  In this work, we review and clarify computational issues about the W-gauge
boson one-loop contribution to the H -> gamma gamma decay amplitude, in the
unitary gauge and in the Standard Model. We find that highly divergent
integrals depend upon the choice of shifting momenta with arbitrary vectors.
One particular combination of these arbitrary vectors reduces the superficial
divergency down to a logarithmic one. The remaining ambiguity is then fixed by
exploiting gauge invariance and the Goldstone Boson Equivalence Theorem. Our
method is strictly realised in four-dimensions. The result for the amplitude
agrees with the "famous" one obtained using dimensional regularisation (DR) in
the limit d-> 4, where d is the number of spatial dimensions in Euclidean
space. At the exact equality d=4, a three-sphere surface term appears that
renders the Ward Identities and the equivalence theorem inconsistent. We also
examined a recently proposed four-dimensional regularisation scheme and found
agreement with the DR outcome.
