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Register a new userFlavor Structure of the Three Site Higgsless Model
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We study the flavor structure in the three site Higgsless model. In this model, the gauge bosons and fermions have heavy partners, coming from the Kaluza-Klein excitation in the dimensional deconstruction picture. The yukawa couplings are introduced in a way to minimize the flavor chaning neutral current in the light sector at the tree level. Due to the flavor mixing between the light and the heavy partner fields, new effects on FCNCs appear at one-loop level. As an example of such FCNC processes, we calculate the contribution to the b -> s gamma amplitude in the three site Higgsless model. Interestingly, heavy particles which exist in the three site Higgsless model do not completely decouple in the heavy-mass limit. One-loop level b -> s gamma amplitude is calculated by considering all possible combinations of particles in the loop, then it is compared to the experiment. The result shows that the central value of the B -> X_s gamma branching ratio in the three site Higgsless model takes closer value to its experimental central value as one takes the larger value of a free parameter, varepsilon_{tR}, within a range allowed by the precision electroweak measurement.
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We analyze the spectrum and properties of a highly-deconstructed Higgsless model with only three sites. Such a model contains sufficient complexity to incorporate interesting physics issues related to fermion masses and electroweak observables, yet remains simple enough that it could be encoded in a Matrix Element Generator program for use with Monte Carlo simulations. The gauge sector of this model is equivalent to that of the BESS model; the new physics of interest here lies in the fermion sector. We analyze the form of the fermion Yukawa couplings required to produce the ideal fermion delocalization that causes tree-level precision electroweak corrections to vanish. We discuss the size of one-loop corrections to b to s gamma, the weak-isospin violating parameter alpha T and the decay Z to b bar{b}. We find that the new fermiophobic vector states (the analogs of the gauge-boson KK modes in a continuum model) can be reasonably light, with a mass as low as 380 GeV, while the extra (approximately vectorial) quark and lepton states (the analogs of the fermion KK modes) must be heavier than 1.8 TeV.
We complete the list of one loop renormalization group equations and matching conditions relevant for the computation of the electroweak precision parameters $S$ and $T$ in the three site Higgsless model. We obtain one-loop formulas for $S$ and $T$ expressed in terms of physical observables such as the KK gauge boson mass $M_{W}$, the KK fermion mass $M$, and the KK gauge boson ($W$) couplings with light quarks and leptons $g_{Wff}$. It is shown that these physical observables, $M_{W}$, $M$ and $g_{Wff}$ are severely constrained by the electroweak precision data. Unlike the tree level analysis on the ideally delocalized fermion, we find that perfect fermiophobity of $W$ is ruled out by the precision data. We also study the cutoff dependence of our analysis. Although the model is non-renormalizable, the dependence on the cutoff parameter $Lambda$ is shown to be non-significant.
We consider the four-site Higgsless model, which predicts the existence of four charged and two neutral extra gauge bosons, $W_{1,2}^pm$ and $Z_{1,2}$. In contrast to other Higgsless models, characterized by fermiophobic extra gauge bosons, here sizeable fermion-boson couplings are allowed by the electroweak precision data. We thus analyse the prospects of detecting the new predicted particles in the mostly favored Drell-Yan channel at the LHC.
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.
We study the phenomenology of the neutral gauge sector of the four-site Higgsless model, based on the SU(2)_L x SU(2)_1 x SU(2)_2 x U(1)_Y gauge symmetry, at present colliders. The model predicts the existence of two neutral and four charged extra gauge bosons, Z_{1,2} and W^pm_{1,2}. We expand and update a previous study, by concentrating on the neutral sector. We derive new limits on Z_{1,2}-boson masses and couplings from recent direct searches at the Tevatron. We moreover estimate the discovery potential at the Tevatron with a project luminosity L=10 fb^{-1}, and at the 7 TeV LHC with L=1 fb^{-1}. In contrast to other Higgsless theories characterized by almost fermiophobic extra gauge bosons, the four-site model allows sizeable Z_{1,2}-boson couplings to SM fermions. Owing to this feature, we find that in the next two years the extra Z_{1,2}-bosons could be discovered in the favoured Drell-Yan channel at the 7 TeV LHC for Z_{1,2} masses in the TeV region, depending on model parameters.
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