Tevatron Top Quark Forward-Backward Asymmetry -- Implications for\n Same-sign Top Quark Pair Production

The forward-backward asymmetry for top quarks measured in proton-antiproton\ncollisions at the Tevatron shows an interesting deviation from standard model\nexpectations. Among possible interpretations, the exchange of a non-universal,\nflavor-changing $Z^\\prime$ is of some interest as it naturally predicts a top\nquark in the forward region of rapidity. To reproduce the size of the Tevatron\nasymmetry, the couplings of the $Z^\\prime$ to standard model quarks must be\nlarge, inevitably leading to production of same-sign top quark pairs at the\nTevatron and at the Large Hadron Collider (LHC). We discuss the constraints on\nthis model from (a) the Tevatron $t \\bar{t}$ cross section, (b) the Tevatron $t\n\\bar{t}$ invariant mass distribution, and the limits at the Tevatron on the\nsame sign top quark pair cross section. We explore the discovery potential for\n$tt$ and $ttj$ production in early LHC experiments at 7 TeV and conclude that\nif a $tt$ signal is not observed with 1 fb$^{-1}$ of integrated luminosity,\nthen a non-universal $Z^\\prime$ alone cannot explain the Tevatron\nforward-backward asymmetry. Limits on the same sign cross section at the LHC\nfrom the CMS collaboration already disfavor this interpretation of the reported\nasymmetry.\n