Contribution of the QCD Θ -term to the nucleon electric dipole moment
Contribution of the QCD Θ -term to the nucleon electric dipole moment
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DOI：
10.1103/physrevd.103.114507
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发表时间：
2021-01
影响因子：
6
通讯作者：
T. Bhattacharya;V. Cirigliano;Rajan Gupta;E. Mereghetti;B. Yoon
中科院分区：
文献类型：
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作者：
T. Bhattacharya;V. Cirigliano;Rajan Gupta;E. Mereghetti;B. Yoon
我们使用七个 2+1+1 风味 HISQ 系综来计算 θ 项对中子和质子电偶极矩的贡献。我们还估计 2+1+1 理论的拓扑磁化率在 Mπ = 135 MeV 的连续极限中为 χQ = (66(9)(4) MeV) 4。核子三点函数的计算是使用威尔逊-三叶草价夸克完成的。 CP 形状因数 F3 是通过在小 θ 中展开来计算的。我们证明，晶格伪影引入了一个与 a 成比例的项，该项在手性极限中不会消失，并且我们将其包含在我们的手性连续谱拟合中。手性微扰理论分析表明，N(0)π(0) 态应提供主要的激发态贡献，我们研究了这种态的影响。详细分析了使用两种消除激发态污染的策略对中子和质子电偶极矩的贡献。使用拟合两点函数的激发态谱，我们发现 dn 很小，|dn | 。 0.01 θ e · fm，而对于质子，我们得到 |dp | ∼ 0.02 θ e·fm。另一方面，如果主要激发态贡献来自 Nπ 态，则 |dn |可以大至 0.05 θ e · fm 和 |dp | ∼ 0.07 θ e·fm。我们的总体结论是，目前的晶格 QCD 计算无法提供 θ 项对核子电偶极矩贡献的可靠估计，并且需要高十倍的统计数据才能更好地控制系统性并可能获得 3σ 结果。
We present a calculation of the contribution of the Θ-term to the neutron and proton electric dipole moments using seven 2+1+1-flavor HISQ ensembles. We also estimate the topological susceptibility for the 2+1+1 theory to be χQ = (66(9)(4) MeV) 4 in the continuum limit at Mπ = 135 MeV. The calculation of the nucleon three-point function is done using Wilson-clover valence quarks. The CP form factor F3 is calculated by expanding in small Θ. We show that lattice artifacts introduce a term proportional to a that does not vanish in the chiral limit, and we include this in our chiralcontinuum fits. A chiral perturbation theory analysis shows that the N(0)π(0) state should provide the leading excited state contribution, and we study the effect of such a state. Detailed analysis of the contributions to the neutron and proton electric dipole moment using two strategies for removing excited state contamination are presented. Using the excited state spectrum from fits to the two-point function, we find dn is small, |dn | . 0.01 Θ e · fm, whereas for the proton we get |dp | ∼ 0.02 Θ e · fm. On the other hand, if the dominant excited-state contribution is from the Nπ state, then |dn | could be as large as 0.05 Θ e · fm and |dp | ∼ 0.07 Θ e · fm. Our overall conclusion is that present lattice QCD calculations do not provide a reliable estimate of the contribution of the Θ-term to the nucleon electric dipole moments, and a factor of ten higher statistics data are needed to get better control over the systematics and possibly a 3σ result.