We analyze the Nelson-Barr approach to the Strong CP Problem. We derive the necessary conditions in order to simultaneously reproduce the CKM phase and the quark masses. Then we quantify the irreducible contributions to the QCD topological angle, namely the corrections arising from loops of the colored fermion mediators that characterize these models. Corrections analytic in the couplings first arise at 3-loop order and are safely below current bounds; non-analytic effects are 2-loop order and decouple as the mediators exceed a few TeV. We discuss collider, electroweak, and flavor bounds and argue that most of the parameter space above the TeV scale is still allowed in models with down-type mediators, whereas other scenarios are more severely constrained. With two or more families of mediators the dominant experimental bound is due to the neutron electric dipole moment.

我们分析了强 CP 问题的 Nelson-Barr 方法。我们推导出了同时再现 CKM 相和夸克质量的必要条件。然后我们量化对 QCD 拓扑角的不可约贡献，即由表征这些模型的有色费米子介体的回路引起的校正。耦合中的校正分析首先出现在 3 环阶并且安全地低于电流界限；非解析效应是 2 环阶的，并且在介体超过几个 TeV 时解耦。我们讨论了对撞机、电弱和风味界限，并认为在具有向下型介体的模型中仍然允许超过 TeV 尺度的大部分参数空间，而其他场景则受到更严格的限制。