Technicolor and other theories of dynamical electroweak symmetry breaking invoke chiral symmetry breaking triggered by strong gauge-dynamics, analogous to that found in QCD, to explain the observed W, Z, and fermion masses. In this talk we describe why a realistic theory of dynamical electroweak symmetry breaking must, relative to QCD, produce an enhanced fermion condensate. We quantify the degree to which the technicolor condensate must be enhanced in order to yield the observed quark masses, and still be consistent with phenomenological constraints on flavor-changing neutral-currents. Lattice studies of technicolor and related theories provide the only way to demonstrate that such enhancements are possible and, hopefully, to discover viable candidate models. We comment briefly on the current status of non-perturbative investigations of dynamical electroweak symmetry breaking, and provide a "wish-list" of phenomenologically-relevant properties that are important to calculate in these theories

In this talk I discuss theories of dynamical electroweak symmetry breaking, with emphasis on the implications of a heavy top-quark on the weak-interaction $\rho$ parameter.

The triviality of the scalar sector of the standard one-doublet Higgs model implies that it is only an effective low-energy theory valid below some cut-off scale A. In this note we show that the experimental constraint on the amount of custodial symmetry violation, |Δρ*| = α|Τ| ≤ 0.4%, implies that the scale Λ must be greater than of order 7.5 TeV. For theories defined about the infrared-stable Gaussian fixed-point, we estimate that this lower bound on ΛA yields an upper bound of approximately 550 GeV on the Higgs boson's mass, independent of the regulator chosen to define the theory. We also show that some regulator schemes, such as higher-derivative regulators, used to define the theory about a different fixed-point are particularly dangerous because an infinite number of custodial-isospin-violating operators become relevant.

Since the pioneering work of Eichten and Lane it has been known that the scale of the interactions responsible for the generation of the strange-quark mass in extended technicolor theories must, absent any Glashow-Iliopoulos-Maiani mechanism for suppressing flavor-changing neutral currents, be greater than of order 1000 TeV. In this paper we point out that the constraint from the neutral D-meson system is now equally strong, implying that the charm quark mass must also arise from flavor dynamics at a scale this high. We then quantify the degree to which the technicolor condensate must be enhanced in order to yield the observed quark masses, if the extended technicolor scale is of order 1000 TeV. Our results are intended to provide a framework in which to interpret and apply the results of lattice studies of conformal strongly interacting gauge theories, and the corresponding numerical measurements of the anomalous dimension of the mass operator in candidate theories of walking technicolor. © 2010 The American Physical Society.

Motivated by models of holographic technicolor, we discuss a four-site deconstructed Higgsless model with nontrivial wave function mixing. We compute the spectrum of the model, the electroweak triple gauge-boson vertices, and, for brane-localized fermions, the electroweak parameters to O(MW2/Mρ2). We discuss the conditions under which αS vanishes (even for brane-localized fermions) and the (distinct but overlapping) conditions under which the phenomenologically interesting decay a1→Wγ is nonzero and suppressed by only one power of (MW/Mρ). © 2008 The American Physical Society.

Anticipating that a dijet resonance could be discovered at the 14 TeV LHC, we present two different strategies to reveal the nature of such a particle; in particular to discern whether it is a quark-antiquark (qq¯), quark-gluon (qg), or gluon-gluon (gg) resonance. The first method relies on the color discriminant variable, which can be calculated at the LHC from the measurements of the dijet signal cross section, the resonance mass, and the resonance width. Including estimated statistical uncertainties and experimental resolution, we show that a qg excited quark resonance can be efficiently distinguished from either a q¯q coloron or a gg color-octet scalar using the color discriminant variable at LHC-14. The second strategy is based on the study of the energy profiles of the two leading jets in the dijet channel. Including statistical uncertainties in the signal and the QCD backgrounds, we show that one can distinguish, in a model-independent way, between gg, qg, and qq¯ resonances; an evaluation of systematic uncertainties in the measurement of the jet energy profile will require a detailed detector study once sufficient 14 TeV dijet data are in hand.

Electrically neutral massive color-singlet and color-octet vector bosons, which are often predicted in theories beyond the Standard Model, have the potential to be discovered as dijet resonances at the LHC. A color-singlet resonance that has leptophobic couplings needs further investigation to be distinguished from a color-octet one. In previous work, we introduced a method for discriminating between the two kinds of resonances when their couplings are flavor universal, using measurements of the dijet resonance mass, total decay width, and production cross section. Here, we describe an extension of that method to cover a more general scenario, in which the vector resonances could have flavor-nonuniversal couplings; essentially, we incorporate measurements of the heavy-flavor decays of the resonance into the method. We present our analysis in a model-independent manner for a dijet resonance with mass 2.5-6.0 TeV at the LHC with s=14TeV and integrated luminosities of 30, 100, 300, and 1000fb-1 and show that the measurements of the heavy-flavor decays should allow conclusive identification of the vector boson. Note that our method is generally applicable even for a Z' boson with non-Standard invisible decays. We include an Appendix of results for various resonance couplings and masses to illustrate how well each observable must be measured to distinguish colorons from Z's.

We study an SU(3)2 axigluon model introduced by Frampton, Shu, and Wang to explain the recent Fermilab Tevatron observation of a significant positive enhancement in the top quark forward-backward asymmetry relative to standard model predictions. First, we demonstrate that data on neutral B d-meson mixing excludes the region of model parameter space where the top asymmetry is predicted to be the largest. Keeping the gauge couplings below the critical value that would lead to fermion condensation imposes further limits at large axigluon mass, while precision electroweak constraints on the model are relatively mild. Furthermore, by considering an extension to an SU(3)3 color group, we demonstrate that embedding the model in an extra-dimensional framework can only dilute the axigluon effect on the forward-backward asymmetry. We conclude that axigluon models are unlikely to be the source of the observed top quark asymmetry. © 2010 The American Physical Society.

In this paper we consider the effects of top-quark compositeness on the electroweak parameters T^ and S^ and the ZbLb̄L coupling. We do so by using an effective field theory analysis to identify several promising patterns of mixing between standard-model-like and vector fermions, and then analyzing simple extensions of the standard model that realize those patterns. These models illustrate four ways in which an extended O(4) symmetry, which controls the size of radiative corrections to the observables discussed, may be broken. These models may also be viewed as highly deconstructed versions of five-dimensional gauge theories dual to various strongly interacting composite Higgs theories. We comment on how our results relate to extra-dimensional models previously considered, and we demonstrate that one pattern of O(4) breaking is phenomenologically favored. © 2011 American Physical Society.