Integral elements of Okubo algebra and the E8-lattice

Abstract

In this work we study the interplay between the Coxeter-Dickson $E_8$-order, the para-octonions, and the real Okubo algebra. We first explain why a usual rotation presentation of the order-three automorphism, although algebraically correct, does not preserve the classical integral orders. We then introduce an integral order-three automorphism and prove that its Petersson isotope is the compact real Okubo algebra. The four octonionic orders with lattices $C_8$, $A_2^4$, $D_4^2$, and $E_8$ are preserved by the new realisation of the Okubo product. In particular, the same Coxeter-Dickson $E_8$ lattice supports octonionic, para-octonionic, and Okubo integral structures, although the resulting multiplicative systems are not isomorphic.