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Using the asymptotic-expansion technique, we compute the dominant two-loopelectroweak corrections, of O(G_F m_t^2), to production and decay via a pair ofphotons or gluons of the CP-odd Higgs boson A^0 in a two-Higgs-doublet modelwith low- to intermediate values of the Higgs-boson masses and ratiotan(beta)=v_2/v_1 of the vacuum expectation values. We also study the influenceof a sequential heavy-fermion generation. The appearance of three gamma_5matrices in closed fermion loops requires special care in the dimensionalregularisation of ultraviolet divergences. The finite renormalisation constantfor the pseudoscalar current effectively restoring the anticommutativity of thegamma_5 matrix, familiar from perturbative quantum chromodynamics, is found notto receive a correction in this order. We also revisit the dominant two-loopelectroweak correction to the H -> gamma gamma decay width in the standardmodel with a fourth fermion generation.

Two-Loop Electroweak Corrections to the A^0 gamma gamma and A^0 g g Couplings of the CP-Odd Higgs Boson