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arXiv 1207.4458hep-th
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n维空间的引力振幅

Gravity Amplitudes from n-Space

Clifford Cheung

摘要:

我们确定了一个隐藏的GL(n,C)对称的树水平n点MHV重力振幅。这种对称性的表示存在于一个辅助的n空间中,其索引是外部粒子标签。旋量螺旋度变量在GL(n,C)下非线性变换,但在其显著子群、小群和置换群Sn下线性变换。利用GL(n,C)协变变量,我们提出了一个新的和简单的公式MHV振幅,可以推导出唯一的几何约束。这个表达式带有一个巨大的内在冗余,它可以通过n-空间中的一对参考3-平面来参数化。以一种特殊的方式固定这种冗余,我们再现了[1]的MHV振幅的S_{n-3}对称形式,作为矩阵树定理的结果,它又等价于[2]的S_{n-2}对称形式。振幅的冗余度也可以以完全保持S_n的方式固定,从而产生新的和明显S_n对称的MHV振幅形式。值得注意的是,这些表达式在旋量或质量维度上不需要明显同质。我们评论了N^{k-2}MHV振幅的可能扩展,并推测了GL(n,C)的更深起源。

英文摘要:

We identify a hidden GL(n,C) symmetry of the tree level n-point MHV gravity amplitude. Representations of this symmetry reside in an auxiliary n-space whose indices are external particle labels. Spinor helicity variables transform non-linearly under GL(n,C), but linearly under its notable subgroups, the little group and the permutation group S_n. Using GL(n,C) covariant variables, we present a new and simple formula for the MHV amplitude which can be derived solely from geometric constraints. This expression carries a huge intrinsic redundancy which can be parameterized by a pair of reference 3-planes in n-space. Fixing this redundancy in a particular way, we reproduce the S_{n-3} symmetric form of the MHV amplitude of [1], which is in turn equivalent to the S_{n-2} symmetric form of [2] as a consequence of the matrix tree theorem. The redundancy of the amplitude can also be fixed in a way that fully preserves S_n, yielding new and manifestly S_n symmetric forms of the MHV amplitude. Remarkably, these expressions need not be manifestly homogenous in spinorial weight or mass dimension. We comment on possible extensions to N^{k-2}MHV amplitudes and speculate on the deeper origins of GL(n,C).

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