Top quark forward-backward asymmetry from SU(N_c) color

TL;DR

This paper proposes that extending QCD to an SU(N_c) gauge group with N_c > 5 and a low symmetry-breaking scale can explain the top quark forward-backward asymmetry observed at the Tevatron, predicting new phenomena at the LHC.

Contribution

It introduces a novel SU(N_c) extension of QCD with spontaneous symmetry breaking near the TeV scale to explain the asymmetry, emphasizing radiative effects over tree-level contributions.

Findings

Extended gauge interactions amplify asymmetry effects.

Model consistent with current collider data.

Predicts new phenomena observable at the LHC.

Abstract

We argue that the $t \bar t$ production asymmetry observed at the tevatron might be simply explained if the standard $SU(3)_c$ QCD theory is extended to $SU(N_c)$ which is spontaneously broken at a scale just above the weak scale. The extended gauge interactions amplify the radiative QCD contribution to the asymmetry and can potentially explain the observations if $N_c \stackrel{>}{\sim} 5$. This explanation requires a relatively low $SU(N_c)$ symmetry breaking scale $\stackrel{<}{\sim} 0.5-1$ TeV. We check that such a low $SU(N_c)$ symmetry breaking scale is consistent with current collider data. Importantly this scenario predicts an abundance of striking phenomena which will be probed at the LHC. The $SU(N_c)$ model also illustrates the idea that a beyond standard model contribution to the $t \bar t$ asymmetry might arise primarily via radiative corrections rather than at tree-level.