标题： 关于CP奇宇称π-核子耦合的确定 显示英文标题

标题： Towards the determination of CP-odd pion-nucleon couplings

摘要： 与夸克色磁偶极矩（cMDMs）相关的核子矩阵元（NMEs）在确定由夸克色电偶极矩诱导的CP奇异π-核子耦合中起着关键作用。 近年来，有人认为cMDMs的NMEs可以与核子高扭度（具体来说，扭曲三阶）部分子分布函数（PDF）$e(x)$的第三矩相关联，原则上可以通过半包容深弹性散射过程中的二介子产生来测量。 通过在大$N_c$极限下对cMDM算符应用自旋-味展开，其中$N_c$是夸克的颜色数，我们表明NMEs不仅受到扭曲三阶PDF$e(x)$的影响，还受到之前被忽略的核子形式因子的额外贡献。 结合自旋-味展开的约束、$e(x)$的近期实验数据以及$e(x)$的模型计算，我们估计了cMDM算符的NMEs。 我们的分析表明，NMEs主要由核子形式因子主导，cMDM对π-核子耦合的贡献可与夸克sigma项的贡献相当。 显示英文摘要

摘要： The nucleon matrix elements (NMEs) associated with quark chromo-magnetic dipole moments (cMDMs) play a crucial role in determining the CP-odd pion-nucleon couplings induced by quark chromo-electric dipole moments. In recent years, it has been argued that the NMEs of cMDMs can be related to the third moment of the nucleon's higher-twist (specifically, twist-three) parton distribution function (PDF) $e(x)$, which can, in principle, be measured through dihadron production in semi-inclusive deep inelastic scattering processes. By applying the spin-flavor expansion to the cMDM operators in the large-$N_c$ limit, where $N_c$ is the number of quark colors, we show that the NMEs receive contributions not only from the twist-three PDF $e(x)$ but also from an additional, previously neglected nucleon form factor. Incorporating constraints from the spin-flavor expansion, recent experimental data on $e(x)$, as well as model calculations of $e(x)$, we estimate the NMEs of the cMDM operators. Our analysis indicates that the NMEs are dominated by the nucleon form factors, and the cMDM contributions to pion-nucleon couplings can be comparable to those from the quark sigma terms.