相对论性重离子碰撞中的扩散还是反弹？

通过广义相对论反弹的宇宙学扰动

Cosmological Perturbations Through a General Relativistic Bounce

宇宙爆炸和循环的宇宙情景使人们重新认识到，今天宇宙中明显的密度扰动可能是在大爆炸之前的“前奇点”时代产生的。这些方案提供了明确的机制，使尺度不变的谱绝热扰动可能产生不需要宇宙暴胀，虽然在一个阶段之前的热大爆炸奇点。他们面临的一个关键问题是，是否存在一个独特的处方，通过反弹跟踪扰动，这个问题尚未得到最终解决。本文的目标是比较温和的，即研究既不违反广义相对论也不违反弱能量条件的弹跳宇宙模型。我们发现，一个扰动，这是纯粹的增长模式之前的反弹不匹配的纯衰减模式后的反弹扰动。给出了随动曲率扰动在反弹点附近变化的解析估计。它被发现，在一般情况下，它是必要的，以评估通过反弹的详细，而不是使用匹配条件的扰动的演变。

Curvature bounce in general relativity: background and primordial spectrum

Recent data suggest that the Universe could be positively curved. Combined with an inflationary stage, this might lead to a curvature bounce instead of the Big Bang. The background evolution is presented, as a function of the parameters controlling the cosmic evolution. The primordial tensor spectrum is also calculated and possible observational footprints of the model are underlined. Several potentials are considered and general remarks are made about "naturalness" in this context.

A pure general relativistic non-singular bouncing origin for the Universe

In this letter, we argue that the past of the Universe, extrapolated from standard physics and measured cosmological parameters, might be a non-singular bounce. We also show that, in this framework, quite stringent constraints can be put on the reheating temperature and number of inflationary e-folds, basically fixing $T_{RH}\sim T_{GUT}$ and $N\sim 70$. We draw some conclusions about the shape of the inflaton potential and raise the "naturalness" issue in this context. Finally, we argue that this could open a very specific window on the "pre big bounce" universe.

非奇异大反弹与线性涨落的演化

Non-singular big-bounces and evolution of linear fluctuations

我们认为，作为背景的弗里德曼世界模型的线性波动的演变，从收缩到膨胀阶段，通过光滑和非奇异的反弹阶段。在微扰方程中，只要重力超过压力梯度，膨胀阶段的增长模式就具有振幅守恒的特征，我们称之为C模式。在具有无压介质的球形几何中，我们证明了存在一个特殊的规范不变组合Φ，它在从大爆炸到大挤压的整个演化过程中保持不变，即使在反弹之后也具有相同的值：它表征了C模的系数。我们使用反弹模型的压力梯度项是可以忽略不计的反弹过程中，这需要额外存在的一个外来物质的结果。在这样的反弹中，即使在反弹之前和之后的状态方程的更一般的情况下，扩张阶段中的C-模式也只受收缩阶段中的C-模式的影响，因此，随着世界模型进入扩张阶段，收缩阶段中的增长模式衰减。在背景曲率在反弹期间具有显著作用的情况下，压力梯度项变得重要，并且我们不能将膨胀阶段中的C模式追踪到反弹之前的C模式。在这种情况下，流体反弹模型中的扰动表现出指数不稳定性，而标量场反弹模型中的扰动则表现出振荡行为。

Universal features of quantum bounce in loop quantum cosmology

In this Letter, we study analytically the evolutions of the flat Friedmann-Lemaitre-Robertson-Walker (FLRW) universe and its linear perturbations in the framework of {\em the dressed metric approach} in loop quantum cosmology (LQC). Assuming that the evolution of the background is dominated by the kinetic energy of the inflaton at the quantum bounce, we find that both evolutions of the background and its perturbations are independent of the inflationary potentials during the pre-inflationary phase. During this period the effective potentials of the perturbations can be well approximated by a P…

模糊反弹

Fuzzy Bounces

本文提出基于比安基恒等式约束的模糊因子涂抹方法，研究两类宇宙学反弹解的稳定性与演化。