HIGHER-DIMENSIONAL OPERATORS TO THE RESCUE OF MINIMAL SU(5)

We consider the modification of the minimal SU(5) Lagrangian due to higher-dimensional operators, arising from quantum gravity effects or from spontaneous compactification of extra dimensions in Kaluza-Klein type theories. Due to these operators the SU(3)c, SU(2)L and U(1)Y couplings do not meet at all at the unification scale, MU, and the magnitudes of the mismatch are directly related to the couplings of the higher-dimensional operators. In particular, we consider five- and six-dimensional operators and show that a large range of values of couplings of these operators are compatible with the latest values of sin2 θW and as derived from LEP, and also with the experimental constraints on MU coming from proton lifetime.