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 $L_r(\widehat{\mathfrak{g}})=\widehat{\mathfrak{g}}\otimes L_r$, where $\widehat{\mathfrak{g}}$ is an untwisted affine Lie algebra and $L_r=$$\mathbb{C}$[t_{1}^{\pm 1},\ldots,t_{r}^{\pm 1}]$\mathrm{.}Wefirstconstructan$(r+1)$-toroidalvertexalgebra$V(T,0)$ and show that the category of restricted $L_r(\widehat{\mathfrak{g}})$-modules is canonically isomorphic to that of $V(T,0)$-modules.Let $c$ denote the standard central element of $\widehat{\mathfrak{g}}$ and set $S_c=U(L_r(\mathbb{C}c))$. We furthermore study a distinguished subalgebra of $V(T,0)$, denoted by $V(S_c,0)$. We show that (graded) simple quotient toroidal vertex algebras of $V(S_c,0)$ are parametrized by a ${\mathbb{Z}}^r$-graded ring homomorphism $\psi:S_c\rightarrow L_r$suchthatIm$\psi$isa$$\mathbb{Z}$^r$-gradedsimple$S_c$-module. Denote by L(\psi,0} the simple $(r+1)$-toroidal vertex algebra of $V(S_c,0)$ associated to $\psi$. We determine for which $\psi$, $L(\psi ,0)$ is an integrable $L_r(\widehat{\mathfrak{g}})$-module and we then classify irreducible $L(\psi ,0)$-modules for such a $\psi$. For our need, we also obtain various general results.