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Simple Toroidal Vertex Algebras and Their Irreducible Modules

In this paper, we continue the study on toroidal vertex algebras initiated in \cite{LTW}, to study concrete toroidal vertex algebras associated to toroidal Lie algebra $L_{r}(\hat{\frak{g}})=\hat{\frak{g}}\otimes L_r$, where $\hat{\frak{g}}$ is an untwisted affine Lie algebra and $L_r=$\mathbb{C}[t_{1}^{\pm 1},\ldots,t_{r}^{\pm 1}]$. We first construct an $(r+1)$-toroidal vertex algebra $V(T,0)$ and show that the category of restricted $L_{r}(\hat{\frak{g}})$-modules is canonically isomorphic to that of $V(T,0)$-modules.Let $c$ denote the standard central element of $\hat{\frak{g}}$ and set $S_c=U(L_r(\mathbb{C}c))$. We furthermore study a distinguished subalgebra of $V(T,0)$, denoted by $V(S_c,0)$. We show that (graded) simple quotient toroidal vertex algebras of $V(S_c,0)$ are parametrized by a $\mathbb{Z}^r$-graded ring homomorphism $ψ:S_c\rightarrow L_r$ such that Im$ψ$ is a $\mathbb{Z}^r$-graded simple $S_c$-module. Denote by $L(ψ,0}$ the simple $(r+1)$-toroidal vertex algebra of $V(S_c,0)$ associated to $ψ$. We determine for which $ψ$, $L(ψ,0)$ is an integrable $L_{r}(\hat{\frak{g}})$-module and we then classify irreducible $L(ψ,0)$-modules for such a $ψ$. For our need, we also obtain various general results.