Dominant two-loop electroweak corrections to the hadroproduction of a pseudoscalar Higgs boson and its photonic decay

We present the dominant two-loop electroweak corrections to the partial decay widths to gluon jets and prompt photons of the neutral CP-odd Higgs boson A(0), with mass M-A(0) < 2M(W), in the two-Higgs-doublet model for low to intermediate values of the ratio tan beta = v(2)/v(1) of the vacuum expectation values. They apply as they stand to the production cross sections in hadronic and two-photon collisions, at the Tevatron, the LHC, and a future photon collider. The appearance of three gamma(5) matrices in closed fermion loops requires special care in the dimensional regularization of ultraviolet divergences, and the finite electroweak renormalization of the pseudoscalar current restoring the anticommutativity of gamma(5) is performed for the first time. The corrections are negative and amount to several percent, so that they fully compensate or partly screen the enhancement due to QCD corrections.