Theoretical implications of detecting gravitational waves
Theoretical implications of detecting gravitational waves
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DOI：
10.1088/1475-7516/2015/08/008
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发表时间：
2014-10
影响因子：
6.4
通讯作者：
G. Geshnizjani;W. Kinney
中科院分区：
文献类型：
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作者：
G. Geshnizjani;W. Kinney
这篇论文是一系列定理中的第三篇，这些定理阐述了宇宙学观测如何为宇宙加速的早期阶段提供证据。 [1,2] 中证明，观测到的标量扰动的功率谱迫使所有可能的替代膨胀理论取代广义相对论以外的理论。结果表明，一般来说，如果没有加速膨胀阶段，这些替代方案必须至少打破经典广义相对论的以下原则之一：零能量条件（NEC）、亚光速信号传播或亚普朗克能量密度。在本文中，我们证明了大尺度原始引力波的探测如何能够提供独立证据来支持加速膨胀阶段。该证明不依赖于张量模式的谱指数，而是依赖于弯曲时空中量子场论的有效性以及源自绝热真空涨落的张量模式。我们的方法，就像标量的情况一样，是通过反证来证明的：我们使用宇宙微扰理论研究非加速、亚普朗克宇宙中真空涨落产生的可检测张量信号的可能性，并得出宇宙学动力学的矛盾极限。这一矛盾意味着我们关于早期宇宙的一个或多个公理必定已被打破。张量扰动的界限不仅独立于从标量功率谱获得的界限，而且比从标量功率谱获得的界限更强。
This paper is the third in a series of theorems which state how cosmological observations can provide evidence for an early phase of acceleration in the universe. It was demonstrated in [1,2], that the observed power spectrum for scalar perturbations forces all possible alternative theories of inflation to theories other than General Relativity. It was shown that generically, without a phase of accelerated expansion, these alternatives have to break at least one of the following tenets of classical general relativity: the Null Energy Condition (NEC), subluminal signal propagation, or sub-Planckian energy densities. In this paper we prove how detection of primordial gravitational waves at large scales can provide independent evidence to support a phase of accelerated expansion. This proof does not rely on the spectral index for tensor modes but relies on validity of quantum field theory in curved space time and tensor modes being sourced from adiabatic vacuum fluctuations. Our approach, like in the case of scalars, is proof by contradiction: we investigate the possibility of a detectable tensor signal sourced by vacuum fluctuations in a non-accelerating, sub-Planckian universe using cosmological perturbation theory and derive contradictory limits on cosmological dynamics. The contradiction implies that one or more of our axioms for early universe must have been broken. The bound from tensor perturbations is not only independent of, but also stronger than the one obtained from scalar power spectrum.