One-loop Corrections to the S Parameter in the Four-site Model

TL;DR

This paper calculates one-loop corrections to the S parameter in a four-site Higgsless model, revealing that fermion delocalization does not sufficiently reduce large contributions to S, which remain problematic at one-loop level.

Contribution

It provides the first detailed computation of one-loop chiral-logarithmic corrections to the S parameter in the four-site Higgsless model, highlighting the need for fine-tuning.

Findings

One-loop corrections to S are significant and not mitigated by fermion delocalization.

Fermion delocalization parameter requires substantial tuning to satisfy experimental constraints.

Large one-loop contributions to S persist, challenging the viability of the model.

Abstract

We compute the leading chiral-logarithmic corrections to the S parameter in the four-site Higgsless model. In addition to the usual electroweak gauge bosons of the Standard Model, this model contains two sets of heavy charged and neutral gauge bosons. In the continuum limit, the latter gauge bosons can be identified with the first excited Kaluza-Klein states of the W^\pm and Z bosons of a warped extra-dimensional model with an SU(2)_L \times SU(2)_R \times U(1)_X bulk gauge symmetry. We consider delocalized fermions and show that the delocalization parameter must be considerably tuned from its tree-level ideal value in order to reconcile experimental constraints with the one-loop results. Hence, the delocalization of fermions does not solve the problem of large contributions to the S parameter in this class of theories and significant contributions to S can potentially occur at one-loop.