  We investigate maximally symmetric backgrounds in nonsupersymmetric string
vacua with D-branes and O-planes localized in the compact space. We find a
class of solutions with a perturbative string coupling constant in all regions
of spacetime. Depending on the particular model, we find either a time
evolution with a big-bang type singularity or a space dependent background with
generically orbifold singularities. We show that the result can be interpreted
as a supersymmetric bulk with some symmetries broken by the boundaries. We also
discuss an interesting connection to Lorentzian and Euclidian orbifolds.

High Energy Physics - Theory