Soft SUSY breaking, dilaton domination and intermediate scale string models

We present an analysis of the low-energy implications of an intermediate sc ale (similar to 10(11) GeV) string theory. We mainly focus on the evolution of the physical parameters under the renormalisation group equations (RGEs ) and find several interesting new features that differ from the standard G UT scale or Planck scale scenarios. We give a general discussion of soft su persymmetry breaking terms in type-I theories and then investigate the reno rmalization group running. In the dilaton domination scenario, we present t he sparticle spectra, analysing constraints from charge and colour breaking , fine tuning and radiative electroweak symmetry breaking. We compare with the allowed regions of parameter space when the RGEs start running at the s tandard GUT or the intermediate scales, and find quite remarkably that the dilaton dominated supersymmetry breaking scenario, which is essentially rul ed out from constraints on charge and colour breaking if the fundamental sc ale is close to the Planck mass, is allowed in a large region of parameter space if the fundamental scale is intermediate.