English

Fusion Categories Associated to Subfactors with Index $3+\sqrt{5}$

Operator Algebras 2016-12-22 v1 Quantum Algebra

Abstract

We classify fusion categories which are Morita equivalent to even parts of subfactors with index 3+53+\sqrt{5} , and module categories over these fusion categories. For the fusion category C\mathcal{C} which is the even part of the self-dual 3Z/2Z×Z/2Z3^{\mathbb{Z}/2\mathbb{Z} \times \mathbb{Z}/2\mathbb{Z} } subfactor, we show that there are 3030 simple module categories over C \mathcal{C}; there are no other fusion categories in the Morita equivalence class; and the order of the Brauer-Picard group is 360360. The proof proceeds indirectly by first describing the Brauer-Picard groupoid of a Z/3Z \mathbb{Z}/3\mathbb{Z} -equivariantization CZ/3Z\mathcal{C}^{\mathbb{Z}/3\mathbb{Z} } (which is the even part of the 44424442 subfactor). We show that that there are exactly three other fusion categories in the Morita equivalence class of CZ/3Z\mathcal{C}^{\mathbb{Z}/3\mathbb{Z} } , which are all Z/3Z \mathbb{Z}/3\mathbb{Z} -graded extensions of C\mathcal{C} . Each of these fusion categories admits 2020 simple module categories, and their Brauer-Picard group is S3\mathcal{S}_3 . We also show that there are exactly five fusion categories in the Morita equivalence class of the even parts of the 3Z/4Z3^{\mathbb{Z}/4\mathbb{Z} } subfactor; each admits 77 simple module categories; and the Brauer-Picard group is Z/2Z\mathbb{Z}/2\mathbb{Z} .

Keywords

Cite

@article{arxiv.1612.07185,
  title  = {Fusion Categories Associated to Subfactors with Index $3+\sqrt{5}$},
  author = {Pinhas Grossman},
  journal= {arXiv preprint arXiv:1612.07185},
  year   = {2016}
}