Search

The radiative decays of vector mesons in the context of Zweig's rule and SU(3) breaking are examined. It is found that a general amplitude for the decays can be expressed in terms of seven parameters and it is solved for these parameters by fitting to the experimental data. It is found that the nonrelativistic quark model gives a reasonable explanation for the sizes of these parameters.

We comment on the calculation by Voloshin and Zakharov of the rate of decay of a light Higgs Boson into pions.

We discuss the difficulties with anomaly constraints and flavor breaking involved in building a composite technicolor standard model. We construct a model of quarks with the required symmetry properties.

If quarks and leptons are composite objects with common constituents, then there exist two-quark-two-lepton contact interactions which could affect lepton pair production at the SSC. We show that for a range of compositeness scales and lepton pair invariant masses, the contact interaction contributions dominate the standard model contributions to the cross section. In this regime, we show that there should be a measurable and statistically significant front-back asymmetry.

If quarks and leptons are composite objects with common constituents, then there will be two-quark-two-neutrino contact interactions which will increase the number of events with missing transverse momentum observed at the SSC. We show that, if the scale of compositeness λ ∗ is only moderately high, such effects should be observable.

We comment on the calculation of Voloshin and Zakharov of the couplings of a light Higgs boson to pions and extend their analysis to consider flavor-changing Higgs-pion couplings, including K→ ϕ ev and K→ ϕπ .

We reexamine the bounds on a very light Higgs boson (φ) coming from limits on the decays K→ π + φ and B→ φ +X. We show that, if there are only three families, m φ >2 m τ , and that regardless of the number of families M φ >360 MeV.

We show that the mechanism which enhances ordinary fermion masses and raises the masses of pseudo Goldstone bosons in walking-technicolor models may also lead to an enhancement of weak-isospin\char21{}violating effects of extended-technicolor interactions. We discuss the constraints on these models due to limits on the deviation of the \ensuremath{\rho} parameter from 1.

We consider the effect of an ultraheavy quark (mass of quark greater than mass of the W-boson) of charge 2 3 on K 0 - K 0 mixing. The calculation is done in the effective field theory formalism and the effect of QCD renormalization is included (to one loop).

In models in which both light fermions and technifermions are composite objects with common constituents, the couplings of the massive electroweak gauge bosons to light quarks and leptons can differ from their standard model counterparts. We consider the effects of the modified gauge boson couplings on low energy neutral current phenomenology and on the properties of the Z boson. We show that precise measurements at LEP and SLC of the total width of the Z, ratio of leptonic to hadronic partial widths, and left-right and forward-backward asymmetries should probe compositeness scales of 1–2.5 TeV.

An alternative structure of electroweak symmetry breaking based on an SU(4)/SU (2) symmetry breaking pattern is discussed. An effective chiral lagrangian describing the pseudo-Goldstone bosons and gauge bosons is constructed and their interactions are analyzed. It is shown that the model contains doubly charged pseudo-Goldstone bosons which couple to two similarly charged W's. The question of vacuum alignment is considered, and it is shown that if an additional discrete symmetry is imposed, a custodial SU (2) preserving vacuum is a global minimum of the potential (for a range of coefficients in the effective chiral lagrangian).

From the patterns of the quark mass matrices observed in two and three generations of quarks, a plausible form of the quark mass matrix with phases (of multiples of ½ π) is proposed for four generations of quarks. This allows the determination of the entire 4 × 4 KM matrix as a function of just two unknowns (mb′ and mt′), and the allowed mass ranges of the 4th generation quarks (which we call b′ and t′) are obtained from the present constraints on the KM matrix in the first 3-generation sector. The possibility of a light 4th generation quark (mb′ 0.1. It is pointed out that UA1's t-quark data may also contain the b′-quark with mb′ ⩽ 50 GeV, and in this case, mt′ is shown to be bounded from above, mt′ ⩽ 190 GeV. Some low-energy phenomenology such as B0 − B0 mixing and CP violation, in which the effects of the 4th generation quarks may be observable, are also considered. The main result is that the mixing parameter Rodd for B0d − B0d is 5–6 times larger than in the 3-generation case and may be observable (Rodd ∼ 10%) if the uncertainties in the parameters used are taken into account. The CP-violating parameter l± is shown to be too small to be observed (O(10−4−10−6)) for both B0d and Bs0, while the mixing parameter Rodd for Bs0 − Bs0 is shown to be definitely observable (Rodd > 50%) regardless of the 4th generation quark masses.

It is shown that the large-N approximation in the standard model predicts much too small a rate for ΔI = 1 2 nonleptonic K decays, even when short-distance QCD effects such as penguins are included. The effects of the penguins are discussed consistently to leading nontrivial order in chiral perturbation theory and it is found that they are completely calculable and small. It is concluded that N = 3 is not large enough to make the large-N approximation useful.

