论文标题
标准模型中夸克铬磁偶极矩的新估计值
New estimate of the chromomagnetic dipole moment of quarks in the standard model
论文作者
论文摘要
列出了标准模型对铬磁偶极矩（CMDM）$ \hatμ_Q（q^2）$ Quarks $ \ hat hatμ_Q（q^2）$的一个新估计值，目的是解决先前计算中引起的一些分歧。我们考虑了带有转移动量$ q^2 $的最通用的情况，并根据Feynman参数积分和Passarino-Veltman标量函数获得分析结果，然后在可能的情况下以封闭形式的功能表示。该计算是通过可重算法的线性$r_ξ$ gauge和背景字段方法完成的，该方法使人们能够证实所产生的$ \ hatμ_Q（q^2）$是独立的，因此是有效的可观察数量。发现来自三灰色Feynman图的QCD贡献具有红外差异，这与先前的评估一致，并且源于静态CMDM [$ \hatμ（0）$]对扰动QCD没有任何意义。对于数值分析，我们考虑区域30 GEV $ <\ | <| <| <$ 1000 GEV，并分析所有标准模型夸克的$ \ hatμ_q（q^2）$的行为。发现光夸克的CMDM比顶部夸克的CMDM小得多，因为它与夸克质量成正比。在经过考虑的能量间隔中，$ \hatμ_t（q^2）$的真实和虚构部分均为$ 10^{ - 2} -2} -10^{ - 3} $，其中最大的贡献是QCD引起的图表产生的，尽管在threshold $ q^2 = 4m_t^2 $ g的范围内也有重要的贡献。 交换。
A new estimate of the one loop contributions of the standard model to the chromomagnetic dipole moment (CMDM) $\hat μ_q(q^2)$ of quarks is presented with the aim to address a few disagreements arising in previous calculations. We consider the most general case with an off-shell gluon with transfer momentum $q^2$ and obtain analytical results in terms of Feynman parameter integrals and Passarino-Veltman scalar functions, which are then expressed in terms of closed form functions when possible. The calculation is done via a renormalizable linear $R_ξ$ gauge and the background field method, which allows one to corroborate that the resulting $\hat μ_q(q^2)$ is gauge independent and thus a valid observable quantity. It is found that the QCD contribution from a three-gluon Feynman diagram has an infrared divergence, which agrees with a previous evaluation and stems from the fact that the static CMDM [$\hatμ(0)$] has no sense in perturbative QCD. For the numerical analysis we consider the region 30 GeV$<\|q\|<$ 1000 GeV and analyze the behavior of $\hat μ_q(q^2)$ for all the standard model quarks. It is found that the CMDM of light quarks is considerably smaller than that of the top quark as it is directly proportional to the quark mass. In the considered energy interval, both the real and imaginary parts of $\hatμ_t(q^2)$ are of the order of $10^{-2}-10^{-3}$, with the largest contribution arising from the QCD induced diagrams, though around the threshold $q^2=4m_t^2$ there are also important contributions from diagrams with $Z$ gauge boson and Higgs boson exchange.
