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

TL;DR

This paper calculates the dominant two-loop electroweak corrections to the couplings of the CP-odd Higgs boson to photons and gluons in a two-Higgs-doublet model, including effects of a potential fourth fermion generation.

Contribution

It provides the first detailed computation of two-loop electroweak corrections to A^0 couplings in this model, considering heavy fermion effects and gamma_5 regularisation issues.

Findings

Two-loop corrections significantly affect A^0 couplings.

The finite renormalisation constant for the pseudoscalar current remains uncorrected at this order.

Reassessment of the H -> gamma gamma decay width with a fourth fermion generation.

Abstract

Using the asymptotic-expansion technique, we compute the dominant two-loop electroweak corrections, of O(G_F m_t^2), to production and decay via a pair of photons or gluons of the CP-odd Higgs boson A^0 in a two-Higgs-doublet model with low- to intermediate values of the Higgs-boson masses and ratio tan(beta)=v_2/v_1 of the vacuum expectation values. We also study the influence of a sequential heavy-fermion generation. The appearance of three gamma_5 matrices in closed fermion loops requires special care in the dimensional regularisation of ultraviolet divergences. The finite renormalisation constant for the pseudoscalar current effectively restoring the anticommutativity of the gamma_5 matrix, familiar from perturbative quantum chromodynamics, is found not to receive a correction in this order. We also revisit the dominant two-loop electroweak correction to the H -> gamma gamma decay width in the standard model with a fourth fermion generation.