过山车宇宙学
Rollercoaster Cosmology
摘要：
（摘要）通货膨胀是否必须一次性发生？答案是一个响亮的不！所有的宇宙学问题都可以通过一系列短暂的宇宙加速爆发来解决，这些爆发被短暂的减速膨胀所打断。如果最后一个${\cal O}(50)-{\cal O}(60)$ e倍的最早阶段至少是${\cal O}(15)$ e倍长，扰动谱仍将与CMB和LSS匹配。其他阶段可以短得多。但是只要它们加起来达到${\cal O}(50)-{\cal O}(60)$的倍数，并且它们之间的减速膨胀阶段更短，而且总体上持续时间更短，那么随之而来的宇宙学就会通过检验。中断的存在重置每个加速阶段的efold时钟，并在CMB枢轴点改变其值。这种变化打开了理论空间，放松了界限。特别是在${\cal N}=60$中似乎被排除的一些模型非常适合作为${\cal N}=30$的较短阶段。有趣的预测是，无论是标量和张量谱的扰动迅速修改在短波长。这些特征可以用未来的CMB光谱搜索和短波长原始重力探测器进行测试。这些模型中的空间曲率可以大于最大波长标量扰动，因为$Ω_{\tt k}$与标量扰动$\frac{δρ}ρ|_{\tt S}$不同地演化。最后，在许多短的加速膨胀阶段，来自先前加速阶段的再加热产物的丰度不会被完全消除。这意味着宇宙中可能含有比可见粒子更稀少的粒子群，甚至可能含有原始的黑洞，这些黑洞是在最后一次再加热之前的减速时期产生的，可能是暗物质。
英文摘要：
(Abridged) Does inflation have to happen all in one go? The answer is a resounding no! All cosmological problems can be solved by a sequence of short bursts of cosmic acceleration, interrupted by short epochs of decelerated expansion. The spectrum of perturbations will still match the CMB and LSS if the earliest stage of the last ${\cal O}(50)-{\cal O}(60)$ efolds is at least ${\cal O}(15)$ efolds long. Other stages can be considerably shorter. But as long as they add up to ${\cal O}(50)-{\cal O}(60)$ efolds and the stages of decelerated expansion in between them are shorter and also overall last less, the ensuing cosmology will pass muster. The presence of the interruptions resets the efold clock of each accelerating stage, and changes its value at the CMB pivot point. This change opens up the theory space, loosening the bounds. In particular some models that seem excluded at ${\cal N}=60$ fit very well as shorter stages with ${\cal N}=30$. Interesting predictions are that both the scalar and tensor spectra of perturbations are rapidly modified at short wavelengths. These features could be tested with future CMB spectroscopy searches and with short wavelength primordial gravity probes. The spatial curvature in these models can be larger than the largest wavelength scalar perturbations, because $Ω_{\tt k}$ evolves differently than the scalar perturbations $\frac{δρ}ρ|_{\tt S}$. Finally, with many short stages of accelerated expansion, the abundance of reheating products from previous accelerated stages does not get completely wiped out. This implies that the universe may contain additional populations of particles, more rare than the visible ones, or even primordial black holes, created during a late decelerated epoch before last reheating, which may be dark matter.
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