Models Of Dynamical Symmetry Breaking Research Articles

Flavor gauge bosons at the Fermilab Tevatron

We investigate collider signals for gauged flavor symmetries that have been proposed in models of dynamical electroweak symmetry breaking and fermion mass generation. We consider the limits on the masses of the gauge bosons in these models which can be extracted from Tevatron Run I data in dijet production. Estimates of the Run II search potential are provided. We show that the models also give rise to significant signals in single top production which may be visible at Run II. In particular we study chiral quark family symmetry and SU(9) chiral flavor symmetry. The Run I limits on the gauge bosons in these models lie between (1.5-2) TeV and should increase to about 3 TeV in Run II. Finally, we show that an SU(12) enlargement of the SU(9) model, including leptonic interactions, is constrained by low energy atomic parity violation experiments to lie outside the reach of the Tevatron.

Bounds on flavor gauge bosons from precision electroweak data

Gauged flavor symmetries at low energies have been proposed in models of dynamical electroweak symmetry breaking and fermion mass generation. The massive flavor gauge bosons give rise to corrections to precisely measured electroweak quantities. We perform a fit to the collider electroweak data and place indirect limits on such new physics. In particular we study several models from the literature: universal coloron, chiral top color, chiral quark family symmetry, SU(9) and SU(12) chiral flavor symmetry. The $95%$ exclusion limits on the mass of the heavy gauge bosons for these models, at their critical coupling for chiral symmetry breaking, typically lie between 1 and 3 TeV. We discuss the robustness of these bounds with respect to changes in Higgs boson mass, b-quark asymmetry data, the SLD left right asymmetry data, or additional new physics.

Effective electroweak chiral Lagrangian: The matter sector

We parametrize in a model-independent way possible departures from the minimal Standard Model predictions in the matter sector. We only assume the symmetry breaking pattern of the Standard Model and that new particles are sufficiently heavy so that the symmetry is non-linearly realized. Models with dynamical symmetry breaking are generically of this type. We review in the effective theory language to what extent the simplest models of dynamical breaking are actually constrained and the assumptions going into the comparison with experiment. Dynamical symmetry breaking models can be approximated at intermediate energies by four-fermion operators. We present a complete classification of the latter when new particles appear in the usual representations of the $SU(2)_L\times SU(3)_c$ group as well as a partial classification in the general case. We discuss the accuracy of the four-fermion description by matching to a simple `fundamental' theory. The coefficients of the effective lagrangian in the matter sector for dynamical symmetry breaking models (expressed in terms of the coefficients of the four-quark operators) are then compared to those of models with elementary scalars (such as the minimal Standard Model). Contrary to a somewhat widespread belief, we see that the sign of the vertex corrections is not fixed in dynamical symmetry breaking models. This work provides the theoretical tools required to analyze, in a rather general setting, constraints on the matter sector of the Standard Model.

Detecting and studying the lightest pseudo-Goldstone boson at future pp, e+e− and μ+μ− colliders

For an attractive class of dynamical symmetry breaking (technicolor) models, the lightest neutral pseudo-Nambu-Goldstone boson ( P 0) contains only down-type techniquarks and charged technileptons. We discuss the prospects for discovering and studying the P 0 of such models at the Tevatron and the LHC and at future e + e − and μ + μ − colliders. Depending upon the number of technicolors, N TC, discovery of the P 0 at the Tevatron and the LHC in the gg → P 0 → γγ mode could be possible over a wide range of mass. For N TC = 4, we estimate that RunII Tevatron data can be used to exclude or discover a P 0 in the 50–200 GeV mass range, and at the LHC, a very precise measurement of Γ( P 0 → gg) B( P 0 → γγ) will be possible. For N TC = 4, discovery of the P 0 at an e + e − collider via the reaction e + e − → γP 0 should be possible for an integrated luminosity of L = 100 fb −1 at √ s = 500 Gev as long as m P 0 is not near m Z . However, measuring the branching fractions and couplings of the P 0 with precision would require much more luminosity. In the γγ collider mode of operation at an e + e − collider, the γγ → P 0 → b b signal should be very robust and could be measured with high statistical accuracy for a broad range of m P 0 if N TC = 4. For the minimal N TC = 1 case, detection of the P 0 at the Tevatron and in e + e − collisions will be very difficult, and the precision of measurements at the LHC and the γγ collider decline markedly. Only a μ + μ − collider yields a P 0 production rate that does not depend markedly upon N TC. At a μ + μ − collider, depending upon the luminosity available at low energies, discovery of the P 0 as an s-channel resonance (given its predicted coupling to μ + μ −) should prove possible via scanning, even if it has not already been detected elsewhere. Once the precise mass of the P 0 is known, operation of the μ + μ − collider as a P 0 factory will typically allow precision measurements of enough observables to determine the number of technicolors of the theory and (up to a discrete set of ambiguities) the fundamental parameters of the low-energy effective Lagrangian describing the Yukawa couplings of the P 0.

