Top Quark Condensation Research Articles

Heavier fermions and fine-tuning problem in top-quark condensate scheme

The analysis in the bubble approximation indicates that a heavier quark-lepton generation with the degenerate mass ${m}_{U}$ in the range 163-353 GeV added in the top-quark condensate scheme could make the momentum cutoff $\ensuremath{\Lambda}$ come down to ${10}^{6}$-5\ifmmode\times\else\texttimes\fi{}${10}^{3}$ GeV when ${m}_{t}=160$ GeV is taken. This could greatly alleviate the fine-tuning problem. The Higgs boson ${\ensuremath{\varphi}}_{S}^{0}$ will obey the mass constraint $2{m}_{t}<{m}_{{\ensuremath{\varphi}}_{S}^{0}}<2{m}_{U}$. The maximal number of the allowed heavy fermion generations is estimated and the possible compositeness origin of the effective four-fermion interactions is discussed.

Scalar top-quark condensation during the electroweak phase transition.

In the simplest extension of the minimal supersymmetric model, it is shown that there is a range of parameters for which the scalar top quark acquires a vacuum expectation value during a brief period after the onset of the electroweak phase transition. In this case, electromagnetism is temporarily broken, causing efficient annihilation of magnetic monopoles. Also, the temporary spontaneous violation of baryon number may have interesting consequences for models of electroweak baryogenesis.

Tumbling top-quark condensate model.

We propose a renormalizable model with no fundamental scalars which breaks itself in the manner of a "tumbling" gauge theory down to the standard model with a top-quark condensate. Because of anomaly cancellation requirements, this model contains two color-sextet fermions (quixes), which are vector-like with respect to the standard-model gauge group. The model also has a large number of pseudo Nambu-Goldstone bosons, some of which can be light. The top-quark condensate is responsible for breaking the electroweak gauge symmetry and gives the top quark a large mass. We discuss the qualitative features and instructive shortcomings of the model in its present form. We also show that this model can be naturally embedded into an aesthetically pleasing model in which the standard-model fermion families appear symmetrically.

Top quark mass in top quark condensation model

The top quark mass m t in the top quark condensation model is calculated with the ladder Schwinger-Dyson equation including the gluon exchange. Instead of the Pagels-Stokar approximation, for fixing the value of the coupling constant the Goldstone boson decay constant is calculated with the solution of the covariant Bethe-Salpeter equation corresponding to the Goldstone boson. By introducing an interaction of the form ( g′ Λ 2 ) Ψ ̄ L iλ a t R t R λ aΨ L i in the model an m t value lower than 200 GeV can be obtained. The effect of higher dimensional operators is investigated.

Heavy quark condensates from dynamically broken flavour symmetry

We study the dynamics of top quark condensation induced by gauge interactions resulting from a broken flavour symmetry. The gap equation in dressed ladder approximation is solved numerically to obtain directly the top quark mass. The new high energy dynamics reduces the prediction of m t somewhat, but the usual problems of m t being too large and fine tuning remain. In order to solve these problems we extend our discussion to include fourth generation quark condensates.

Two-loop renormalization-group-improved top-quark and Higgs-boson masses in the top-quark condensate model.

We study the sensitivity of the top-quark and Higgs-boson masses in the top-quark condensate model to two-loop radiative corrections. The composite theory, including a higher-dimensional Suzuki operator, provides the two-loop renormalization-group equations of the standard model with ultraviolet boundary conditions. Both the top-quark and the Higgs-boson masses vary by a few GeV with respect to their values in the one-loop calculation.

Dynamical-symmetry-breaking solution to the problem of flavor.

We propose a fully dynamical ``moose'' model with a top-quark condensate. The scale of new physics \ensuremath{\Lambda} may be in the TeV range with flavor-changing neutral currents protected by a Glashow-Iliopoulos-Maiani mechanism.

Comment on critical instability

Abstract We discuss the problem of the mass splitting berween top and bottom quarks, within the context of Nambu-Jona-Lasinio type models involving top and bottom quark condensates. We interpret the phenomenon of “critical instability” recently proposed to account for such a mass splitting as the fine-tuning of two vacuum expectation values in a composite two-Higgs doublet model.

VACUUM ALIGNMENT IN THE TOP MODE STANDARD MODEL

We study the vacuum alignment in the top mode Standard Model in which the electroweak symmetry breaking is triggered by the top quark condensation. Including the QCD effects through the Cornwall-Jackiw-Tomboulis effective potential, we establish that the correct electroweak symmetry breaking SU (2)L × U (1)Y → U (1) em occurs in this model in 1/N leading and improved ladder approximation.

The equivalence of the top quark condensate and the elementary Higgs field

Several recent works suggested to replace the fundamental Higgs boson by a top quark condensate in analogy with the Nambu-Jona-Lasinio (NJL) mechanism. We show that the field theoretically correct replacement is a generalized NJL model with the minimal choice of three independent interaction terms in the lagrangian. We demonstrate in the large- N color limit that the physics of this model is fully equivalent to the corresponding simplified Standard Model where the Higgs boson is represented by an elementary scalar field with the usual Yukawa- and self-interactions. The generalized NJL mechanism does not lead to new physical predictions or constraints and the complete parameter range of the simplified Standard Model is recovered. Since there exists a simple mapping between the couplings of these two models, it is difficult to give physical significance to notions like composite versus fundamental, or dynamical symmetry breaking in this scheme. We also present some new numerical results on the relevant phase diagrams.

Dynamical symmetry breaking by a top quark condensate in the standard model

We consider the possibility that dynamical symmetry breaking is driven by massive scalar exchange. It is shown that after symmetry breaking the original scalar field has a light component and must be kept in the low-energy effective lagrangian. A method of regularisation is developed to allow for the derivation of a gap equation applicable in this case. The analysis is applied to the standard model for the case of positive scalar mass squared and large top quark Yukawa coupling. The spectrum of the model is determined and implications for the masses of the top quark and Higgs boson are considered.

Topcolor: top quark condensation in a gauge extension of the standard model

We describe a color embedding, SU(3) c→SU(3) 1×SU(3) 2, that is designed to break electroweak symmetries through top quark condensation. The minimal scheme of Bardeen, Hill and Lindner can be recovered by taking the scale of embedding large and fine-tunning the ratio of coupling constants. Models of this kind allow computation of the strength of higher dimension operators which are found to be small. Perhaps fine-tunning can ultimately be avoided in this scheme.

Composite Higgs bosons from composite top quarks

We consider theories beyond the top mode standard model in which quarks, leptons and Higgs bosons are all composite. The compositeness of the top quarks leads to contact operators in the low energy theory which may lead to a top quark condensate, and hence electroweak symmetry breaking via a composite effective Higgs doublet.

Vacuum alignment in the top quark condensation

We study the vacuum alignment in the top quark condensate model which can be the two Higgs doublet model as the low energy effective theory. Although in the two Higgs doublet model the vacuum is not always aligned to conserve the U (1) em symmetry, we show through the effective potential that the vacuum in the top quark condensate model is actually aligned to conserve the U (1) em symmetry.

Minimal dynamical symmetry breaking of the standard model.

We formulate the dynamical symmetry breaking of the standard model by a top-quark condensate in analogy with BCS theory. The low-energy effective Lagrangian is the usual standard model with supplemental relationships connecting masses of the top quark, $W$ boson, and Higgs boson which now appears as a $\overline{t}t$ bound state. Precise predictions for ${m}_{t}$ and ${m}_{H}$ are obtained by abstracting the compositeness condition for the Higgs boson to boundary conditions on the renormalization-group equations for the full standard model at high energy.