A decomposition of the Brauer-Picard group of the representation category of a finite group

TL;DR

This paper develops a method to compute the Brauer-Picard group of the representation category of a finite group, revealing a decomposition that relates to Lie group structures and applications in topological quantum field theory.

Contribution

It introduces a decomposition approach for the Brauer-Picard group of the representation category of a finite group, connecting it to Bruhat decomposition and Lie groups over finite fields.

Findings

Decomposition of the Brauer-Picard group into generators under cohomological conditions

Reduction to Bruhat decomposition for elementary abelian groups

Applications to symmetries and defects in 3d-TQFT

Abstract

We present an approach of calculating the group of braided autoequivalences of the category of representations of the Drinfeld double of a finite dimensional Hopf algebra $H$ and thus the Brauer-Picard group of $H$-$\mathrm{mod}$. We consider two natural subgroups and a subset as candidates for generators. In this article $H$ is the group algebra of a finite group $G$. As our main result we prove that any element of the Brauer-Picard group, fulfilling an additional cohomological condition, decomposes into an ordered product of our candidates. For elementary abelian groups $G$ our decomposition reduces to the Bruhat decomposition of the Brauer-Picard group, which is in this case a Lie group over a finite field. Our results are motivated by and have applications to symmetries and defects in $3d$-TQFT and group extensions of fusion categories.