Unification picture in the minimal supersymmetric $\mathrm{SU}\mathrm{}\left(5\right)\mathrm{}$ model with string remnants

The significant heavy threshold effect is found in the minimal supersymmetric $\mathrm{SU}\mathrm{}\left(5\right)\mathrm{}$ model with two adjoint scalars, one of which is interpreted as a massive string mode largely decoupled from the lower-energy particle spectra. This threshold related with the generic mass splitting of the basic adjoint moduli is shown to alter properly the running of gauge couplings, thus giving a natural solution to the string-scale grand unification. The further symmetry condition of the (top-bottom) Yukawa and gauge coupling superunification at a string scale results in the perfectly working predictions for the top and bottom quark masses in the absence of any large supersymmetric threshold corrections.