Virtual corrections to Higgs boson pair production in the large top quark mass limit

We calculate the three-loop matching coefficient C_HH, required for a consistent description of Higgs boson pair production in gluon fusion through next-to-next-to-leading order QCD in the heavy top quark approximation. We also compute the gg→HH amplitude in m_t→∞ approximation in the full theory and show its consistency with an earlier computation in heavy-top effective theory