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arXiv 0908.2420hep-ph
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P-奇和CP-奇四夸克对中子EDM的贡献

P-odd and CP-odd Four-Quark Contributions to Neutron EDM

Haipeng An, Xiangdong Ji, Fanrong Xu

摘要:

在一类超标准模型理论中,CP-奇观测量,如中子电偶极矩,从味中性P-奇和CP-奇四夸克算符中获得了重要的贡献。然而,这些算子的强子矩阵元中存在着相当大的不确定性,强烈地影响着理论中CP破坏参数的实验约束。本文在手征微扰理论和核子模型的结合下研究了它们的强子矩阵元。我们首先将算符分类在手征表象中,并给出首阶QCD演化。然后,我们匹配的四夸克算符的手征强子理论中相应的,发现矩阵元素之间的对称关系。虽然这使得格点量子色动力学计算可行,但我们选择在简单的夸克模型中估计非微扰匹配系数。最后,我们比较了中子电偶极矩和P-奇和CP-奇介子-核子耦合的结果与以前的研究使用朴素因子分解和QCD求和规则。我们的研究将对这些观测量中的强子物理不确定性提供有价值的见解。

英文摘要:

In a class of beyond-standard-model theories, CP-odd observables, such as the neutron electric dipole moment, receive significant contributions from flavor-neutral P-odd and CP-odd four-quark operators. However, considerable uncertainties exist in the hadronic matrix elements of these operators strongly affecting the experimental constraints on CP-violating parameters in the theories. Here we study their hadronic matrix elements in combined chiral perturbation theory and nucleon models. We first classify the operators in chiral representations and present the leading-order QCD evolutions. We then match the four-quark operators to the corresponding ones in chiral hadronic theory, finding symmetry relations among the matrix elements. Although this makes lattice QCD calculations feasible, we choose to estimate the non-perturbative matching coefficients in simple quark models. We finally compare the results for the neutron electric dipole moment and P-odd and CP-odd pion-nucleon couplings with the previous studies using naive factorization and QCD sum rules. Our study shall provide valuable insights on the present hadronic physics uncertainties in these observables.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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