Heavy Higgs-boson lifetime at two loops

The standard-model Higgs boson with a mass {ital M}{sub {ital H}}{gt}2{ital M}{sub {ital Z}} decays almost exclusively to pairs of {ital W} and {ital Z} bosons. We calculate the dominant two-loop corrections, of {ital O}({ital G}{sup 2}{sub {ital F}}{ital M}{sup 4}{sub {ital H}}), to the partial widths of these decays. In the on-mass-shell renormalization scheme, the correction factor is found to be 1+14.6{percent}({ital M}{sub {ital H}}/TeV){sup 2}+16.9{percent}({ital M}{sub {ital H}}/TeV){sup 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. {copyright} {ital 1996 The American Physical Society.}