The decay of the Higgs particle into two photons through a [Formula: see text] loop was calculated in a straightforward way four years ago on the basis of the standard model. This calculation was carried out in the unitary gauge. Nevertheless, all attempts to reproduce this correct answer using the Feynman rules in the [Formula: see text] gauge, or the more general [Formula: see text] gauge, have failed. In this paper, a detailed analysis is carried out to compare the unitary gauge with the [Formula: see text] gauge; through this comparison, the underlying reason is determined why the answer cannot be obtained using the Feynman rules in the [Formula: see text] gauge. This is the first example where the use of the Feynman rules in the [Formula: see text] gauge leads to an incorrect answer, and this incorrect answer cannot be ruled out by any simple argument such as gauge invariance. It means that great care must be exercised in using Feynman rules.
Feynman rules for the rational part of the standard model one-loop amplitudes in the ’t Hooft-Veltman γ 5 scheme
