On the two-loop virtual QCD corrections to Higgs boson pair production in the standard model Giuseppe Degrassi, Pier Paolo Giardino and Ramona Gröber Eur. Phys. J. C, 76 7 (2016) 411 Published online: 21 July 2016 DOI: 10.1140/epjc/s10052-016-4256-9