  We present the first complete calculation performed within the Four
Dimensional Regularization scheme (FDR), namely the loop-induced on-shell
amplitude for the Higgs boson decay into two photons in an arbitrary R_csi
gauge. FDR is a new technique -free of infinities- for addressing multi-loop
calculus, which automatically preserves gauge invariance, allowing for a
4-dimensional computation at the same time. We obtained the same result as that
assessed in dimensional regularization, thereby explicitly verifying, in a
realistic case, that FDR respects gauge invariance.
