PP-waves, M-theory and fluxes

We study a new type of warped compactifications of M-theory on eight-manifolds for which nowhere vanishing covariantly constant spinors of indefinite chirality on the internal manifold can be found. We derive the constraints on the fluxes and the warp factor following from supersymmetry and the equations of motion. We show, that the lift of type IIB pp-waves to M-theory is a special type of solution of this general class of models. We comment on the relation between the type IIB version of such compactifications as a dual description of the Polchinski-Strassler solution describing a four-dimensional confining gauge theory