Forward-backward asymmetry of top quark pair production

We adopt a Markov chain Monte Carlo method to examine various new physics models which can generate the forward-backward asymmetry in top quark pair production observed at the Tevatron by the CDF Collaboration. We study the following new physics models: (1) exotic gluon G', (2) extra Z' boson with flavor-conserving interaction, (3) extra Z' with flavor-violating u-t-Z' interaction, (4) extra W' with flavor-violating d-t-W' interaction, and (5) extra scalars S and S-+/- with flavor-violating u-t-S and d-t-S-+/- interactions. After combining the forward-backward asymmetry with the measurement of the top pair production cross section and the t (t) over bar invariant mass distribution at the Tevatron, we find that an axial vector exotic gluon G' of mass about 1 TeV or 2 TeV or a W' of mass about 2TeV offer an improvement over the standard model. The other models considered do not fit the data significantly better than the standard model. We also emphasize a few points that have been long ignored in the literature for new physics searches: (1) heavy resonance width effects, (2) renormalization scale dependence, and (3) next-to-leading order corrections to the t (t) over bar invariant mass spectrum. We argue that these three effects are crucial to test or exclude new physics effects in the top quark pair asymmetry.