Axigluons cannot explain the observed top quark forward-backward asymmetry

TL;DR

This paper critically examines an axigluon model proposed to explain the top quark forward-backward asymmetry, finding that experimental constraints and model extensions make it unlikely to be the cause of the observed asymmetry.

Contribution

The paper provides a comprehensive analysis showing that existing experimental data and model extensions exclude axigluons as the explanation for the top quark asymmetry.

Findings

B_d-meson mixing data excludes key parameter regions.

Large axigluon masses are constrained by gauge coupling limits.

Embedding in extra dimensions dilutes the axigluon effect.

Abstract

We study an SU(3)^2 axigluon model introduced by Frampton, Shu, and Wang to explain the recent Fermilab Tevatron observation of a significant positive enhancement in the top quark forward-backward asymmetry relative to standard model predictions. First, we demonstrate that data on neutral B_d-meson mixing excludes the region of model parameter space where the top asymmetry is predicted to be the largest. Keeping the gauge couplings below the critical value that would lead to fermion condensation imposes further limits at large axigluon mass, while precision electroweak constraints on the model are relatively mild. Furthermore, by considering an extension to an SU(3)^3 color group, we demonstrate that embedding the model in an extra-dimensional framework can only dilute the axigluon effect on the forward-backward asymmetry. We conclude that axigluon models are unlikely to be the source of the observed top quark asymmetry.