Abstract
Possible structures of the gauge hierarchy of interactions are investigated for grand unification models, especially for the SU(L) model. Several sum rules are derived, which are relations between α, α_S sin^2θ_W and possible threshold masses M_i of new interactions. These sum rules reveal clearly and quantitatively correlations between the enlargement of the colour group and that of the fla - vour one. By applying these sum rules, possible steps of enlargement and the corresponding thre-shold masses M_i are analyzed numerically. The modified SU(L) model with sin^2θ_w≠3/8 at the unification mass is discussed also, which involves new quarks with charge Q≠n/3 and/or new leptons with fractional charge.
