Non-perturbative unification in the light of LEP results

Abstract

We consider an alternative to conventional grand unified theories originally proposed by Maiani, Parisi and Petronzio, where owing to the existence of extra fermion generations at some intermediate scale, the gauge couplings become large at high energies. We first comment on how the non-supersymmetric version of this scenario is ruled out; we then consider the two-loop evolution of couplings in the supersymmetric extension of this scenario, and check whether such a scenario is feasible in the light of the precise values of couplings now available from LEP.