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arXiv 0910.3653hep-phhep-th
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三圈及以上的软奇点

On soft singularities at three loops and beyond

Lance J. Dixon, Einan Gardi, Lorenzo Magnea

摘要:

我们报告了在理解无质量规范理论散射振幅的软奇异性方面的进一步进展。最近,基于Sudakov分解导出了一组方程,将多腿散射振幅的软反常维数矩阵约束为任意环阶,并将其与尖点反常维数相关联。这些方程的最小解被证明是色偶极子的和。在这里,我们探讨潜在的贡献软异常尺寸超越总和偶极子公式。这样的贡献受到因式分解和不变性的约束下重新标度的部分子动量的共形不变的交比的函数。因此,他们必须关联至少四个硬部分子的颜色和运动自由度,对应于连接四条程函线的胶子网,这四条程函线首先出现在三个环上。我们分析潜在的贡献,结合所有可用的约束,包括玻色对称性,预期程度的超越性,并在两个硬部分子成为共线的极限奇异结构。我们发现,如果运动学的依赖性仅仅是通过产品的交叉比的矩阵,然后在三个循环有一个独特的功能,是符合所有可用的约束。如果也允许出现多边形,则至少有两个附加结构与可用约束一致。

英文摘要:

We report on further progress in understanding soft singularities of massless gauge theory scattering amplitudes. Recently, a set of equations was derived based on Sudakov factorization, constraining the soft anomalous dimension matrix of multi-leg scattering amplitudes to any loop order, and relating it to the cusp anomalous dimension. The minimal solution to these equations was shown to be a sum over color dipoles. Here we explore potential contributions to the soft anomalous dimension that go beyond the sum-over-dipoles formula. Such contributions are constrained by factorization and invariance under rescaling of parton momenta to be functions of conformally invariant cross ratios. Therefore, they must correlate the color and kinematic degrees of freedom of at least four hard partons, corresponding to gluon webs that connect four eikonal lines, which first appear at three loops. We analyze potential contributions, combining all available constraints, including Bose symmetry, the expected degree of transcendentality, and the singularity structure in the limit where two hard partons become collinear. We find that if the kinematic dependence is solely through products of logarithms of cross ratios, then at three loops there is a unique function that is consistent with all available constraints. If polylogarithms are allowed to appear as well, then at least two additional structures are consistent with the available constraints.

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