论文标题
高阶重力理论的各向异性不稳定
Anisotropic instability in a higher order gravity theory
论文作者
论文摘要
我们研究了一个度量立方重力理论，考虑了线性不均匀扰动的奇数模式，该模式在空间均匀的Bianchi I型I型歧管上，接近各向同性DE Sitter Spacetime。我们表明，与一般相对论相比，该理论具有新的自由度，该理论具有新的自由度，其动能在精确的各向同性的极限下消失。从大规模分散关系中，我们表明，这种理论始终具有一种幽灵模式以及非常短的时间（与哈勃时间）经典的速度（或幽灵 - 塔吉尼克人）的不稳定。为了确认我们的分析分析，我们还通过数值求解运动方程，我们发现这种不稳定性是在比例因子的单个电子折叠之前开发的。这表明这种重力理论不能用于构建可行的宇宙学模型。
We study a metric cubic gravity theory considering odd-parity modes of linear inhomogeneous perturbations on a spatially homogeneous Bianchi type I manifold close to the isotropic de Sitter spacetime. We show that in the regime of small anisotropy, the theory possesses new degrees of freedom compared to General Relativity, whose kinetic energy vanishes in the limit of exact isotropy. From the mass dispersion relation we show that such theory always possesses at least one ghost mode as well as a very short-time-scale (compared to the Hubble time) classical tachyonic (or ghost-tachyonic) instability. In order to confirm our analytic analysis, we also solve the equations of motion numerically and we find that this instability is developed well before a single e-fold of the scale factor. This shows that this gravity theory, as it is, cannot be used to construct viable cosmological models.
