Vol. 296, No. 2, 2018

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ISSN: 0030-8730
Congruence subgroups and super-modular categories

Parsa Bonderson, Eric C. Rowell, Zhenghan Wang and Qing Zhang

Vol. 296 (2018), No. 2, 257–270
Abstract

A super-modular category is a unitary premodular category with Müger center equivalent to the symmetric unitary category of super-vector spaces. Super-modular categories are important alternatives to modular categories as any unitary premodular category is the equivariantization of a either a modular or super-modular category. Physically, super-modular categories describe universal properties of quasiparticles in fermionic topological phases of matter. In general one does not have a representation of the modular group SL(2, ) associated to a super-modular category, but it is possible to obtain a representation of the (index 3) θ-subgroup: Γθ < SL(2, ). We study the image of this representation and conjecture a super-modular analogue of the Ng–Schauenburg congruence subgroup theorem for modular categories, namely that the kernel of the Γθ representation is a congruence subgroup. We prove this conjecture for any super-modular category that is a subcategory of modular category of twice its dimension, i.e., admitting a minimal modular extension. Conjecturally, every super-modular category admits (precisely 16) minimal modular extensions and our conjecture would be a consequence.

Keywords
spin mapping class group, super-modular category, fermionic modular category
Mathematical Subject Classification 2010
Primary: 18D10
Milestones
Received: 15 April 2017
Accepted: 27 January 2018
Published: 16 July 2018
Authors
Parsa Bonderson
Microsoft Research-Station Q
University of California,
Santa Barbara, CA
United States
Eric C. Rowell
Department of Mathematics
Texas A&M University
College Station, TX
United States
Zhenghan Wang
Microsoft Research-Station Q
University of California,
Santa Barbara, CA
United States
Qing Zhang
Department of Mathematics
Texas A&M University
College Station, TX
United States