One-loop corrections to the S and T parameters in a three site Higgsless model

In this paper we compute 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 ρ± and ρ0), rather than an infinite tower of Kaluza-Klein modes. We compute the corrections to S and T in 't Hooft-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 ρ 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 ρ 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 ''nondecoupling'' contributions present in the limit Mρ→∞