Weak scale measurement constraints on string models

The result of the modular-invariant one-loop string effective coupling constant for a large class of models is used to discuss the weak scale measurement constraints on superstring models. Superstring models with intermediate gauge symmetry breaking are proposed to account for the grand gauge unification scale MGUT=1016 GeV, which is deduced from the precision weak scale measurement in the minimal SUSY unification model. A gaugino-condensation-induced Hosotani mechanism is suggested for the intermediate gauge symmetry breaking. In this scheme, supergravity, gauge symmetry, and space-time compactification are induced by one nonperturbative dynamics: gaugino condensation. The string scale μs is calculated in intermediate SU(5) string models. A relation between the intermediate gauge symmetry-breaking scale MI=MGUT and string scale is found to be μs3=MImP2. It is argued that this relation is a general result for all the superstring models with intermediate gauge symmetry breaking. The level one minimal SUSY left-right string models are shown to be excluded by weak scale measurement. The constraints on the ratio of affine levels is worked out. It is demonstrated that string unification is more restricted by the experiments than any other unification schemes are