Simplicity III

We discuss the general structure of finite dimensional real Lie groups, which is called the Levi decomposition theorem. According to this classical result, any Lie group (up to global topology) splits as a semi-direct product of a non-semisimple part and of a semisimple part. In traditional gauge theory / field theory folklore mostly, only semisimple groups are considered. We will argue, that quite possibly non-semisimple, in particular so-called nilpotent Lie groups could also play a role for new kind of unification mechanisms.