One-loop effective potential in D = 4 theories consistent with classical symmetries of D = 10 superstrings

The four-dimensional effective action consistent with classical symmetries of the E₈ × E₈ superstring is studied and compared with the theory obtained by performing a truncation of D = 10 supergravity in which all heavy Kaluza-Klein modes are discarded. It is assumed that supersymmetry is broken in the hidden sector by non-perturbative effects. As in the truncation model, it is found that at free level there are no soft supersymmetry breakings in the observable sector. However, contrary to the truncation result, one-loop corrections break supersymmetry in the observable sector providing a common mass for all matter scalars m₀ ∼ m _{3 2}(m _{3 2}/M_P) ^{1 3}. Finally, in contrast to the truncation model, there are no gauge non-singlet (N) flat directions. These effects generate an intermediate scale 〈 N 〉 {less-than or approximate} m₀ ^{1 4}M_P ^{3 4}.