Top-quark pair production at next-to-next-to-leading order QCD in   electron positron collisions
  We set up a formalism, within the antenna subtraction framework, for computing the production of a massive quark-antiquark pair in electron positron collisions at next-to-next-to-leading order in the coupling $\alpha_s$ of quantum chromodynamics at the differential level. Our formalism applies to the calculation of any infrared-safe observable. We apply this set-up to the production of top-quark top antiquark pairs in the continuum. We compute the production cross section and several distributions. We determine, in particular, the top-quark forward-backward asymmetry at order $\alpha_s^2$. Our result agrees with previous computations of this observable. 
Long Chen, Oliver Dekkers, Dennis Heisler, Werner Bernreuther,   Zong-Guo Si
hep-ph hep-ex