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arXiv 0903.1126hep-phhep-th
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规范理论振幅的红外奇异性结构

On the Structure of Infrared Singularities of Gauge-Theory Amplitudes

Thomas Becher, Matthias Neubert

摘要:

本文给出了具有任意数目支腿和环的维数正则化无质量规范理论散射振幅的红外奇异性的封闭公式。它来自于软共线有效理论中n-jet算子维数矩阵的全阶猜想。我们发现,这种反常的尺寸的形式是严格限制软共线分解,非阿贝尔指数,共线极限的振幅的行为。使用图解分析,我们表明,这些限制意味着,三圈秩序的异常尺寸只涉及两个部分子的相关性,与可能的例外的一个单一的颜色结构乘以一个函数的共形交比取决于动量的四个外部部分子,这将不得不消失在所有的两个粒子共线的限制。我们认为,这样的功能不会出现在三个循环的顺序,并在更高的订单也是如此。我们的公式预测卡西米尔缩放的尖点异常尺寸的所有订单微扰理论,我们明确检查的约束排除在四个循环的外观更高的卡西米尔不变量。利用夸克和胶子形状因子的已知结果,我们导出了1/n ^n极项(n=1,.,6)对于无质量QCD中任意n部分子散射振幅。这推广了Catani在1998年提出的双环公式。

英文摘要:

A closed formula is obtained for the infrared singularities of dimensionally regularized, massless gauge-theory scattering amplitudes with an arbitrary number of legs and loops. It follows from an all-order conjecture for the anomalous-dimension matrix of n-jet operators in soft-collinear effective theory. We show that the form of this anomalous dimension is severely constrained by soft-collinear factorization, non-abelian exponentiation, and the behavior of amplitudes in collinear limits. Using a diagrammatic analysis, we demonstrate that these constraints imply that to three-loop order the anomalous dimension involves only two-parton correlations, with the possible exception of a single color structure multiplying a function of conformal cross ratios depending on the momenta of four external partons, which would have to vanish in all two-particle collinear limits. We argue that such a function does not appear at three-loop order, and that the same is true in higher orders. Our formula predicts Casimir scaling of the cusp anomalous dimension to all orders in perturbation theory, and we explicitly check that the constraints exclude the appearance of higher Casimir invariants at four loops. Using known results for the quark and gluon form factors, we derive the three-loop coefficients of the 1/epsilon^n pole terms (with n=1,...,6) for an arbitrary n-parton scattering amplitude in massless QCD. This generalizes Catani's two-loop formula proposed in 1998.

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