A kind of prediction from superstring model building

Assuming that the Standard Model of Particle Physics arises from the $E_8\times E_8$ Heterotic String Theory, we try to solve the discrepancy between the unification scale predicted by this theory ($\approx g_{GUT}\times 5.27\cdot 10^{17}$ GeV) and the value deduced from LEP experiments ($\approx 2\cdot 10^{16}$ GeV). A crucial ingredient in our solution is the presence at low energies of three generations of supersymmetric Higgses and vector-like colour triplets. As a by-product our analysis gives rise to a strategy which might be useful in order to construct realistic models.