Z to b bbar and Chiral Currents in Higgsless Models

TL;DR

This paper calculates flavor-dependent chiral-logarithmic corrections to Z to b bbar decay in the three-site Higgsless model using diagrammatic and RGE methods, finding mild phenomenological constraints on model parameters.

Contribution

It provides a detailed computation of chiral-logarithmic corrections in Higgsless models and demonstrates their agreement across different methods, extending analysis to N-site models.

Findings

Corrections are small enough to satisfy experimental constraints.

Heavy fermions need to be heavier than about 1 TeV.

Results are consistent with other electroweak precision data.

Abstract

In this note we compute the flavor-dependent chiral-logarithmic corrections to the decay Z to b bbar in the three site Higgsless model. We compute these corrections diagrammatically in the "gaugeless" limit in which the electroweak couplings vanish. We also compute the chiral-logarithmic corrections to the decay Z to b bbar using an RGE analysis in effective field theory, and show that the results agree. In the process of this computation, we compute the form of the chiral current in the gaugeless limit of the three-site model, and consider the generalization to the N-site case. We elucidate the Ward-Takahashi identities which underlie the gaugeless limit calculation in the three-site model, and describe how the result for the Z to b bbar amplitude is obtained in unitary gauge in the full theory. We find that the phenomenological constraints on the three-site Higgsless model arising from measurements of Z to b bbar are relatively mild, requiring only that the heavy Dirac fermion be heavier than 1 TeV or so, and are satisfied automatically in the range of parameters allowed by other precision electroweak data.