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arXiv 2007.13745hep-th
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AdS中的Landau图与共形关联函数的S-矩阵

Landau diagrams in AdS and S-matrices from conformal correlators

Shota Komatsu, Miguel F. Paulos, Balt C. van Rees, Xiang Zhao

摘要:

AdS中的量子场论在边界上产生共形关联函数,并且在AdS几乎平坦的极限中,人们应该能够从这样的关联函数中提取S-矩阵。我们讨论一个特别简单的位置空间过程来做到这一点。它的特点是从边界位置到(壳层上)动量的直接映射,从而将交比与Mandelivery不变量联系起来。这个配方在几个例子中取得了成功,包括动量守恒的δ函数,并且可以被证明是基于梅林空间和OPE数据的arXiv:1607.06109中的两个建议。有趣的是,这个过程并不总是有效的:费曼图的朗道奇点被证明是更大区域的一部分,被称为“坏区域”,在那里威滕图的平面空间极限发散。为了捕捉这些分歧,我们介绍的概念,Landau图AdS。在平坦空间中,这些描述了在复杂空间中长距离传播的壳粒子,在每个体顶点都保持动量守恒。作为一个应用,我们恢复了四点三角图在坏区域边界处的异常阈值。

英文摘要:

Quantum field theories in AdS generate conformal correlation functions on the boundary, and in the limit where AdS is nearly flat one should be able to extract an S-matrix from such correlators. We discuss a particularly simple position-space procedure to do so. It features a direct map from boundary positions to (on-shell) momenta and thereby relates cross ratios to Mandelstam invariants. This recipe succeeds in several examples, includes the momentum-conserving delta functions, and can be shown to imply the two proposals in arXiv:1607.06109 based on Mellin space and on the OPE data. Interestingly the procedure does not always work: the Landau singularities of a Feynman diagram are shown to be part of larger regions, to be called `bad regions', where the flat-space limit of the Witten diagram diverges. To capture these divergences we introduce the notion of Landau diagrams in AdS. As in flat space, these describe on-shell particles propagating over large distances in a complexified space, with a form of momentum conservation holding at each bulk vertex. As an application we recover the anomalous threshold of the four-point triangle diagram at the boundary of a bad region.

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