Weakly coupled Higgsless theories and precision electroweak tests

TL;DR

This work analyzes weakly coupled Higgsless theories realized as five-dimensional gauge theories with electroweak breaking by boundary conditions. Using a calculable model with gauged custodial symmetry and boundary terms, it evaluates oblique corrections, focusing on the $\epsilon_3$ (or $S$) parameter. It shows that, in the calculable regime, $\epsilon_3$ is generically positive and large unless one introduces problematic boundary terms that generate ghosts, implying no simultaneous gain in perturbativity and EWPT compatibility. The study connects the 5D setup to holographic technicolor/large-$N$ pictures and concludes that the anticipated improvements are unlikely to be achieved, highlighting enduring tensions between Higgsless mechanisms and precision data.

Abstract

In 5 dimensions the electroweak symmetry can be broken by boundary conditions, leading to a new type of Higgsless theories. These could in principle improve on the 4D case by extending the perturbative domain to energies higher than $4 πv$ and by allowing a better fit to the electroweak precision tests. Nevertheless, it is unlikely that both these improvements can be achieved, as we show by discussing these problems in an explicit model.