of the general theory. For this reason, we will also recall the basic notions and results of separability idempotents and weak multiplier Hopf algebras with integrals. The paper is to be considered as an expository note.