Maximally supersymmetric G-backgrounds of IIB supergravity

We classify the geometry of all supersymmetric IIB backgrounds which admit the maximal number of G-invariant Killing spinors. For compact stability subgroups G=G2,SU(3) and SU(2), the spacetime is locally isometric to a product Xn×Y10−n with n=3,4,6, where Xn is a maximally supersymmetric solution of a n-dimensional supergravity theory and Y10−n is a Riemannian manifold with holonomy G. For non-compact stability subgroups, G=K⋉R8, K=Spin(7), SU(4), Sp(2), SU(2)×SU(2) and {1}, the spacetime is a pp-wave propagating in an eight-dimensional manifold with holonomy K. We find new supersymmetric pp-wave solutions of IIB supergravity.