Top-bottom splitting in technicolor with composite scalars

We present a model of dynamical electroweak symmetry breaking in which the splitting between the top and bottom quark masses arises naturally. The W and Z masses are produced by a minimal technicolor sector, the top quark mass is given by the exchange of a weak-doublet technicolored scalar, and the other quark and lepton masses are induced by the exchange of a weak-doublet technicolor-singlet scalar. We show that, in the presence of the latter scalar, the vacuum alignment is correct even in the case of SU(2) technicolor. The fit of this model to the electroweak data gives an acceptable agreement (chi-squared = 28 for 20 degrees of freedom). The mass hierarchy between the standard fermions other than top can also be explained in terms of the hierarchy of squared-masses of some additional scalars. We discuss various possibilities for the compositeness of the scalars introduced here.

A dynamical symmetry breaking model in Weyl space

The dynamical process following the breaking of Weyl geometry to Riemannian geometry is considered by studying the motion of de Sitter bubbles in a Weyl vacuum. The bubbles are given in terms of an exact, spherically symmetric thin shell solution to the Einstein equations in a Weyl–Dirac theory with a time-dependent scalar field of the form β=f(t)/r. The dynamical solutions obtained lead to a number of possible applications. An important feature of the thin shell model is the manner in which β provides a connection between the interior and exterior geometries since information about the exterior geometry is contained in the boundary conditions for β.

New vector bosons in the electroweak sector: A renormalizable model with decoupling

A linear realization of a model of dynamical electroweak symmetry breaking describing additional heavy vector bosons is proposed. The model is a $\mathrm{SU}{(2)}_{L}\ensuremath{\bigotimes}\mathrm{U}(1)\ensuremath{\bigotimes}\mathrm{SU}{(2)}_{L}^{\ensuremath{'}}\ensuremath{\bigotimes}\mathrm{SU}{(2)}_{R}^{\ensuremath{'}}$ gauge theory, breaking at some high scale $u$ to ${\mathrm{SU}(2)}_{\mathrm{weak}}\ensuremath{\bigotimes}\mathrm{U}{(1)}_{Y}$ and breaking again in the standard way at the electroweak scale $v$ to ${\mathrm{U}(1)}_{\mathrm{em}}.$ The model is renormalizable and reproduces the standard model in the limit $u\ensuremath{\rightarrow}\ensuremath{\infty}.$ This decoupling property is shown to hold also at the level of radiative corrections by computing, in particular, the \ensuremath{\epsilon} parameters.

Erratum: Conformal phase transition in gauge theories [Phys. Rev. D55, 5051 (1997)

The conception of the conformal phase transiton (CPT), which is relevant for the description of non-perturbative dynamics in gauge theories, is introduced and elaborated. The main features of such a phase transition are established. In particular, it is shown that in the CPT there is an abrupt change of the spectrum of light excitations at the critical point, though the phase transition is continuous. The structure of the effective action describing the CPT is elaborated and its connection with the dynamics of the partially conserved dilatation current is pointed out. The applications of these results to QCD, models of dynamical electroweak symmetry breaking, and to the description of the phase diagram in (3+1)-dimensional $ SU(N_c)$ gauge theories are considered.

$$Z \to b\bar b$$ probability and asymmetry in a model of dynamical electroweak symmetry breaking

The deviations from the Standard Model in the probability of \(Z \to b\bar b\) decay and in the forward-backward asymmetry in the reaction \(e^ + e^ - \to b\bar b\) are studied in the framework of the model of dynamical electroweak symmetry breaking, the essential feature of which is the existence of a triple anomalous W-boson vertex in a region of momenta restricted by a cutoff Λ. We obtain a set of equations for additional terms in the \(Wb \bar t\) vertex and apply its solution to the process \(Z \to b\bar b\). We show that it is possible to obtain a consistent description of both deviations, which is quite nontrivial because these effects are not simply correlated. The necessary value of the anomalous W interaction coupling, λ=−0.22±0.01, is consistent with existing bounds and leads to definite predictions, e.g., for pair W production in e+e− collisions at LEP200.

Conformal phase transition in gauge theories

The conception of the conformal phase transiton (CPT), which is relevant for the description of nonperturbative dynamics in gauge theories, is introduced and elaborated. The main features of such a phase transition are established. In particular, it is shown that in the CPT there is an abrupt change of the spectrum of light excitations at the critical point, though the phase transition is continuous. The structure of the effective action describing the CPT is elaborated and its connection with the dynamics of the partially conserved dilatation current is pointed out. The applications of these results to QCD, models of dynamical electroweak symmetry breaking, and to the description of the phase diagram in (3+1)-dimensional SU${(N}_{c})$ gauge theories are considered.

Isospin Breaking and the Top Quark Mass in Models of Dynamical Electroweak Symmetry Breaking

In this talk we review the physics of top-quark mass generation in models of dynamical electroweak symmetry breaking and the constraints on this physics arising from limits on the deviation of the weak interaction $\rho$-parameter from one. We then discuss top-color assisted technicolor in this context.

