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Register a new userMulti-Gauge-Boson Vertices and Chiral Lagrangian Parameters in Higgsless Models with Ideal Fermion Delocalization
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Higgsless models with fermions whose SU(2) properties are ideally delocalized, such that the fermions 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.
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In this note we examine the properties of deconstructed Higgsless models for the case of a fermion whose SU(2) properties arise from delocalization over many sites of the deconstructed lattice. We derive expressions for the correlation functions and use these to establish a generalized consistency relation among correlation functions. We discuss the form of the W boson wavefunction and show that if the probability distribution of the delocalized fermions is appropriately related to the W wavefunction, then deviations in precision electroweak parameters are minimized. In particular, we show that this ideal fermion delocalization results in the vanishing of three of the four leading zero-momentum electroweak parameters defined by Barbieri, et. al. We then discuss ideal fermion delocalization in the context of two continuum Higgsless models, one in Anti-deSitter space and one in flat space. Our results may be applied to any Higgsless linear moose model with multiple SU(2) groups, including those with only a few extra vector bosons.
We discuss ideal delocalization of fermions in a bulk SU(2) x SU(2) x U(1) Higgsless model with a flat or warped extra dimension. So as to make an extra dimensional interpretation possible, both the weak and hypercharge properties of the fermions are delocalized, with the U(1)_Y current of left-handed fermions being correlated with the SU(2)_W current. We find that (to subleading order) ideal fermion delocalization yields vanishing precision electroweak corrections in this continuum model, as found in corresponding theory space models based on deconstruction. In addition to explicit calculations, we present an intuitive argument for our results based on Georgis spring analogy. We also discuss the conditions under which the essential features of an SU(2) x SU(2) x U(1) bulk gauge theory can be captured by a simpler SU(2) x SU(2) model.
Recently, Higgsless models have proven to be viable alternatives to the Standard Model (SM) and supersymmetric models in describing the breaking of the electroweak symmetry. Whether extra-dimensional in nature or their deconstructed counterparts, the physical spectrum of these models typically consists of ``towers of massive vector gauge bosons which carry the same quantum numbers as the SM W and Z. In this paper, we calculate the one-loop, chiral-logarithmic corrections to the S and T parameters from the lightest (i.e. SM) and the next-to-lightest gauge bosons using a novel application of the Pinch Technique. We perform our calculation using generic Feynman rules with generic couplings such that our results can be applied to various models. To demonstrate how to use our results, we calculate the leading chiral-logarithmic corrections to the S and T parameters in the deconstructed three site Higgsless model. As we point out, however, our results are not exclusive to Higgsless models and may, in fact, be used to calculate the one-loop corrections from additional gauge bosons in models with fundamental (or composite) Higgs bosons.
In this note we compute the flavor-dependent chiral-logarithmic corrections to the decay Z to b bbar in the three site Higgsless model. We compute these corrections diagrammatically in the gaugeless limit in which the electroweak couplings vanish. We also compute the chiral-logarithmic corrections to the decay Z to b bbar using an RGE analysis in effective field theory, and show that the results agree. In the process of this computation, we compute the form of the chiral current in the gaugeless limit of the three-site model, and consider the generalization to the N-site case. We elucidate the Ward-Takahashi identities which underlie the gaugeless limit calculation in the three-site model, and describe how the result for the Z to b bbar amplitude is obtained in unitary gauge in the full theory. We find that the phenomenological constraints on the three-site Higgsless model arising from measurements of Z to b bbar are relatively mild, requiring only that the heavy Dirac fermion be heavier than 1 TeV or so, and are satisfied automatically in the range of parameters allowed by other precision electroweak data.
Non-decoupling effects of heavy particles present in beyond-the-standard models are studied for the triple gauge boson vertices $gamma W^+W^-$ and $Z^0W^+W^-$. We show from a general argument that the non-decoupling effects are described by four independent parameters, in comparison with the three parameters $S$, $T$ and $U$ in the oblique corrections. These four parameters of the effective triple gauge boson vertices are computed in two beyond-the-standard models. We also study the relation of the four parameters to the $S$, $T$, $U$ parameters, relying on an operator analysis.
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