$C_2$-Cofiniteness of Permutation Orbifolds I: Relative $C_1$ Descent

Abstract

We establish a relative $C_1$-cofiniteness criterion for $C_2$-cofiniteness of finite group orbifolds. For permutation actions on a simple, self contragredient, $C_2$-cofinite vertex operator algebra of CFT type, it suffices to check a single relation for a derivative of the conformal vector in the Virasoro vertex operator algebra. This reduces the problem to a calculation depending only on the central charge and tensor degree. An exact calculation then proves cofiniteness for a family of nonsolvable permutation orbifolds without restricting the central charge.