The low-energy properties of a compactified five-dimensional gauge theory can be reproduced in a four-dimensional theory with a replicated gauge group and an appropriate gauge symmetry breaking pattern. The lightest vector bosons in these “deconstructed” or “remodeled” theories have masses and couplings approximately equal to those of the Kaluza–Klein tower of massive vector states present in a compactified higher-dimensional gauge theory. We analyze the unitarity of low-energy scattering of the massive vector bosons in a deconstructed theory, and examine the relationship between the scale of unitarity violation and the scale of the underlying chiral symmetry breaking dynamics which breaks the replicated gauge groups. As in the case of compactified five-dimensional gauge theories, low-energy unitarity is ensured through an interlacing cancellation among contributions from the tower of massive vector bosons. We show that the behavior of these scattering amplitudes is manifest without such intricate cancellations in the scattering of the would-be Goldstone bosons of the deconstructed theory. Unlike compactified five-dimensional gauge theories, the amplitude for longitudinal vector boson scattering in deconstructed theories does grow with energy, though this effect is suppressed by 1/(N+1), with N+1 being the number of replicated gauge groups.

In this note I provide a brief description of models of dynamical electroweak symmetry breaking, including walking technicolor, top‐color assisted technicolor, the top‐quark seesaw model, and little higgs theories.

Simple models of topcolor and topcolor-assisted technicolor rely on a relatively strong U(1) gauge interaction to ``tilt'' the vacuum. This tilting is necessary to produce a top-condensate, thereby naturally obtaining a heavy top-quark, and to avoid producing a bottom-condensate. We identify some peculiarities of the Nambu-Jona-Lasinio approximation often used to analyze the topcolor dynamics. We resolve these puzzles by constructing the low-energy effective field theory appropriate to a mass-independent renormalization scheme. We construct the power-counting rules for such an effective theory. By requiring that the Landau pole associated with the U(1) gauge theory be sufficiently above the topcolor gauge boson scale, we derive an upper bound on the strength of the U(1) gauge-coupling evaluated at the topcolor scale. The upper bound on the U(1) coupling implies that these interactions can shift the composite Higgs boson mass-squared by only a few per cent and, therefore, that the topcolor coupling must be adjusted to equal the critical value for chiral symmetry breaking to within a few per cent., Comment: 15 pages, LaTeX and Pictex. Minor comments and references added to clarify relation of current work to previous work on composite Higgs models

The triviality of the scalar sector of the standard one-doublet Higgs model implies that this model is only an effective low-energy theory valid below some cut-off scale Lambda. For a heavy higgs this scale must be relatively low (10 TeV or less). Additional interactions coming from the underlying theory, and suppressed by the scale Lambda, give rise to model-dependent corrections to precisely measured electroweak quantities. Dimension six operators arising from the underlying physics naturally contribute to the S and T parameters, and their effects should be included in a global fit to the precision data that determines any limit on the Higgs mass. Using dimensional analysis, we estimate the expected size of these corrections in a custodially-symmetric strongly-interacting underlying theory. Taking these operators' coefficients to be of natural size gives sufficiently large contributions to the T parameter to reconcile Higgs masses as large as 400-500 GeV with the precision data., Comment: 9 pages, 3 epsf figures included

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 Fermilab 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 quark 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 and 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.

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., Comment: 9 pages, 6 Postscript figures, uses epsf.sty, talk presented by RSC at Workshop on Top Quark Physics, Iowa State University, May 25-26, 1995 and Yukawa International Seminar `95, Kyoto, Aug. 21-25, 1995. Minor typo fixed

We review the connection between mt and the Zbb̄ vertex in ETC models and demonstrate the power of the resulting experimental constraint on models with weak-singlet ETC bosons. Some efforts to bring ETC models into agreement with experimental data on the Zbb̄ vertex are mentioned, and the most promising one (non-commuting ETC) is discussed in detail.

In this paper we compute the the one-loop chiral logarithmic corrections to the S and T parameters in a highly deconstructed Higgsless model with only three sites. In addition to the electroweak gauge bosons, this model contains a single extra triplet of vector states (which we denote \rho^{\pm} and \rho^0), rather than an infinite tower of "KK" modes. We compute the corrections to S and T in 'tHooft-Feynman gauge, including the ghost, unphysical Goldstone-boson, and appropriate "pinch" contributions required to obtain gauge-invariant results for the one-loop self-energy functions. We demonstrate that the chiral-logarithmic corrections naturally separate into two parts, a model-independent part arising from scaling below the \rho mass, which has the same form as the large Higgs-mass dependence of the S or T parameter in the standard model, and a second model-dependent contribution arising from scaling between the \rho mass and the cutoff of the model. The form of the universal part of the one-loop result allows us to correctly interpret the phenomenologically derived limits on the S and T parameters (which depend on a "reference" Higgs-boson mass) in this three-site Higgsless model. Higgsless models may be viewed as dual to models of dynamical symmetry breaking akin to "walking technicolor", and in these terms our calculation is the first to compute the subleading 1/N corrections to the S and T parameters. We also discuss the reduction of the model to the ``two-site'' model, which is the usual electroweak chiral lagrangian, noting the ``non-decoupling'' contributions present in the limit as M_\rho goes to infinity., Comment: 58 pages; uses JHEP and axodraw. Extensively corrected to incorporate consistent perturbative expansion, additional pinch contributions, and running of delocalization parameter. Footnotes added