Phenomenology of a light gluon resonance in top-physics at Tevatron and LHC

We present a phenomenological analysis of the recent Tevatron results on the t (t) over bar forward-backward asymmetry and invariant-mass spectrum assuming a new contribution from an s-channel gluon resonance with a mass in the range from 700 to 2500GeV. In contrast to most of the previous works, this analysis shows that for masses below similar to 1TeV resonant New Physics could accommodate the experimental data. In general, we find that axial-like couplings are preferred for light and top quark couplings, and that only top quark couples strongly to New Physics. We find that composite model scenarios arise naturally from only phenomenological analyses of the experimental results. We show that our results are compatible with recent LHC limits in dijet and t (t) over bar production, and find some tension for large resonance mass similar to 2.5 TeV. We indicate as best observables for discriminating a relatively light new gluon a better resolution in CDF forward-backward asymmetry, as well as the t (t) over bar charge asymmetry and invariant-mass spectrum at the LHC.