Stealth dark energy in scordatura DHOST theory
Stealth dark energy in scordatura DHOST theory
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DOI：
10.1088/1475-7516/2021/03/081
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发表时间：
2020-09
影响因子：
6.4
通讯作者：
M. Gorji;H. Motohashi;S. Mukohyama
中科院分区：
文献类型：
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作者：
M. Gorji;H. Motohashi;S. Mukohyama
纯量-张量理论中的隐形德西特解具有精确的德西特背景度规和非平凡的纯量场轮廓。最近，在简并高阶标量张量（DHOST）理论的背景下，它表明隐形de Sitter解决方案遭受无限强耦合或梯度不稳定的标量场扰动。声速的平方要么为零，要么为负。在第一种情况下，强耦合尺度为零，因此低于任何物理现象的能量尺度。从有效场论的观点来看，这个问题自然可以通过引入一个被称为scordatura的简并条件的受控失谐来解决，恢复了一个版本的鬼凝聚。本文基于一个隐形宇宙学解，在Scordatura DHOST理论中构造了一个可行的暗能量模型，该模型的度规与标准ΛCDM模型中的相同，标量场的轮廓与时间线性相关.我们发现，scordatura机制解决了强耦合和梯度不稳定性。此外，我们发现，scordatura也是必要的，使准静态极限定义良好，这意味着在视界下的观测量不可避免地受到scordatura的影响。我们导出了有效的引力耦合和对线性暗物质能量密度衬度以及Weyl势和引力滑移参数的视界下演化的摩擦项的修正。在没有scordatura的情况下，即使无限强耦合的问题被不公正地忽略，准静态近似在隐形宇宙学解周围的所有尺度上都会崩溃。因此，在考虑scordatura效应的情况下，需要重新审视文献中关于修正重力下物质密度对比的视界下演化的估计。
A stealth de Sitter solution in scalar-tensor theories has an exact de Sitter background metric and a nontrivial scalar field profile. Recently, in the context of Degenerate Higher-Order Scalar-Tensor (DHOST) theories it was shown that stealth de Sitter solutions suffer from either infinite strong coupling or gradient instability for scalar field perturbations. The sound speed squared is either vanishing or negative. In the first case, the strong coupling scale is zero and thus lower than the energy scale of any physical phenomena. From the viewpoint of effective field theory, this issue is naturally resolved by introducing a controlled detuning of the degeneracy condition dubbed scordatura, recovering a version of ghost condensation. In this paper we construct a viable dark energy model in the scordatura DHOST theory based on a stealth cosmological solution, in which the metric is the same as in the standard ΛCDM model and the scalar field profile is linearly time-dependent. We show that the scordatura mechanism resolves the strong coupling and gradient instability. Further, we find that the scordatura is also necessary to make the quasi-static limit well-defined, which implies that the subhorizon observables are inevitably affected by the scordatura. We derive the effective gravitational coupling and the correction to the friction term for the subhorizon evolution of the linear dark matter energy density contrast as well as the Weyl potential and the gravitational slip parameter. In the absence of the scordatura, the quasi-static approximation would break down at all scales around stealth cosmological solutions even if the issue of the infinite strong coupling is unjustly disregarded. Therefore previous estimations of the subhorizon evolution of matter density contrast in modified gravity in the literature need to be revisited by taking into account the scordatura effect.