Lattice vertex algebras of type ADE over fields of prime characteristic and their representations
We study lattice vertex algebras of type ADE over an algebraically closed field $\mathbb{F}$ of prime characteristic $p>2$ and their representations. Let $L$ be a root lattice of type ADE, and $G_{L}$ the Gram matrix of $L$. When $\det G_{L}\not \equiv 0\pmod{p}$, we establish an isomorphism between the lattice vertex algebra $V_{L,\mathbb{F}}$ and the level-one simple affine vertex algebra of the same type. Via this isomorphism, we classify the irreducible $\mathbb{N}$-graded modules of $V_{L,\mathbb{F}}$ viewed as an $\mathbb{N}$-graded vertex algebra. We also consider the case where $L$ is of type $A_n$ with $\det G_L=n+1\equiv 0\pmod{p}$. We show that $V_{L,\mathbb{F}}$ is not simple and determine the simple $\mathbb{N}$-graded quotient of $V_{L,\mathbb{F}}$. Furthermore, when $n+1=ap$ for some $a\in \mathbb{Z}_+$ with $\gcd(a,p)=1$, we give the classification of the irreducible $\mathbb{N}$-graded modules for the simple quotient of $V_{L,\mathbb{F}}$.