On the two-loop virtual QCD corrections to Higgs boson pair production in the standard model

We compute the next-to-leading order virtual QCD corrections to Higgs-pair production via gluon fusion. We present analytic results for the two-loop contributions to the spin-0 and spin-2 form factors in the amplitude. The reducible contributions, given by the double-triangle diagrams, are evaluated exactly while the two-loop irreducible diagrams are evaluated by an asymptotic expansion in heavy top-quark mass up to and including terms of O(1/mt8). Assuming that the finite top-quark mass effects are of similar size in the entire range of partonic energies, we estimate that mass effects can reduce the hadronic cross section by at most 10%.