Structure of corrections to electroweak interactions in Higgsless models

Abstract

Recently, Higgsless models of electroweak symmetry breaking have been proposed. Based on compactified five-dimensional gauge theories, these models achieve unitarity of electroweak boson self-interactions through the exchange of a tower of massive vector bosons rather than the exchange of a scalar Higgs boson. In this paper, using deconstruction, we analyze the form of the corrections to the electroweak interactions in a large class of these models, allowing for arbitrary 5-D geometry, position-dependent gauge coupling, and brane kinetic-energy terms. We show that 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, $S\ensuremath{-}4{cos}^{2}{\ensuremath{\theta}}_{W}T>\mathcal{O}(1)$, where $S$ and $T$ are the usual oblique parameters. We concur with the result of Cacciapaglia et al. that small or negative $S$ is possible---though only at the expense of substantial negative $T$ at tree level. Although we stress our results as they apply to continuum 5-D models, they apply also to models of extended electroweak gauge symmetries motivated by models of hidden local symmetry.