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arXiv 2002.00834gr-qcastro-ph.COhep-lathep-th
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正则量子引力对引力波方程的修正

Modifications to Gravitational Wave Equation from Canonical Quantum Gravity

Andrea Dapor, Klaus Liegener

摘要:

人们期望时空的量子性质在所有的半经典引力系统中留下印记,至少在某些区域,包括引力波。在本文中,我们调查这样的印记引力波在一个特定的框架内:空间被假定为离散的(在一个规则的立方晶格的形式),这种离散的几何量子化以下狄拉克的正则量子化方案。然后通过将半经典态上的哈密顿算符的期望值提升到有效哈密顿量来提取半经典行为。考虑一族半经典态对Minkowski背景的小张量扰动,导出了量子修正的有效波动方程。对经典引力波方程的偏离被编码在一个修正的色散关系中,并受晶格离散参数的控制。对于有限离散,出现了几个有趣的效果:我们调查这些修改后的引力子的物理性质,并在一定的假设下,推导出张量功率谱的宇宙微波背景。后者被发现偏离经典的预测,在放大的UV模式发生。我们讨论了在什么情况下,这种效果可以与观察一致。

英文摘要:

It is expected that the quantum nature of spacetime leaves its imprint in all semiclassical gravitational systems, at least in certain regimes, including gravitational waves. In this paper we investigate such imprints on gravitational waves within a specific framework: space is assumed to be discrete (in the form of a regular cubic lattice), and this discrete geometry is quantised following Dirac's canonical quantisation scheme. The semiclassical behavior is then extracted by promoting the expectation value of the Hamiltonian operator on a semiclassical state to an effective Hamiltonian. Considering a family of semiclassical states representing small tensor perturbations to Minkowski background, we derive a quantum-corrected effective wave equation. The deviations from the classical gravitational wave equation are found to be encoded in a modified dispersion relation and controlled by the discreteness parameter of the underlying lattice. For finite discretisations, several interesting effects appear: we investigate the thermodynamical properties of these modified gravitons and, under certain assumptions, derive the tensor power spectrum of the cosmic microwave background. The latter is found to deviate from the classical prediction, in that an amplification of UV modes takes place. We discuss under what circumstances such effect can be in agreement with observations.

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