Low energy implications of minimal superstring unification

We study the phenomenological implications of effective supergravities based on string vacua with spontaneously broken N = 1 supersymmetry by dilaton and moduli F-terms. We further require minimal string unification, namely that large string threshold corrections ensure the correct unification of the gauge couplings at the grand unification scale. The whole supersymmetric mass spectrum turns out to be determined in terms of only two independent parameters, the dilaton-moduli mixing angle and the gravitino mass. In particular we discuss the region of the parameter space where at least one superpartner is “visible” at LEPII. We find that the most likely candidates are the scalar partner of the right-handed electron and the lightest chargino, with interesting correlations between their masses and with the mass of the lightest higgs. We show how discovering SUSY particles at LEPII might rather sharply discriminate between scenarios with pure dilation SUSY breaking and mixed dilaton-moduli breaking.