Mass dependent top forward backward asymmetry in the effective Lagrangian approach: Addendum to "Model independent analysis of the forward-backward asymmetry of top quark production at the Tevatron"

Recently the CDF and the D0 Collaborations presented the data on the top forward-backward (FB) asymmetry A_FB as functions of M_(t t^bar) and \Delta y = y_t - y_t^bar. We study these observables in the effective Lagrangian approach with dimension-6 q q^bar t t^bar contact interactions, and compare with the CDF and D0 data. When we stay within the validity region of the effective Lagrangian approach, the mass dependent top FB asymmetry turns out to be smaller than the CDF data, more than 2-sigma away. If this discrepancy remains in the future data with better statistics, it would imply that the effective Lagrangian approach is not adequate for the top FB asymmetry, and a new physics scale around a few hundred GeV in the t- or u-channel may be responsible for the observed top FB asymmetry.