Higher-dimensional operators to the rescue of minimal SU(5)

Abstract

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, M_U, 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 sin²θ_W and a_s derived from LEP, and also with the experimental constraints on M_U coming from proton lifetime.