On derivations of subalgebras of real semisimple Lie algebras

摘要

Let g be a real semisimple Lie algebra with Iwasawa decomposition t circle plus a circle plus n. We show that, except for some explicit exceptional cases, every derivation of the nilpotent subalgebra n that preserves its restricted root space decomposition is of the form ad(W), where W is an element of m circle plus a.