Two-loop QCD corrections to Higgs-pair production at the LHC
  The calculation of the next-to-leading order QCD corrections to the production of a neutral Higgs-boson pair is briefly summarized. The dominant production mechanism is gluon fusion via top-quark loops, so that the QCD corrections can be considered, to good approximation, in the limit of a heavy top-quark mass. 
S.Dawson, S.Dittmaier and M.Spira