标题： 源波动在一般慢收缩中 显示英文标题

标题： Sourced fluctuations in generic slow contraction

摘要： 我们引入了一组适用于慢收缩宇宙的通用条件，以及一个被缩小的模型类别，称为快速滚动模型。 我们提出了标量和张量扰动在超视界尺度上冻结的普遍条件，并表明任何快速滚动模型都满足这些条件，就像膨胀的情况一样。 我们感兴趣的是“源 bounce”情景，在这种情景中，扰动由一个与 bounce 标量场耦合的$U(1)$规范场产生。 标量谱略微红移的要求极大地限制了标量场和规范场之间的允许耦合。 我们表明，可行的略微红移的标量谱是可以实现的。 然而，在快速滚动近似下，张量-标量比通常是$r\simeq 1/9$，与当前观测不一致。 我们通过一个显式的例子来证明这一普遍结果，我们称之为“中间收缩”。 我们证明了在快速滚动中进行的小修改，只要不改变格林函数，就不会在超过一个 e-折叠的情况下产生与数据一致的$r<0.06$。 因此，成功的“源 bounce”需要不同的来源或对快速滚动的显著偏离。 显示英文摘要

摘要： We introduce a set of generic conditions for the slow contracting Universe and for a narrowed-down category of models called fast-roll models. We present general conditions for super horizon freeze-out of scalar and tensor perturbations and show that any fast-roll model satisfies them, as in the case of inflation. We are interested in the "Sourced Bounce" scenario, where perturbations are sourced by a $U(1)$ gauge field coupled to a bouncer scalar field. The requirement of a slightly red tilted scalar spectrum greatly restricts the allowed couplings between the scalar and the gauge field. We show that a viable slightly red scalar spectrum is achievable. However, within the fast-roll approximation, the tensor-to-scalar ratio is in general $r\simeq 1/9$, inconsistent with current observations. We demonstrate the general result with an explicit example we dub "Intermediate contraction". We prove that small modifications in fast-roll that do not alter the Green's functions do not result in $r<0.06$ consistent with the data for more than an e-fold. Hence, a successful "Sourced Bounce" requires a different source or a significant deviation from fast-roll.