Higgsless Electroweak Symmetry Breaking in Warped Backgrounds: Constraints and Signatures

TL;DR

This work investigates a Higgsless electroweak symmetry breaking framework in a warped 5D bulk with gauge group $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$, implementing EWSB via boundary conditions and incorporating brane-localized kinetic terms and curvature effects. The authors show that precision electroweak data can be accommodated for large $\kappa$ values (roughly $\kappa\gtrsim 3$), but perturbative unitarity in $W_L^+W_L^-$ scattering is violated around $\sqrt{s}\sim 2$ TeV across the parameter space, implying the model is not perturbatively reliable without new dynamics. Collider analyses predict observable spin-1 KK gauge bosons and KK gluons at the LHC, with two nearly degenerate $Z$-type KK states providing distinctive resonance structures; however, spin-2 graviton KK resonances are too weakly coupled to be detected in standard channels. The study highlights a tension between EW data compatibility and unitarity, suggesting that a UV-complete extension with additional non-Higgs states is necessary, while the AdS/CFT interpretation motivates exploring 4D strongly coupled duals to realize a fully consistent theory.

Abstract

We examine the phenomenology of a warped 5-dimensional model based on SU(2)$_L \times$ SU(2)$_R \times$ U(1)$_{B-L}$ model which implements electroweak symmetry breaking through boundary conditions, without the presence of a Higgs boson. We use precision electroweak data to constrain the general parameter space of this model. Our analysis includes independent $L$ and $R$ gauge couplings, radiatively induced UV boundary gauge kinetic terms, and all higher order corrections from the curvature of the 5-d space. We show that this setup can be brought into good agreement with the precision electroweak data for typical values of the parameters. However, we find that the entire range of model parameters leads to violation of perturbative unitarity in gauge boson scattering and hence this model is not a reliable perturbative framework. Assuming that unitarity can be restored in a modified version of this scenario, we consider the collider signatures. It is found that new spin-1 states will be observed at the LHC and measurement of their properties would identify this model. However, the spin-2 graviton Kaluza-Klein resonances, which are a hallmark of the Randall-Sundrum model, are too weakly coupled to be detected.