Invariant pseudo Kaehler metrics in dimension four

Four dimensional simply connected Lie groups admitting a pseudo K\"ahler metric are determined. The corresponding Lie algebras are modelized and the compatible pairs $(J,\omega)$ are parametrized up to complex isomorphism (where $J$ is a complex structure and $\omega$ is a symplectic structure). Such structure gives rise to a pseudo Riemannian metric $g$ for which $J$ is parallel. It is proved that most of these complex homogeneous spaces admit a pseudo K\"ahler Einstein metric. Ricci flat and flat metrics are determined. In particular Ricci flat unimodular K\"ahler Lie algebras are flat in dimension four. Other algebraic and geometric features are treated. A general construction of Ricci flat pseudo K\"ahler structures in higher dimensions on some affine Lie algebras is given. Walker and hypersymplectic metrics on Lie algebras are compared.