Strengthening constraints on new physics from the B -> X_s gamma branching ratio requires improving accuracy in the measurements and the Standard Model predictions. To match the expected Belle-II accuracy, Next-to-Next-to-Leading Order (NNLO) QCD corrections must be calculated without the so-far employed interpolation in the charm-quark mass m_c. In the process of evaluating such corrections at the physical value of m_c, we have finalized the part coming from diagrams with closed fermion loops on the gluon lines that contribute to the interference of the current-current and photonic dipole operators. We confirm several published results for corrections of this type, and supplement them with a previously uncalculated piece. Taking into account the recently improved estimates of non-perturbative contributions, we find B_{s gamma} = (3.40 \pm 0.17) * 10^{-4} and R_gamma = B_{(s+d) gamma}/B_{c l nu} = (3.35 \pm 0.16) * 10^{-3} for E_gamma > 1.6 GeV in the decaying meson rest frame.

中文翻译：

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朝着 $$ \overline{B}\to {X}_s\gamma $$ 在 QCD 的 NNLO 处，没有在 mc 中插值

从 B -> X_s 伽马分支比加强对新物理学的约束需要提高测量和标准模型预测的准确性。为了与预期的 Belle-II 精度相匹配，必须在没有迄今为止在粲夸克质量 m_c 中采用的插值的情况下计算 Next-to-Next-to-Leading Order (NNLO) QCD 校正。在以 m_c 的物理值评估此类修正的过程中，我们最终确定了来自胶子线上闭合费米子环图的部分，这些图有助于电流-电流和光子偶极子算子的干扰。我们确认了一些已发布的此类更正结果，并用以前未计算的部分对其进行了补充。考虑到最近对非微扰贡献的改进估计，我们发现 B_{s gamma} = (3.40 \pm 0.