ELECTROWEAK SYMMETRY-BREAKING BY VECTOR-LIKE FERMION CONDENSATION WITH SMALL S-PARAMETERS AND T-PARAMETERS

In order to build realistic models in which electroweak symmetry is dynamically broken we should explain the smallness of the Peskin-Takeuchi S and T parameters. In accordance with the decoupling theorem, these parameters must be suppressed by SU(2)(L)xU(1)(Y) invariant masses. From this fact we can expect that if fermions with large SU(2)(L)xU(1)(Y) invariant masses undergo condensation and break electroweak symmetry, the S and T parameters can be small. It is interesting that not only the S but also the T parameter can become small even if there exists a large isospin violation in fermion condensation. In this paper we examine the possibility that, by the strong four-Fermi interaction, massive vectorlike fields undergo condensation and break electroweak symmetry. The model becomes almost the same as the standard model at a low energy scale and predicts a heavy Higgs boson. Moreover, we discuss a model in which the four-Fermi interaction can be induced by massive gauge boson exchange. In this model, the masses of ordinary matter fermions (quark and lepton) are enhanced.