Intermediate scales in superstring models consistent with ten-dimensional symmetries

We study intermediate-scale breaking along flat directions (N) in four-dimensional theories consistent with classical symmetries of the ten-dimensional superstring. When supersymmetry is broken in the hidden sector by non-perturbative effects the flatness is lifted by non-renormalizable terms (≅ m3/22vertical strokeNvertical stroke4) in the tree level potential. One-loop gravitational corrections break supersymmetry in the observable sector providing a common mass to all scalars. If the effective theory obtained by integration of the heavy Kaluza-Klein modes is a small correction to the truncated theory, then: (i) Flat directions are necessary to stabilize the φ-fields (corresponding to non-flat directions) at their origin; (ii) The tree level (plus one-loop gravitational corrections) minimum is at <φ>=0, > or approx. n1/2m01/4MP3/4 ≅ 1015 GeV, where m0 < or approx. O(1) TeV is the scale of supersymmetry breaking in the observable sector and n ≅ O(102) the total number of scalar superfields; (iii) At this minimum the soft-breaking scalar masses in the observable sector are mφ2 ≅ 2MP-2mN2 << mN2; (iv) Non-gravitational radiative corrections will communicate the supersymmetry breaking mN2 from the N-sector on the φ-sector, providing an effective breaking (Mφ2)eff = m02 ≅ (αGUT/π)2mN2. The critical temperature associated with the N-phase transition is Tc ≅ (π/αGUT) m0 ≅ 104 GeV. The softening of cosmological problems and the possibility of low-energy baryogenesis at temperatures below Tc are briefly outlined. (orig.)