Production of two Z-bosons in gluon fusion in the heavy top quark approximation

We compute QCD radiative corrections to the continuum production of a pair of Z  -bosons in the annihilation of two gluons. We only consider the contribution of the top quark loops and we treat them assuming that mtmt is much larger than any other kinematic invariant in the problem. We estimate the QCD corrections to pp→ZZpp→ZZ using the first non-trivial term in the expansion in the inverse top quark mass and we compare them to QCD corrections of the signal process, pp→H→ZZpp→H→ZZ.