Top quark forward-backward asymmetry from new<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>t</mml:mi></mml:math>-channel physics

Abstract

Motivated by recent measurements of the top quark forward-backward asymmetry at the Tevatron, we study how $t$-channel new physics can contribute to a large value. We concentrate on a theory with an Abelian gauge boson that possesses flavor changing couplings between up and top quarks but satisfies flavor physics constraints. Collider constraints are strong, but can be accommodated with the aid of small flavor-diagonal couplings. We find that ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\approx}160\text{ }\text{ }\mathrm{GeV}$ can yield a total lab-frame asymmetry of $\ensuremath{\sim}18%$ without conflicting with other observables. There are implications for future collider searches, including exotic top quark decays, like-sign top quark production, and detailed measurements of the top production cross section. An alternate model with a gauged non-Abelian flavor symmetry has similar phenomenology, but lacks the like-sign top signal.