2-LOOP O(G(F)M(H)(2)) RADIATIVE-CORRECTIONS TO THE HIGGS-BOSON DECAY WITH H-]GAMMA-GAMMA FOR LARGE HIGGS-BOSON MASSES

This paper is devoted to the calculation of the two-loop O(G(F)M(H)(2) ) radiative corrections to the Higgs boson decay width H --> gamma gam ma for large values of the Higgs boson mass M(H) within the minimal st andard model. The use of the equivalence theorem makes it possible to reduce the problem to the consideration of the physical Higgs boson fi eld and the Goldstone bosons w(+),w(-),z. We present analytical result s for the various two- and three-particle absorptive parts of the two- loop contributions, and, using dispersive techniques, analytic results for all but one of the dispersive contributions. The relative correct ions to the decay width are large because of strong cancellations betw een the W and top loops in the lowest order, but the absolute correcti ons are small and perturbatively under control.