The Generalised Jacobson-Morosov Theorem - Memoirs of the American Mathematical Society

Considers homomorphisms H \to K from an affine group scheme H over a field k of characteristic zero to a proreductive group K. Using a general categorical splitting theorem, André and Kahn proved that for every H there exists such a homomorphism which is universal up to conjugacy. The author gives a purely group-theoretic proof of this result.