近日，西班牙巴塞罗那自治大学的Francesco Sciotti课题组与瑞士日内瓦大学的Francesco Riva合作，并取得一项新进展。经过不懈努力，他们揭示了大Nc量子色动力学（QCD）转向中具有正定边界的现象。相关研究成果已于2023年6月16日在国际知名学术期刊《高能物理杂志》上发表。
在前期研究的基础上，该研究团队通过探索手征拉格朗日参数和介子与π介子的耦合的允许区域，揭示了具有正定边界的大Nc量子色动力学（QCD）转向的现象。研究人员发现，在手征展开的各阶中存在着扭曲结构，并开发了分析工具来证明这些扭曲与具有单个轻子极点的振幅相对应。此外，他们构建了（无标量和无矢量）Lovelace-Shapiro和Coon紫外完备振幅的变形，并发现它们位于边界附近。
研究人员指出，交叉对称性的限制意味着随着自旋增加，介子与π介子的耦合将变得更小，这解释了矢量介子主导和全息量子色动力学的成功。此外，他们还研究了这些结论在振幅高能行为假设方面的依赖性。最后，他们强调了该研究结果与格点计算在探索大Nc量子色动力学中的互补性。
据悉，大Nc极限下介子散射振幅的简单解析结构以及光谱密度的正定性为低能观测提供了准确的预测。
附：英文原文
Title: Cornering large-Nc QCD with positivity bounds
Author: Fernandez, Clara, Pomarol, Alex, Riva, Francesco, Sciotti, Francesco
Issue&Volume: 2023-06-16
Abstract: The simple analytic structure of meson scattering amplitudes in the large-Nc limit, combined with positivity of the spectral density, provides precise predictions on low-energy observables. Building upon previous studies, we explore the allowed regions of chiral Lagrangian parameters and meson couplings to pions. We reveal a structure of kinks at all orders in the chiral expansion and develop analytical tools to show that kinks always correspond to amplitudes with a single light pole. We build (scalar- and vector-less) deformations of the Lovelace-Shapiro and Coon UV-complete amplitudes, and show that they lie close to the boundaries. Moreover, constraints from crossing-symmetry imply that meson couplings to pions become smaller as their spin increases, providing an explanation for the success of Vector Meson Dominance and holographic QCD. We study how these conclusions depend on assumptions about the high-energy behavior of amplitudes. Finally, we emphasize the complementarity between our results and Lattice computations in the exploration of large-Nc QCD.
DOI: 10.1007/JHEP06(2023)094
Source: https://link.springer.com/article/10.1007/JHEP06(2023)094