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arXiv 1602.04459gr-qc
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线性化爱因斯坦理论和大质量引力中的能量动量张量:唯一性问题

Energy-momentum tensors in linearized Einstein's theory and massive gravity: The question of uniqueness

Jiří Bičák, Josef Schmidt

摘要:

在不使用变分方法的情况下,分析了线性化广义相对论和线性质量引力中能量动量张量的唯一性问题。我们从张量形式的自然类比开始(例如,它是一阶导数中二次项的线性组合),并要求它作为场方程的结果而守恒。在一般规范中的线性引力情形下,我们发现了一个四参数的二阶守恒张量系统,它包含唯一的对称张量。这就是在完整的广义相对论中经常用到的线性化的朗道-利夫希茨赝张量。本文阐明了四参数系统与Butcher等人最近在调和规范中提出的“基于物理基础”的表达式之间的关系,并指出在真空中高频波的情况下,经过适当的平均后,结果是一致的。在大质量引力中,我们证明了如何得到与“广义线性对称Landau-Lifshitz”张量相一致的表达式。然而,存在另一个唯一给定的更简单的对称张量,它可以通过将合适的超势的散度添加到Fierz-Pauli作用量的正则能量-动量张量来获得。与由涉及场变量的二阶导数的Belinfante程序导出的对称张量相反,该表达式仅包含场及其一阶导数。它比广义的朗道-利夫希茨张量简单,但两者产生相同的总量,因为它们的差异是超势的发散。我们还讨论了规范条件在唯一性证明中的作用。在附录中,简要介绍了符号张量操作软件Cadabra的使用。

英文摘要:

The question of the uniqueness of energy-momentum tensors in the linearized general relativity and in the linear massive gravity is analyzed without using variational techniques. We start from a natural ansatz for the form of the tensor (for example, that it is a linear combination of the terms quadratic in the first derivatives), and require it to be conserved as a consequence of field equations. In the case of the linear gravity in a general gauge we find a four-parametric system of conserved second-rank tensors which contains a unique symmetric tensor. This turns out to be the linearized Landau-Lifshitz pseudotensor employed often in full general relativity. We elucidate the relation of the four-parametric system to the expression proposed recently by Butcher et al. "on physical grounds" in harmonic gauge, and we show that the results coincide in the case of high-frequency waves in vacuum after a suitable averaging. In the massive gravity we show how one can arrive at the expression which coincides with the "generalized linear symmetric Landau-Lifshitz" tensor. However, there exists another uniquely given simpler symmetric tensor which can be obtained by adding the divergence of a suitable superpotential to the canonical energy-momentum tensor following from the Fierz-Pauli action. In contrast to the symmetric tensor derived by the Belinfante procedure which involves the second derivatives of the field variables, this expression contains only the field and its first derivatives. It is simpler than the generalized Landau-Lifshitz tensor but both yield the same total quantities since they differ by the divergence of a superpotential. We also discuss the role of the gauge conditions in the proofs of the uniqueness. In the Appendix, the use of the symbolic tensor manipulation software Cadabra is briefly described.

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