标题： 一般慢收缩中的源项涨落 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，以及一类称为快速滚动模型的缩小范围的模型类别。 我们提出了标量和张量扰动超视界冻结的一般条件，并证明任何快速滚动模型都满足这些条件，就像在暴胀情况下的那样。 我们关注的是“源驱动反弹”场景，其中扰动由一个与反弹标量场耦合的$U(1)$规范场提供。 标度谱略微红倾斜的要求极大地限制了标量场与规范场之间的允许耦合。 我们表明，可以实现一个可行的略微红倾斜的标度谱。 然而，在快速滚动近似下，通常情况下张量与标量比值$r\simeq 1/9$，这与当前观测结果不符。 我们通过一个明确的例子（我们称之为“中间收缩”）展示了这一普遍结果。 我们证明了对快速滚动的小幅修正，如果不会改变格林函数，则不会导致超过一个 e-fold 的数据一致性$r<0.06$。 因此，成功的“源驱动反弹”需要不同的源或者显著偏离快速滚动。 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.