Effective axial-vector coupling of gluon as an explanation to the top quark asymmetry

TL;DR

This paper proposes that an effective axial-vector coupling of gluons could explain the Tevatron top quark forward-backward asymmetry, providing a model-independent, testable alternative to new physics scenarios.

Contribution

It introduces a universal effective axial-vector gluon coupling at 1-loop level that accounts for the asymmetry without conflicting with LHC constraints.

Findings

The coupling naturally induces the observed asymmetry growth with invariant mass.

It is consistent with existing cross section measurements.

Predicts energy-dependent top quark polarization effects.

Abstract

We explore the possibility that the large $t\bar t$ forward-backward asymmetry measured by the CDF detector at Tevatron could be due to a universal effective axial-vector coupling of gluon. Using an effective field theory approach we show model independently how such a log-enhanced coupling occurs at 1-loop level. The interference with QCD gluon vector coupling naturally induces the observed positive forward-backward $t\bar t$ asymmetry that grows with $t\bar t$ invariant mass and is consistent with the cross section measurements. This scenario does not involve new flavor changing couplings nor operators that interfere with QCD, and, therefore, is not constrained by the LHC searches for 4-quark contact interactions. We predict top quark polarization effects that grow with energy and allow to test this scenario at the LHC. Our proposal offers a viable alternative to new physics scenarios that explain the $t\bar t$ forward-backward asymmetry anomaly with the interference between QCD and tree level new physics amplitudes.