Invariant generalized complex structures on Lie groups

We describe a class (called regular) of invariant generalized complex structures on a real semisimple Lie group G. The problem reduces to the description of admissible pairs (\gk, \omega), where \gk is an appropriate regular subalgebra of the complex Lie algebra \gg^{C} associated to G and \omega is a closed 2-form on \gk, such that a non-degeneracy condition holds. In the case when G is a semisimple Lie group of inner type (in particular, when G is compact) a classification of regular generalized complex structures on G is given. We show that any invariant generalized complex structure on a compact semisimple Lie group G is regular, provided that an additional natural condition holds. In the case when G is a semisimple Lie group of outer type, we describe the subalgebras \gk in terms of appropriate root subsystems of a root system of \gg^{C} and we construct a large class of admissible pairs (\gk ,\omega) (hence, regular generalized complex structures on G).