标题： 光子到介子转换形式因子和介子分布幅度从全息QCD 显示英文标题

标题： Photon-to-pion transition form factor and pion distribution amplitude from holographic QCD

摘要： 我们试图在全息QCD方法中理解最近观察到的光子到π介子转换形式因子的异常行为。 首先回顾并应用了异常\gamma ^*\gamma ^*\pi ^0 形式因子的全息描述到各种模型中。 说明在描述异常形式因子时，全息方法在渐近意义上与微扰QCD（pQCD）框架对偶，其中π介子模\pi (z)\sim z 对应于渐近π介子分布振幅。 这表明在光锥全息理论中存在一些不一致之处，因为 \pi (z)\sim z 在那里应与 \varphi (x)\sim \sqrt{x(1-x)} 对应。 在澄清这些细微差别之后，我们利用全息表达式和微扰表达式之间的关系来研究过渡形式因子可能的渐近违反情况。 结果发现，如果要求渐近形式因子具有类似pQCD的表达式，则介子模式只能通过对数因子在紫外区域增强。 则最小变形的介子模式将具有形式\pi (z)\sim z\ln (z\Lambda )^{-1}。我们假设这种变形可能是由于介子与非平凡的开放弦快子场耦合，然后参数$\Lambda$将与夸克凝聚有关。有趣的是，这个介子模式直接导致Radyushkin的对数模型，该模型在大-Q^2区域与实验数据拟合得很好。另一方面，由Radyushkin和Polyakov提出的具有类似平坦的介子分布振幅的pQCD解释，无法具有全息表达式。 显示英文摘要

摘要： We try to understand the recently observed anomalous behavior of the photon-to-pion transition form factor in the holographic QCD approach. First the holographic description of the anomalous \gamma^*\gamma^*\pi^0 form factor is reviewed and applied to various models. It is illustrated that in describing the anomalous form factor, the holographic approach is asymptotically dual to the perturbative QCD (pQCD) framework, with the pion mode \pi(z)\sim z corresponding to the asymptotic pion distribution amplitude. This indicates some inconsistency in light-front holography, since \pi(z)\sim z would be dual to \varphi(x)\sim \sqrt{x(1-x)} there. After clarifying these subtleties, we employ the relation between the holographic and the perturbative expressions to study possible asymptotic violation of the transition form factor. It is found that if one require that the asymptotic form factor possess a pQCD-like expression, the pion mode can only be ultraviolet-enhanced by logarithmic factors. The minimally deformed pion mode will then be of the form \pi(z)\sim z\ln (z\Lambda)^{-1}. We suppose that this deformation may be due to the coupling of the pion with a nontrivial open string tachyon field, and then the parameter $\Lambda$ will be related to the quark condensate. Interestingly, this pion mode leads immediately to Radyushkin's logarithmic model, which fitted very well the experimental data in the large-Q^2 region. On the other side, the pQCD interpretation with a flat-like pion distribution amplitude, proposed by Radyushkin and Polyakov, fails to possess a holographic expression.