Discovering Real Lie Subalgebras of e6 using Cartan Decompositions

TL;DR

This paper introduces a method combining Cartan decompositions and the Killing form to identify real Lie subalgebras of e6, demonstrated on sl(3,O), and constructs an abelian group to distinguish multiple real forms.

Contribution

It presents a novel approach to classify real forms of e6 using Cartan decompositions and Killing form data, and constructs an abelian group to distinguish multiple real forms.

Findings

Identified chains of real subalgebras within e6.

Constructed an abelian group of order 8 acting on real forms.

Distinguished 8 specific copies of the 5 real forms of e6.

Abstract

The process of complexification is used to classify a Lie algebra and identify its Cartan subalgebra. However, this method does not distinguish between real forms of a complex Lie algebra, which can differ in signature. In this paper, we show how Cartan decompositions of a complexified Lie algebra can be combined with information from the Killing form to identify real forms of a given Lie algebra. We apply this technique to sl(3,O), a real form of e6 with signature (52,26), thereby identifying chains of real subalgebras and their corresponding Cartan subalgebras within e6. Motivated by an explicit construction of sl(3,O), we then construct an abelian group of order 8 which acts on the real forms of e6, leading to the identification of 8 particular copies of the 5 real forms of e6, which can be distinguished by their relationship to the original copy of sl(3,O).