Phenomenology of a top quark seesaw model

Abstract

The top quark seesaw mechanism offers a method for constructing a composite Higgs field without the usual difficulties that accompany traditional technicolor or topcolor 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 43 while the secon has, in addition, a heavy weak singlet hypercharge −23 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 has a mass greater than 300 GeV. In the two-doublet model, mixing of the new heavy Y = − 23 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 = 43 fermion in the two-doublet model is not as sharply constrained by experiments and can be as light as 2 .5 TeV.