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arXiv 2103.02054hep-ph
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核子轴矢量和赝标形状因子及PCAC关系

Nucleon axial-vector and pseudoscalar form factors, and PCAC relations

Chen Chen, Christian S. Fischer, Craig D. Roberts, Jorge Segovia

摘要:

我们用连续夸克+双夸克方法研究相对论量子场论中的核子束缚态问题,给出了核子轴向和诱导赝标形状因子$G_A$和$G_P$的无参数预言,并将它们统一为赝标形状因子$G_5$或π-核子形状因子$G_{πNN}$ .我们解释了如何部分守恒的轴向矢量电流和相关的Goldberger-Treiman关系得到满足,一旦所有必要的耦合的外部电流的构建块的核子是一致的,特别是,我们完全解决了海鸥耦合的双夸克顶点与轴向矢量和赝标电流。在我们描述的结果中,以下是值得强调的。由轴向电荷$g_A=G_A(0)=1.25(3)$和质量尺度$M_A = 1.23(3) m_N$定义的偶极形状因子($m_N$是核子质量)可以精确地描述$G_A$的逐点行为。关于$G_P$,我们得到了赝标电荷$g_p^\ast = 8.80(23)$,并发现π极点优势的方法提供了一个可靠的估计的直接计算结果。我们计算的π-核子耦合常数$g_{πNN}/m_N =14.02(33)/{\rm GeV}$与最近的精确测定值是一致的。

英文摘要:

We use a continuum quark+diquark approach to the nucleon bound-state problem in relativistic quantum field theory to deliver parameter-free predictions for the nucleon axial and induced pseudoscalar form factors, $G_A$ and $G_P$, and unify them with the pseudoscalar form factor $G_5$ or, equivalently, the pion-nucleon form factor $G_{πNN}$. We explain how partial conservation of the axial-vector current and the associated Goldberger-Treiman relation are satisfied once all necessary couplings of the external current to the building blocks of the nucleon are constructed consistently; in particular, we fully resolve the seagull couplings to the diquark-quark vertices associated with the axial-vector and pseudoscalar currents. Among the results we describe, the following are worth highlighting. A dipole form factor defined by an axial charge $g_A=G_A(0)=1.25(3)$ and a mass-scale $M_A = 1.23(3) m_N$, where $m_N$ is the nucleon mass, can accurately describe the pointwise behaviour of $G_A$. Concerning $G_P$, we obtain the pseudoscalar charge $g_p^\ast = 8.80(23)$, and find that the pion pole dominance approach delivers a reliable estimate of the directly computed result. Our computed value of the pion-nucleon coupling constant, $g_{πNN}/m_N =14.02(33)/{\rm GeV}$ is consistent with recent precision determinations.

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