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arXiv 0808.1973hep-th
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杨-米尔斯和QCD的MHV拉格朗日函数

MHV Lagrangians for Yang--Mills and QCD

James H. Ettle

摘要:

在过去的几十年里,人们已经意识到规范理论散射振幅的结构比传统的费曼图驱动方法所建议的要简单得多。特别是,帕克和泰勒发现了一个特别简单的表达式,表示两个不同螺旋度胶子的树能级振幅(所谓的MHV振幅)。Cachazo,Svrcek和Witten(CSW)设计了通过将低价MHV振幅与标量传播子缝合在一起来构建树级振幅的规则。曼斯菲尔德在2005年指出,可以构造场变量的正则变化,导致拉格朗日量的顶点与MHV振幅成比例,通过CSW的处方继续离壳,即所谓的正则MHV拉格朗日量。我们推导出这种变换的显式形式,并用它来表明,顶点确实是帕克-泰勒振幅高达5胶子。注意到CSW的MHV规则不能用于构建树级(-++)或单循环(+)振幅,我们扩展我们的工作,以增加MHV规则与所谓的完成顶点。这些允许通过规避S-矩阵等价定理来构造这些缺失的振幅。事实上,他们一起重建离壳光锥杨-米尔斯振幅代数。我们还给出了一个处方的规范MHV拉格朗日维正则化。最后,我们构造了一个典型的MHV拉格朗日与无质量费米子的基本表示使用类似的方法。

英文摘要:

Over the past few decades, it has been realised that gauge theory scattering amplitudes have structures much simpler than the traditional Feynman graph driven approach would suggest. In particular, Parke and Taylor found a particularly simple expression for the tree-level amplitudes with two gluons of different helicity than the others (the so-called MHV amplitudes). Cachazo, Svrcek and Witten (CSW) devised rules for constructing tree-level amplitudes by sewing lower-valence MHV amplitudes together with scalar propagators. It was shown by Mansfield in 2005 that a canonical change of the field variables could be constructed that resulted in a lagrangian whose vertices were proportional to MHV amplitudes, continued off-shell by CSW's prescription, the so-called Canonical MHV Lagrangian. We derive the explicit form of this transformation and use this to show that the vertices are indeed the Parke--Taylor amplitudes for up to five gluons. Noting that CSW's MHV rules cannot be used to construct the tree-level (-++) or one-loop (++++) amplitudes, we extend our work to augment the MHV rules with so-called completion vertices. These permit construction of these missing amplitudes by means of evasion of the S-matrix equivalence theorem. Indeed, together they reconstruct off-shell light-cone Yang-Mills amplitudes algebraically. We also give a prescription for dimensional regularisation of the Canonical MHV Lagrangian. Finally, we construct a canonical MHV lagrangian with massless fermions in the fundamental representation using a similar methodology.

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