Next-to-next-to-leading order ${\cal O}(\alpha_s^4)$ results for heavy   quark pair production in quark--antiquark collisions: The one-loop squared   contributions
  We calculate the next-to-next-to-leading order ${\cal O}(\alpha_s^4)$ one-loop squared corrections to the production of heavy quark pairs in quark-antiquark annihilations. These are part of the next-to-next-to-leading order ${\cal O}(\alpha_s^4)$ radiative QCD corrections to this process. Our results, with the full mass dependence retained, are presented in a closed and very compact form, in the dimensional regularization scheme. We have found very intriguing factorization properties for the finite part of the amplitudes. 
J. G. K\"orner, Z. Merebashvili and M. Rogal