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arXiv 2004.13057hep-thgr-qchep-ph
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共形场论中能量动量张量的解析约束

Analytic constraints on the energy-momentum tensor in conformal field theories

Cédric Lorcé, Peter Lowdon

摘要:

在这项工作中,我们研究了四维幺正、局域和庞加莱协变量子场论中无质量壳层态的能量动量张量的矩阵元。我们证明,这些矩阵元素可以参数化的洛伦兹发电机的协变多极,这引起了一个形状因子分解,其中螺旋度的依赖状态的因式分解。利用这种分解,我们继续探索共形场论的某些结果,推导出由共形对称性所施加的明确的分析条件,并用例子来说明它们唯一地固定了矩阵元素的形式。我们还提供了新的见解所施加的限制,无质量粒子的存在,特别是无质量的自由理论必然是共形的。

英文摘要:

In this work we investigate the matrix elements of the energy-momentum tensor for massless on-shell states in four-dimensional unitary, local, and Poincaré covariant quantum field theories. We demonstrate that these matrix elements can be parametrised in terms of covariant multipoles of the Lorentz generators, and that this gives rise to a form factor decomposition in which the helicity dependence of the states is factorised. Using this decomposition we go on to explore some of the consequences for conformal field theories, deriving the explicit analytic conditions imposed by conformal symmetry, and using examples to illustrate that they uniquely fix the form of the matrix elements. We also provide new insights into the constraints imposed by the existence of massless particles, showing in particular that massless free theories are necessarily conformal.

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