Abstract :
A remarkable success of the superstring standard-like models is the correct prediction of the top quark mass, assuming the Minimal Supersymmetric Standard Model below the string scale. Recently it was shown that gauge coupling unification in these models requires additional matter at intermediate energy scales. I obtain the top, bottom and tau lepton Yukawa couplings by calculating tree level string amplitudes. I study the effect of the intermediate matter on the top quark mass prediction. Agreement with αstrong, sin2 θW and αem−1, at Mz, is imposed. The top quark mass prediction is in the range 192 – 200 GeV, and the ratio λb(Mz)λτ(Mz) agrees with experiment.
