Heavier fermions and fine-tuning problem in top-quark condensate scheme

Abstract

The analysis in the bubble approximation indicates that a heavier quark-lepton generation with the degenerate mass ${m}_{U}$ in the range 163-353 GeV added in the top-quark condensate scheme could make the momentum cutoff $\ensuremath{\Lambda}$ come down to ${10}^{6}$-5\ifmmode\times\else\texttimes\fi{}${10}^{3}$ GeV when ${m}_{t}=160$ GeV is taken. This could greatly alleviate the fine-tuning problem. The Higgs boson ${\ensuremath{\varphi}}_{S}^{0}$ will obey the mass constraint $2{m}_{t}<{m}_{{\ensuremath{\varphi}}_{S}^{0}}<2{m}_{U}$. The maximal number of the allowed heavy fermion generations is estimated and the possible compositeness origin of the effective four-fermion interactions is discussed.