Decays A → Zγγ and φ → Zγγ (φ = h, H) in two-Higgs doublet models

The one-loop contributions to the decays of the CP-odd and CP-even scalar bosons A -> Z gamma gamma and phi -> Z gamma gamma (phi = h, H) are calculated within the framework of CP-conserving two-Higgs doublet models (THDMs), where they are induced by box and reducible Feynman diagrams. The behavior of the corresponding branching ratios are then analyzed within the type-II THDM in a region of the parameter space around the alignment limit and still consistent with experimental data. It is found that the A -> Z gamma gamma branching ratio is only relevant when m(A) > m(H) thorn m(Z), but it is negligible otherwise. For m(A) > 600 GeV and t(beta) similar or equal to O(1), BRoA -> Z gamma gamma) can reach values of the order of 10(-5) - 10(-4), but it decreases by about 1 order of magnitude as t(beta) increases up to 10. A similar behavior is followed by the H -> Z gamma gamma decay, which only has a non-negligible branching ratio when m(H) > m(A) thorn mZ and can reach the level of 10(-4) - 10(-3) for m(H) > 600 GeV and t(beta) similar or equal to O(1). We also estimated the branching ratios of these rare decays in the type-I THDM, where they can be about 1 order of magnitude larger than in type-II THDM. As far as the h -> Z gamma gamma decay is concerned, since the properties of this scalar boson must be nearly identical to those of the SM Higgs boson, the h -> Z gamma gamma branching ratio does not deviate significantly from the SM prediction, where it is negligibly small, of the order of 10(-9). This result is in agreement with previous calculations.