Cyclotomic level maps and associated varieties of simple affine vertex algebras

In this paper, we introduce and study two cyclotomic level maps defined respectively on the set of nilpotent orbits $\underset{‾}{\mathcal{N}}$ in a complex semi-simple Lie algebra $\mathfrak{g}$ and the set of conjugacy classes $\underset{‾}{W}$ in its Weyl group, with values in positive integers. We show that these maps are compatible under Lusztig’s map $\underset{‾}{W}\to \underset{‾}{\mathcal{N}}$, which is also the minimal reduction type map as shown by Yun. We also discuss their relationship with two-sided cells in affine Weyl groups. We use these maps to formulate a conjecture on the associated varieties of simple affine vertex algebras attached to $\mathfrak{g}$ at non-admissible integer levels, and provide some evidence for this conjecture.