论文标题
在收缩宇宙学中的量子波动不可避免的剪切
Unavoidable shear from quantum fluctuations in contracting cosmologies
论文作者
论文摘要
众所周知，合同的宇宙学存在剪切不稳定性，其中各向异性应力对整体能量密度的贡献增长为$ a^{ - 6} $，而$ a $ a $ a $ a the比例因子。从经典上讲，在反弹之前，这种贡献是否变得重要，取决于其初始值，这总是可以进行充分调整以使其无关紧要。但是，真空量子波动不可避免地提供了各向异性应力的非逐渐变化来源。在这项工作中，我们计算如果假设最初消失的最小剪切量，则可以使量子波动构建。实际上，我们考虑了一个无质量的测试标量场，并通过随机的“通货膨胀”（尽管在此应用于合同阶段）形式主义来描述其量子波动。我们发现，如果收缩的状态方程参数满足$ W> -1/9 $，无论何时启动合同阶段，剪切变量始终是当哈勃尺度接近planck质量的时候（这也是预期反弹的地方）。但是，如果$ w <-1/9 $，则剪切反应变得更加重要，这取决于整体收缩量。
Contracting cosmologies are known to be flawed with a shear instability, where the contribution from the anisotropic stress to the overall energy density grows as $a^{-6}$, with $a$ the scale factor. Classically, whether or not this contribution becomes important before the bounce depends on its initial value, which can always be sufficiently fine tuned to make it irrelevant. However, vacuum quantum fluctuations inevitably provide a non-vanishing source of anisotropic stress. In this work, we compute the minimum amount of shear that is obtained if one assumes that it vanishes initially, but lets quantum fluctuations build it up. In practice, we consider a massless test scalar field, and describe its quantum fluctuations by means of the stochastic "inflation" (though here applied to a contracting phase) formalism. We find that, if the equation-of-state parameter of the contraction satisfies $w>-1/9$, regardless of when the contracting phase is initiated, the time at which the shear becomes sizeable is always when the Hubble scale approaches the Planck mass (which is also where the bounce is expected to take place). However, if $w<-1/9$, the shear backreaction becomes important much earlier, at a point that depends on the overall amount of contraction.
