Explaining the t-tbar asymmetry with a light axigluon

TL;DR

This paper introduces a light axigluon model to explain the Tevatron t-tbar asymmetry, predicting specific asymmetry behaviors and suggesting UV completions with new particles that could be tested at colliders.

Contribution

It proposes a flavor universal light axigluon with specific couplings and mass range to account for the asymmetry, including UV completions with new colored particles.

Findings

Axigluon explains the asymmetry via interference effects.

Predicted asymmetry changes sign around 450 GeV.

UV completions imply new multi-jet signatures at colliders.

Abstract

We propose an axigluon with mass between 400 and 450 GeV and flavor universal couplings to quarks to explain the Tevatron t-tbar forward-backward asymmetry. The model predicts a small negative asymmetry for t-tbar pairs with invariant mass below 450 GeV and a large positive asymmetry above 450 GeV. The asymmetry arises from interference between s-channel gluon and axigluon diagrams and requires a relatively weakly coupled axigluon ($g_{a} = g_{qcd}/3$). Axigluon-gluon interference does not contribute to the t-tbar cross section. New contributions to the cross section arise only at fourth order in the axigluon coupling and are very small for a sufficiently broad axigluon. Dijet measurements do not significantly constrain the axigluon couplings. We propose several possible UV completions of the phenomenological axigluon which explain the required small couplings and large width. Such UV completions necessarily contain new colored fermions or scalars below the axigluon mass and predict multi-jet events with large cross sections at the Tevatron and LHC.