On some vertex algebras related to $V_{-1}(\frak{sl} (n) )$ and their characters

TL;DR

This paper explores vertex algebras related to $V_{-1}(\mathfrak{sl}(n))$, describing their structure, modules, and characters, and conjectures their quasi-lisse property with evidence from modularity and differential equations.

Contribution

It introduces new vertex algebras connected to $V_{-1}(\mathfrak{sl}(n))$, describes their modules and characters, and proposes their quasi-lisse nature supported by modularity evidence.

Findings

The algebra $\mathcal U$ is isomorphic to a coset vertex algebra.

$V_{-1}(\mathfrak{sl}(n))$ admits exactly $n$ irreducible modules.

The supercharacter of $\mathcal U$ is quasi-modular of weight one.

Abstract

We consider several vertex operator (super)algebras closely related to $V_{-1}(\frak{sl} (n) )$, $n \ge 3$ : (a) the parafermionic subalgebra $K(\frak{sl}(n),-1)$ for which we completely describe its inner structure, (b) the vacuum algebra $\Omega (V_{-1}(\frak{sl} (n) ) )$, and (c) an infinite extension $\mathcal U$ of $V_{-1}(\frak{sl} (n) )$ constructed by combining certain irreducible ordinary modules with integral weights. It turns out that $\mathcal U$ is isomorphic to the coset vertex algebra $\frak{psl}(n|n) _1 / \frak{sl}(n)_1$, $n \ge 3$. We show that $V_{-1}(\frak{sl}(n))$ admits precisely $n$ ordinary irreducible modules, up to isomorphism. This leads to the conjecture that ${\mathcal U}$ is {\em quasi-lisse}. We present evidence in support of this conjecture: we prove that the (super)character of $\mathcal U$ is quasi-modular of weight one by virtue of being the constant term of a meromorphic Jacobi form of index zero. Explicit formulas and MLDE for characters and supercharacters are given for $\frak{g}=\frak{sl}(3)$ and outlined for general $n$. We present a conjectural family of 2nd order MLDEs for characters of vertex algebras $\frak{psl}(n|n) _1$, $n \geq 2$. We finish with a theorem pertaining to characters of $\frak{psl}(n|n)_1$ and $\mathcal U$-modules.