Vector-Like Strong Coupling Theory with Small S and T Parameters

We propose a mechanism which can reduce the Peskin and Takeuchi's S, T and U parameters in dynamical electroweak symmetry breaking models. It is interesting that not only S but also T parameter can become small even if there exists large isospin violation in fermion condensation. For example, when we take the $SU(2)_L\times U(1)_Y$ breaking mass of up-type fermion $m_U=1$ TeV and that of down-type $m_D=0$, we get S$\sim 0.001 N$ and T$\sim 0.05 N$ for the $SU(2)_L\times U(1)_Y$ invariant masses $M=10$ TeV. The point is that these parameters are suppressed by $SU(2)_L\times U(1)_Y$ invariant masses which the vector-like fermions can have.

Z-->bb-bar versus dynamical electroweak symmetry breaking involving the top quark.

In models of dynamical electroweak symmetry breaking which sensitively involve the third generation, such as top quark condensation, the effects of the new dynamics can show up experimentally in Z->b\bar{b}. We compare the sensitivity of Z->b\bar{b} and top quark production at the Tevatron to models of the new physics. Z->b\bar{b} is a relatively more sensitive probe to new strongly coupled U(1) gauge bosons, while it is generally less sensitive a probe to new physics involving color octet gauge bosons as is top quark production itself. Nonetheless, to accomodate a significant excess in Z->b\bar{b} requires choosing model parameters that may be ruled out within run I(b) at the Tevatron.

Effects of isodoublet colour-octet scalar bosons on oblique electroweak parameters

Isodoublet colour-octet scalar bosons appear in a natural extension of the minimal dynamical symmetry breaking model triggered by a tt condensate, which is geared to yield the top mass in the phenomenologically expected region. We study the effect of these bosons on oblique electroweak parameters S and T, and constrain the mass splitting between the neutral and the charged member of the colour octet. It is also shown that S can be substantially negative, depending on the way the masses in the coloured doublet are split.

Stability of fine tuned hierarchies in strongly coupled chiral models

A fine tuned hierarchy between a strongly coupled high energy compositeness scale and a much lower chiral symmetry breaking scale is a requisite ingredient in many models of dynamical electroweak symmetry breaking. Using a nonperturbative continuous Wilson renormalization group equation approach, we explore the stability of such a hierarchy against quantum fluctuations.

Majorana neutrino masses can save one-family technicolour models

We make non-perturbative estimates of the electroweak radiative correction parameter S in dynamical symmetry breaking models with Majorana neutrino masses. The Majorana masses are treated as perturbations to a non-local chiral model of the strong interactions. We argue that parameter ranges exist that would allow realistic values of S and T in one-family technicolour models.

Critical constraints on chiral hierarchies.

Critical dynamics constrains models of dynamical electroweak symmetry breaking in which the scale of high-energy physics is far above 1 TeV. A big hierarchy requires the high-energy theory to have a second-order chiral phase transition, near which the theory is described by a low-energy effective Lagrangian with composite ``Higgs'' scalars. As scalar theories with more than one ${\mathrm{\ensuremath{\Phi}}}^{4}$ coupling can have a Coleman-Weinberg instability and a first-order transition, such dynamical EWSB models cannot always support a large hierarchy. If the large-${\mathit{N}}_{\mathit{c}}$ Nambu--Jona-Lasinio model is a good approximation to the top-condensate and strong extended technicolor models, they will not produce acceptable EWSB.

Leptoquark model of dynamical electroweak symmetry breaking.

Following a discussion of several simple gauge models for deriving four-fermion interactions to drive dynamical electroweak symmetry breaking in the spirit of Bardeen, Hill, and Lindner, we present a leptoquark model to this end. Consistency conditions fix the relevant couplings and fine-tuning fixes the scale of new physics. The need for such a fundamental theory is discussed, as is the difficulty that these theories present towards performing the necessary calculations with them, i.e., computing the lowest-dimension four-fermion interaction terms as well as higher-dimension operators.

Bethe-Salpeter approach to the top mode standard model

We discuss a Bethe-Salpeter (BS) approach to the minimal dynamical symmetry breaking model where the electroweak symmetry is broken by a condensate of top quarks. We solve the Schwinger-Dyson (SD) gap equation for the top-quark self-energy function in the approximation of keeping only leading-log QCD corrections. We then insert this solution into the BS amplitude for t t→ t t scattering, including dominant QCD corrections in Landau gauge and make a numerical search for poles in the pseudoscalar and scalar channels. Predictions for the Higgs boson mass in this approximation are given and compared with the results from renormalization group (RG) analysis. The two sets of results are found to be in reasonable agreement. A four-family model is consideed and results from both RG and BS analysis are compared. Our result show good agreement between the two approaches even in the low cut-off region Λ = 1–10 TeV where the RG predictions are least reliable.

Dynamical axion for dynamical electro-weak symmetry breaking

We extend the Bardeen-Hill-Lindner dynamical electro-weak symmetry breaking model to include the Pecci-Quinn mechanism. We take advantage of the fact that the coupled gap equations admit a critical line, parametrized by a U (1) A-violating coupling, along which m b m t stays fixed even for m b, t →0. A dynamical Dine-Fishler-Srednicki mechanism triggered by a ṽ Rv R condensate is constructed, offering novel neutrino-axion physics. U (1) PQ plays then the role of an axial family group.