Fusion in the Extended Verlinde Algebra

Abstract

In this paper we study modular $G$-equivariant fusion categories and their extended Verlinde algebras. We dicuss settings in which fusion rules are diagonalizable. In particular, when $G = \mathbb{Z}_{2}$ we generalize the Verlinde formula. We discuss an important example at length: the type $D_{2m+2}$ quantum subgroup of the semisimple representations of $\mathcal{U}_{q}(\mathfrak{sl}_{2})$.