$Z'$ Phenomenology: A Model-independent Analysis and Fit in Combination of Chiral Effective Theory and Anomaly Cancellation

TL;DR

This paper develops a model-independent framework combining chiral effective theory and anomaly cancellation to analyze $Z'$ phenomenology, focusing on mixings, anomaly constraints, and electroweak precision fits.

Contribution

It introduces a novel, model-independent approach to $Z'$ analysis using anomaly cancellation and effective theory, linking charge assignments with Stueckelberg couplings and performing global fits.

Findings

Mixing parameters are of order 10^{-3}.

The analysis yields a negative contribution to the $S$ parameter.

The anomaly cancellation constrains the number of right-handed neutrinos.

Abstract

To investigate $Z'$ phenomenology model-independent, we combine chiral effective theory with anomaly cancellation conditions without any other model input. We focus on $Z'$ mixings with $\gamma-Z$ in both mass and kinetic parts and calculate contributions to oblique $S,T,U$. The three sets of anomaly-free fermion $U(1)'$ charges parameterize the $Z'$ interactions with fermions. The cancellation of the $[U(1)']^3$ anomaly and mixing gravitational-gauge anomaly determines the number of right-handed neutrinos. We also find a novel relation between the charge assignments and Stueckelberg coupling in terms of the renormalized electromagnetic current. A global fit to the electroweak precise observables shows that typical values for the mixing parameters are of order $10^{-3}$. In spite of this strict limit, we obtain a negative $S$ parameter contribution.