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 tbar 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 tbar 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 non-perturbative 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. 
Hooman Davoudiasl, Thomas McElmurry, Amarjit Soni
hep-ph hep-ex