Very Large Intermediate Breaking Scale In The Gepner Three Generation   Model
  A detailed study of the intermediate symmetry breaking scale, via the renormalization group equations, for a three generation heterotic string model arising from the N=2 superconformal construction is reported. The numerical study shows that the model admits a very large intermediate breaking scale $\op{>}{\sim}1.0\times10^{16}$ GeV. The role of the gauge singlets in this model is studied, and it is found that these fields play a crucial role in determining the directions and the scale of the intermediate symmetry breaking. The importance of the mixing in generation space is also studied. The generation mixing terms are found to have special effects in the intermediate symmetry breaking. Remarkably these terms can produce some {\it new} Yukawa couplings (not present at the Planck scale) through loops. These couplings are in general very small compared to the ones with non-vanishing tree level values and thus offer a {\it new} mechanism to solve the lepton/quark mass hierarchy problem. 
Jizhi Wu and Richard Arnowitt