N=1 no-scale supergravity from IIB orientifolds

We describe the low-energy effective theory of N = 1 spontaneously broken supergravity obtained by flux-induced breaking in the presence of n D3-branes. This theory can be obtained by integrating out three massive gravitino multiplets in the hierarchical breaking N = 4 --> 3 --> 2 --> I of a N = 4 orientifold. This integration also eliminates the IIB complex dilaton. The resulting theory is a no-scale supergravity model, whose moduli are the three chiral multiplets that correspond to the three radii of T-2 x T-2 x T-2 in T-6, together with the 6n brane coordinates. The U(n) gauge interactions on the branes respect the no-scale structure, and the N = 1 goldstino is the fermionic partner of the T-6 volume. (C) 2002 Published by Elsevier Science B.V.