Klein Four subgroups of Lie Algebra Automorphisms

Abstract

By calculating the symmetric subgroups $\Aut(\fru_0)^θ$ and their involution classes, we classify the Klein four subgroups $Γ$ of $\Aut(\fru_0)$ for each compact simple Lie algebra $\fru_0$ up to conjugation. This leads to a new approach of classification of semisimple symmetric pairs and $\bbZ_2\times \bbZ_2$-symmetric spaces. We also determine the fixed point subgroup $\Aut(\fru_0)^Γ$.

19 pages