Scalar-mediated tt̄ forward-backward asymmetry

A large forward-backward asymmetry in tt̄ production, for large invariant mass of the tt̄ system, has been recently observed by the CDF collaboration. Among the scalar mediated mechanisms that can explain such a large asymmetry, all colored representations are inconsistent by more than 2σ with at least one other top-related measurement. In contrast, the t-channel exchange of a color-singlet weak-doublet scalar is consistent with the differential and with the integrated tt̄ cross section measurements. Constraints from flavor changing processes dictate a very specific structure for the Yukawa couplings of such a new scalar. No sizable deviation in the differential or integrated tt̄ production cross section is expected at the LHC.