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arXiv 0812.0351hep-thgr-qc
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引力中的迹Anomaly与无质量标量自由度

The Trace Anomaly and Massless Scalar Degrees of Freedom in Gravity

Maurizio Giannotti, Emil Mottola

摘要:

在电磁或引力背景下量子场的迹反常意味着在涉及应力-能量张量的物理振幅中存在无质量标量极。首先考虑轴向异常,并使用QED作为例子,我们计算了具有两个电流顶点的费米子应力张量的完整的单圈三角形振幅,<T^{mn} J^a J^b>,并在零电子质量m -> 0的极限下,展示了与迹异常相关的该振幅中的标量极。为了强调异常的红外方面,我们使用色散方法,并表明这种振幅和无质量标量极点的存在完全由其紫外有限项,以及真空的庞加莱不变性,Ja和Jb互换下的玻色对称性,矢量流和应力张量守恒的要求决定。我们导出了对应于三角形振幅不连续性的适当正谱函数的求和规则,表明它与k^2的δ函数成正比,因此在零电子质量的共形极限中包含一个无质量标量中间态。通过引入两个满足无质量波动方程的标量辅助场,可以用局部形式表示三角形振幅迹线所对应的有效作用量。这些无质量的标量自由度耦合到经典源,有助于引力散射过程,并可以有长距离的引力效应。

英文摘要:

The trace anomaly of quantum fields in electromagnetic or gravitational backgrounds implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. Considering first the axial anomaly and using QED as an example, we compute the full one-loop triangle amplitude of the fermionic stress tensor with two current vertices, <T^{mn} J^a J^b>, and exhibit the scalar pole in this amplitude associated with the trace anomaly, in the limit of zero electron mass m -> 0. To emphasize the infrared aspect of the anomaly, we use a dispersive approach and show that this amplitude and the existence of the massless scalar pole is determined completely by its ultraviolet finite terms, together with the requirements of Poincare invariance of the vacuum, Bose symmetry under interchange of J^a and J^b, and vector current and stress tensor conservation. We derive a sum rule for the appropriate positive spectral function corresponding to the discontinuity of the triangle amplitude, showing that it becomes proportional to delta function of k^2, and therefore contains a massless scalar intermediate state in the conformal limit of zero electron mass. The effective action corresponding to the trace of the triangle amplitude can be expressed in local form by the introduction of two scalar auxiliary fields which satisfy massless wave equations. These massless scalar degrees of freedom couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects.

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