Constructing modular categories from orbifold data

TL;DR

This paper constructs new modular categories from orbifold data in existing categories, unifying different algebraic constructions and providing explicit examples related to Frobenius algebras and spherical fusion categories.

Contribution

It introduces a method to derive modular categories from orbifold data, linking Frobenius algebras and Drinfeld centres within a unified framework.

Findings

The category $$ is a modular fusion category.

In case (i), $$ is equivalent to local modules of $A$.

In case (ii), $$ is equivalent to the Drinfeld centre of $$.

Abstract

In Carqueville et al., arXiv:1809.01483, the notion of an orbifold datum $\mathbb{A}$ in a modular fusion category $\mathcal{C}$ was introduced as part of a generalised orbifold construction for Reshetikhin-Turaev TQFTs. In this paper, given a simple orbifold datum $\mathbb{A}$ in $\mathcal{C}$, we introduce a ribbon category $\mathcal{C}_{\mathbb{A}}$ and show that it is again a modular fusion category. The definition of $\mathcal{C}_{\mathbb{A}}$ is motivated by properties of Wilson lines in the generalised orbifold. We analyse two examples in detail: (i) when $\mathbb{A}$ is given by a simple commutative $\Delta$-separable Frobenius algebra $A$ in $\mathcal{C}$; (ii) when $\mathbb{A}$ is an orbifold datum in $\mathcal{C} = \operatorname{Vect}$, built from a spherical fusion category $\mathcal{S}$. We show that in case (i), $\mathcal{C}_{\mathbb{A}}$ is ribbon-equivalent to the category of local modules of $A$, and in case (ii), to the Drinfeld centre of $\mathcal{S}$. The category $\mathcal{C}_{\mathbb{A}}$ thus unifies these two constructions into a single algebraic setting.