介子主导图像中的轴矢量核子形状因子：色散视角下三角奇点的作用
The axial-vector nucleon form factor in the meson dominance picture: the role triangle singularities from a dispersive view
- Universidad de Granada（格拉纳达大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文从色散视角研究介子主导图像中轴矢量核子形状因子，发现ρπ三角图是轴介子主导的主要偏差来源，预测的轴半径与lattice QCD结果一致但与MINERνA结果不一致，并给出半经验公式。
AI中文摘要：
本文利用色散关系分析核子轴形状因子，该色散关系分别包含低动量区域的手征微扰理论（ChPT）和高动量区域的微扰量子色动力学（pQCD），这意味着针对A→N N̄谱函数存在一组超收敛求和规则。在N N̄产生阈值以下的类时区域，我们纳入a₁和a₁'共振态，其有限宽度效应通过ρπ和σπ中间态建模；在N N̄阈值以上，我们用非整数幂次衰减的径向激发1⁺⁺共振态无穷级数建模，最终与pQCD匹配。在此框架下，我们发现ChPT和pQCD的贡献均极小，而主导的ρπ三角图是轴介子主导的主要偏差来源。本计算并非拟合，其参数包含先验不确定性估计。轴半径被预测为r_A²=(0.28-0.33) fm²=(0.47-0.57 fm)²，与近期格点量子色动力学（lattice QCD）结果一致，但与MINERνA的测定结果不一致。本文还提供了一个简单的半经验公式，用于描述主要物理效应。
英文摘要：
The nucleon axial form factor is analyzed in terms of a dispersion relation comprising chiral perturbation theory (ChPT) and perturbative QCD (pQCD) in the low- and high-momentum regimes respectively, which implies a set of superconvergence sum rules for the $A \to N \bar N$ spectral function. In the timelike region below the $N \bar N$ production threshold we include the $a_1$ and $a_1'$ resonances, with finite-width effects modeled through $ρπ$ and $σπ$ intermediate states. Above the $N \bar N$ threshold, we model an infinite tower of radially excited $1^{++}$ resonances with a non-integer power fall-off, eventually matching pQCD. In this setup, we find that both the ChPT and pQCD contributions are tiny. In turn, the dominant $ρπ$ triangle provides the leading deviations from axial meson dominance. Our calculation is not a fit; it contains parameters with a priori uncertainties estimates. The axial radius is predicted to be $r_A^2 =(0.28-0.33)~\textrm{fm}^2 = ( 0.47-0.57~\textrm{fm})^2$ in agreement with recent lattice QCD results but inconsistent with the MINER$ν$A determination. A simple semiempirical formula is provided accounting for the main physical effects.
