Higgsless Models: Lessons from Deconstruction

This talk reviews recent progress in Higgsless models of electroweak symmetry breaking, and summarizes relevant points of model-building and phenomenology.Comment: 12 pages, 2 figures, Presented at the X Mexican Workshop on Particles and Field

Oblique Corrections in Deconstructed Higgsless Models

In this talk, using deconstruction, we analyze the form of the corrections to the electroweak interactions in a large class of ``Higgsless'' models of electroweak symmetry breaking, allowing for arbitrary 5-D geometry, position-dependent gauge coupling, and brane kinetic energy terms. Many models considered in the literature, including those most likely to be phenomenologically viable, are in this class. By analyzing the asymptotic behavior of the correlation function of gauge currents at high momentum, we extract the exact form of the relevant correlation functions at tree-level and compute the corrections to precision electroweak observables in terms of the spectrum of heavy vector bosons. We determine when nonoblique corrections due to the interactions of fermions with the heavy vector bosons become important, and specify the form such interactions can take. In particular we find that in this class of models, so long as the theory remains unitary, S - 4 c^2_W T > O(1), where S and T are the usual oblique parameters.Comment: 4 pages, 1 figure, to appear in the proceedings of SUSY 2004 : The 12th International Conference on Supersymmetry and Unification of Fundamental Interactions, held at Epochal Tsukuba, Tsukuba, Japan, June 17-23, 200

Multi-Gauge-Boson Vertices and Chiral Lagrangian Parameters in Higgsless Models with Ideal Fermion Delocalization

Higgsless models with fermions whose SU(2) properties are "ideally delocalized," such that the fermion's probability distribution is appropriately related to the W boson wavefunction, have been shown to minimize deviations in precision electroweak parameters. As contributions to the S parameter vanish to leading order, current constraints on these models arise from limits on deviations in multi-gauge-boson vertices. We compute the form of the triple and quartic gauge boson vertices in these models and show that these constraints provide lower bounds only of order a few hundred GeV on the masses of the lightest KK resonances. Higgsless models with ideal fermion delocalization provide an example of extended electroweak gauge interactions with suppressed couplings of fermions to extra gauge-bosons, and these are the only models for which triple-gauge-vertex measurements provide meaningful constraints. We relate the multi-gauge couplings to parameters of the electroweak chiral Lagrangian, and the parameters obtained in these SU(2) x SU(2) models apply equally to the corresponding five dimensional gauge theory models of QCD. We also discuss the collider phenomenology of the KK resonances in models with ideal delocalization. These resonances are found to be fermiophobic, therefore traditional direct collider searches are not sensitive to them and measurements of gauge-boson scattering will be needed to find them.Comment: 28 pages, 1 eps figure. Typo in reference correcte

Identifying Better Effective Higgsless Theories via W_L W_L Scattering

The three site Higgsless model has been offered as a benchmark for studying the collider phenomenology of Higgsless models. In this talk, we present how well the three site Higgsless model performs as a general representative of Higgsless models in describing W_L W_L scattering, and which modifications can make it more representative. We employ general sum rules relating the masses and couplings of the Kaluza-Klein (KK) modes of the gauge fields in continuum and deconstructed Higgsless models as a way to compare the different theories. After comparing the three site Higgsless model to flat and warped continuum Higgsless models, we analyze an extensions of the three site Higgsless model, namely, the Hidden Local Symmetry (HLS) Higgsless model. We demonstrate that W_LW_L scattering in the HLS Higgsless model can very closely approximate scattering in the continuum models, provided that the parameter `a' is chosen to mimic rho-meson dominance of pi-pi scattering in QCD

General Sum Rules for WW Scattering in Higgsless Models: Equivalence Theorem and Deconstruction Identities

We analyze inelastic 2 to 2 scattering amplitudes for gauge bosons and Nambu-Goldstone bosons in deconstructed Higgsless models. Using the (KK) Equivalence Theorem in 4D (5D), we derive a set of general sum rules among the boson masses and multi-boson couplings that are valid for arbitrary deconstructed models. Taking the continuum limit, our results naturally include the 5D Higgsless model sum rules for arbitrary 5D geometry and boundary conditions; they also reduce to the elastic sum rules when applied to the special case of elastic scattering. For the case of linear deconstructed Higgsless models, we demonstrate that the sum rules can also be derived from a set of general deconstruction identities and completeness relations. We apply these sum rules to the deconstructed 3-site Higgsless model and its extensions; we show that in 5D ignoring all higher KK modes (n>1) is inconsistent once the inelastic channels become important. Finally, we discuss how our results generalize beyond the case of linear Higgsless models.Comment: 36 pages, 2 figure

Deconstruction and Elastic pi pi Scattering in Higgsless Models

We study elastic pion-pion scattering in global linear moose models and apply the results to a variety of Higgsless models in flat and AdS space using the Equivalence Theorem. In order to connect the global moose to Higgsless models, we first introduce a block-spin transformation which corresponds, in the continuum, to the freedom to perform coordinate transformations in the Higgsless model. We show that it is possible to make an "f-flat" deconstruction in which all of the f-constants f_j of the linear moose model are identical; the phenomenologically relevant f-flat models are those in which the coupling constants of the groups at either end of the moose are small - corresponding to the global linear moose. In studying pion-pion scattering, we derive various sum rules, including one analogous to the KSRF relation, and use them in evaluating the low-energy and high-energy forms of the leading elastic partial wave scattering amplitudes. We obtain elastic unitarity bounds as a function of the mass of the lightest KK mode and discuss their physical significance.Comment: 33 pages, JHEP3. Minor typos correcte

Electroweak Corrections and Unitarity in Linear Moose Models

We calculate the form of the corrections to the electroweak interactions in the class of Higgsless models which can be "deconstructed'' to a chain of SU(2) gauge groups adjacent to a chain of U(1) gauge groups, and with the fermions coupled to any single SU(2) group and to any single U(1) group along the chain. The primary advantage of our technique is that the size of corrections to electroweak processes can be directly related to the spectrum of vector bosons ("KK modes"). In Higgsless models, this spectrum is constrained by unitarity. Our methods also allow for arbitrary background 5-D geometry, spatially dependent gauge-couplings, and brane kinetic energy terms. We find that, due to the size of corrections to electroweak processes in any unitary theory, Higgsless models with localized fermions are disfavored by precision electroweak data. Although we stress our results as they apply to continuum Higgsless 5-D models, they apply to any linear moose model including those with only a few extra vector bosons. Our calculations of electroweak corrections also apply directly to the electroweak gauge sector of 5-D theories with a bulk scalar Higgs boson; the constraints arising from unitarity do not apply in this case.Comment: 50 pages, 11 eps figures, typos correcte