Effective orientifolds from broken supersymmetry

We recently proposed a class of type IIB vacua that yield, at low energies, four-dimensional Minkowski spaces with broken supersymmetry and a constant string coupling. They are compactifications with an internal five-torus bearing a five-form flux phi and warp factors depending on a single coordinate. The breaking of supersymmetry occurs when the internal space includes a finite interval. A probe-brane analysis revealed a gravitational repulsion and a charge attraction of equal magnitude from the left end of the interval, together with a singularity at the other end. Here we complete the analysis revealing the presence, at one end, of an effective O3 of negative tension and positive five-form charge. We also determine the values of these quantities, showing that T=-Q=phi , and characterize the singularity present at the other end of the interval, which hosts an opposite charge. Finally, we discuss various forms of the gravity action in the presence of a boundary and identify a self-adjoint form for its fluctuations.Invited contribution to the special issue of Journal of Physics A: Mathematical and Theoretical on 'Fields, Gravity, Strings and Beyond: In Memory of Stanley Deser'