Phenomenology of a top quark seesaw model

The top quark seesaw mechanism offers a method for constructing a composite Higgs field without the usual difficulties that accompany traditional technicolor or top-color theories. The focus of this article is to study the phenomenology of the new physics required by this mechanism. After establishing a set of criteria for a plausible top quark seesaw theory, we develop two models, the first of which has a heavy weak singlet fermion with hypercharge $\frac{4}{3}$ while the second has, in addition, a heavy weak singlet hypercharge -$\frac{2}{3}$ fermion. At low energies, these theories contain one or two Higgs doublets, respectively. We then derive the low energy effective Higgs potential in detail for the two-doublet theory as well as study the likely experimental signatures for both theories. A strong constraint on the one-doublet model is the measured value of the ρ parameter which permits the new heavy fermion to have a mass of about 5–7 TeV, when the Higgs boson has a mass greater than 300 GeV. In the two-doublet model, mixing of the new heavy $Y=-\frac{2}{3}$ fermion and the b quark affects the prediction for $R_b.$ In order to agree with the current limits on $R_b,$ the mass of this fermion should be at least 12 TeV. The mass of the heavy $Y=\frac{4}{3}$ fermion in the two-doublet model is not as sharply constrained by experiments and can be as light as 2.5 TeV.