Top Mass and Isospin Breaking in Dynamical Symmetry Breaking Scenario

We consider a scenario where the top-quark mass is generated dynamically, and study the implication of the present experimental values for mt and the T parameter. We assume technicolor-like scenario for inducing the W mass and an effective four fermi operator for inducing the top-quark mass. We also assume that only this four fermi operator is relevant at low energy. Then we estimate in detail the strength G and the intrinsic mass scale M of the four fermi operator. Unitarity bound is used to quantify the strength of G. We find that G/4π ∼ O(1) and that M is of the order of ΛTC ≃ 1 ∼ 2 TeV or less. Namely the four fermi operator cannot be treated as ‘point-like’ around the electroweak scale. Furthermore we estimate the contribution of the four fermi operator to the T parameter. We find that the QCD correction to the top-quark mass function reduces the contribution to the T parameter by about 40%. By comparing the results with the present experimental bound, we obtain another upper bound on M which is typically in several to 10 TeV region.