The Top Forward Backward Asymmetry with general Z ' couplings

The measurement of the top forward-backward asymmetry in $\text{ttbar}$ production measured at the Tevatron shows deviation from the Standard Model prediction. A $u\to t$ transition via a flavor changing $Z^{\mathrm{\prime }}$ can explain the data. We show that left handed $t_L{u}_L{Z}^{\mathrm{\prime }}$ couplings can be constrained from $B_{d,s}$ mixing while the constrains on the right handed couplings $t_R u_R Z^{\prime}$vanishinthelimitof$m_u \to 0$. We then consider the most general form of the $tu{Z}^{\mathrm{\prime }}$ interaction which includes vector-axial vector as well as tensor type couplings and study how these couplings affect the top forward-backward asymmetry.