Ising vectors in the vertex operator algebra $V_Λ^+$ associated with the Leech lattice $Λ$

Abstract

In this article, we study the Ising vectors in the vertex operator algebra $V_Λ^+$ associated with the Leech lattice $Λ$. The main result is a characterization of the Ising vectors in $V_Λ^+$. We show that for any Ising vector $e$ in $V_Λ^+$, there is a sublattice $E\cong \sqrt{2}E_8$ of $Λ$ such that $e\in V_E^+$. Some properties about their corresponding $τ$-involutions in the moonshine vertex operator algebra $V^\natural$ are also discussed. We show that there is no Ising vector of $σ$-type in $V^\natural$. Moreover, we compute the centralizer $C_{\aut V^\natural}(z, τ_e)$ for any Ising vector $e\in V_Λ^+$, where $z$ is a 2B element in $\aut V^\natural$ which fixes $V_Λ^+$. Based on this result, we also obtain an explanation for the 1A case of an observation by Glauberman-Norton (2001), which describes some mysterious relations between the centralizer of $z$ and some 2A elements commuting $z$ in the Monster and the Weyl groups of certain sublattices of the root lattice of type $E_8$ .