Top-pair forward-backward asymmetry from loops of new strongly coupled quarks

We examine loop-mediated effects of new heavy quarks Q = (t', b') on t (t) over bar production at hadron colliders, using a phenomenological model with flavor off-diagonal couplings of charged and neutral scalars phi = (phi(+/-); phi(0)) to Q. We show that an invariant-mass-dependent asymmetry, in the t (t) over bar center of mass, consistent with those recently reported by the CDF collaboration, can be obtained for quark masses around 350-500 GeV, scalar masses of order 100-200 GeV, and modest-to-strong Yukawa couplings. The requisite strong interactions suggest a nonperturbative electroweak-symmetry-breaking mechanism and composite states at the weak scale. A typical prediction of this framework is that the new heavy quarks decay dominantly into t phi final states.