Classifying relaxed highest-weight modules for admissible-level Bershadsky-Polyakov algebras

TL;DR

This paper classifies simple relaxed highest-weight modules with finite-dimensional weight spaces for Bershadsky-Polyakov algebras at admissible nonintegral levels, revealing their rationality and module structure properties relevant to conformal field theory.

Contribution

It extends the classification of modules for Bershadsky-Polyakov algebras to nonintegral admissible levels, showing rationality and the existence of nonsemisimple modules.

Findings

Bershadsky-Polyakov algebras at admissible nonintegral levels are rational in category O.

They admit nonsemisimple relaxed highest-weight modules unless a specific integer condition on the level holds.

The classification significantly generalizes previous highest-weight module classifications.

Abstract

The Bershadsky-Polyakov algebras are the minimal quantum hamiltonian reductions of the affine vertex algebras associated to $\mathfrak{sl}_3$ and their simple quotients have a long history of applications in conformal field theory and string theory. Their representation theories are therefore quite interesting. Here, we classify the simple relaxed highest-weight modules, with finite-dimensional weight spaces, for all admissible but nonintegral levels, significantly generalising the known highest-weight classifications [arxiv:1005.0185, arxiv:1910.13781]. In particular, we prove that the simple Bershadsky-Polyakov algebras with admissible nonintegral $\mathsf{k}$ are always rational in category $\mathscr{O}$, whilst they always admit nonsemisimple relaxed highest-weight modules unless $\mathsf{k}+\frac{3}{2} \in \mathbb{Z}_{\ge0}$.