Detuned Branes and Supersymmetry Breaking

We consider the spontaneous breaking of supersymmetry in five dimensional supergravity with boundaries where the supersymmetry breaking mechanism is provided by the even part of the bulk prepotential. The supersymmetric action comprises boundary brane terms with detuned tensions. The two branes have opposite tensions. We analyse the possible vacua with spontaneously broken supersymmetry. A class of solutions corresponds to rotated branes in an $AdS_5$ bulk. In particular parallel branes which are rotated with respect to the bulk preserve 1/4 of supersymmetry. We analyse more general vacua using the low energy effective action for gravity coupled to the radion field. Supersymmetry breaking implies that the radion field acquires a potential which is negative and unbounded from below. This potential is modified when coupling the boundary branes to a bulk four--form field. For a brane charge larger than the deficit of brane tension, the radion potential is bounded from below while remaining flat when the charge equals the deficit of brane tension.