Dispersion theoretic calculation of the $H\rightarrow Z+\gamma$ amplitude

We have calculated the W-loop contribution to the amplitude of the decay H -> Z + gamma in two different methods: (1) in the R xi-gauge using dimensional regularization (DimReg), and (2) in the unitary gauge through the dispersion method. Using the dispersion method we have followed two approaches: (i) without subtraction and (ii) with subtraction, the subtraction constant being determined adopting the Goldstone boson equivalence theorem (GBET) at the limit M-w -> 0. The results of the calculations in fib-gauge with DimReg and the dispersion method with the GBET completely coincide, which shows that DimReg is compatible with the dispersion method obeying the GBET.