Heavy Higgs-boson lifetime at two loops

The standard-model Higgs boson with a mass $M_H\gg 2M_Z$ decays almost exclusively to pairs of $W$ and $Z$ bosons. We calculate the dominant two-loop corrections, of $O\left(G_F^2{M}_H^4\right)$, to the partial widths of these decays. In the on-mass-shell renormalization scheme, the correction factor is found to be $1+14.6\%{(M_H/\mathrm{TeV})}^2+16.9\%{(M_H/\mathrm{TeV})}^4$, where the second term is the one-loop correction. We give full analytic results for all divergent two-loop Feynman diagrams. A subset of finite two-loop vertex diagrams is computed to high precision using numerical techniques. We find agreement with a previous numerical analysis. The above correction factor is also in line with a recent lattice calculation.