The Phenomenology of a Top Quark Seesaw Model

TL;DR

This paper explores the phenomenology of top quark seesaw models, proposing two models with heavy fermions and analyzing their low-energy Higgs potential and experimental signatures, including constraints from precision measurements.

Contribution

It develops two specific top quark seesaw models with detailed low-energy effective theories and phenomenological predictions, including experimental constraints.

Findings

Heavy fermion masses are constrained by the rho parameter and R_b measurements.

The one-doublet model allows heavy fermions around 5-7 TeV for Higgs > 300 GeV.

The two-doublet model predicts the Y=-2/3 fermion should be at least 12 TeV.

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 4/3 while the second has, in addition, a heavy weak singlet hypercharge -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 rho 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=-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=4/3 fermion in the two-doublet model is not as sharply constrained by experiments and can be as light as 2.5 TeV.