Higher level twisted Zhu algebras (1105.0108v1)

Abstract: The study of twisted representations of graded vertex algebras is important for understanding orbifold models in conformal field theory. In this paper we consider the general set-up of a vertex algebra $V$, graded by $\G/\Z$ for some subgroup $\G$ of $\R$ containing $\Z$, and with a Hamiltonian operator $H$ having real (but not necessarily integer) eigenvalues. We construct the directed system of twisted level $p$ Zhu algebras $\zhu_{p, \G}(V)$, and we prove the following theorems: For each $p$ there is a bijection between the irreducible $\zhu_{p, \G}(V)$-modules and the irreducible $\G$-twisted positive energy $V$-modules, and $V$ is $(\G, H)$-rational if and only if all its Zhu algebras $\zhu_{p, \G}(V)$ are finite dimensional and semisimple. The main novelty is the removal of the assumption of integer eigenvalues for $H$. We provide an explicit description of the level $p$ Zhu algebras of a universal enveloping vertex algebra, in particular of the Virasoro vertex algebra $\vir^c$ and the universal affine Kac-Moody vertex algebra $V^k(\g)$ at non-critical level. We also compute the inverse limits of these directed systems of algebras.