The structure of the Kac-Wang-Yan algebra

TL;DR

This paper explores the structure of certain vertex algebras derived from the Kac-Wang-Yan algebra, revealing their classification as specific types of W-algebras and connecting these structures to invariant theory of classical groups.

Contribution

It establishes the isomorphism of specific vertex algebras with W-algebras of certain types, linking algebraic structures to invariant theory, and proves new conjectures for particular cases.

Findings

$ ext{V}_{n/2}$ and $ ext{V}_{-n}$ are W-algebras of specified types.

Invariant subalgebras under group actions are strongly finitely generated.

Proved the conjecture for $n=1$ regarding $ ext{V}_{-n+1/2}$.

Abstract

The Lie algebra $\mathcal{D}$ of regular differential operators on the circle has a universal central extension $\hat{\mathcal{D}}$. The invariant subalgebra $\hat{\mathcal{D}}^+$ under an involution preserving the principal gradation was introduced by Kac, Wang, and Yan. The vacuum $\hat{\mathcal{D}}^+$-module with central charge $c\in\mathbb{C}$, and its irreducible quotient $\mathcal{V}_c$, possess vertex algebra structures, and $\mathcal{V}_c$ has a nontrivial structure if and only if $c\in \frac{1}{2}\mathbb{Z}$. We show that for each integer $n>0$, $\mathcal{V}_{n/2}$ and $\mathcal{V}_{-n}$ are $\mathcal{W}$-algebras of types $\mathcal{W}(2,4,\dots,2n)$ and $\mathcal{W}(2,4,\dots, 2n^2+4n)$, respectively. These results are formal consequences of Weyl's first and second fundamental theorems of invariant theory for the orthogonal group $\text{O}(n)$ and the symplectic group $\text{Sp}(2n)$, respectively. Based on Sergeev's theorems on the invariant theory of $\text{Osp}(1,2n)$ we conjecture that $\mathcal{V}_{-n + 1/2}$ is of type $\mathcal{W}(2,4,\dots, 4n^2+8n+2)$, and we prove this for $n=1$. As an application, we show that invariant subalgebras of $\beta\gamma$-systems and free fermion algebras under arbitrary reductive group actions are strongly finitely generated.