Quantum Restoration of the U(1)_Y Symmetry in Dynamically Broken SUSY-GUT's

Abstract

We propose a supersymmetric hypercolor SU(3)_H gauge theory interacting strongly at the grand unification scale, in which the hyperquark condensation breaks SU(5)_GUT down to SU(3)_C x SU(2)_L without unbroken U(1)_Y at the classical level. However, we show that the broken U(1)_Y symmetry is restored by quantum mechanical effects and hence there remains the standard-model gauge symmetry at the electroweak scale. The dynamics of the strong interactions also produces naturally a pair of massless Higgs doublets. In addition to these Higgs doublets, we have a pair of massless singlets which contributes to the renormalization-group equations of gauge coupling constants and hence affects the GUT unification. We discuss a simple solution to this problem.