标题： 能否通过观测区分绝热Quartessence与LambdaCDM？ 显示英文标题

标题： Is it possible to observationally distinguish adiabatic Quartessence from LambdaCDM?

摘要： 在四元数模型中的状态方程（EOS）在两个阶段之间进行插值：高能量密度下的 $p\simeq 0$ 和低能量密度下的 $p\approx -\rho$。 在迄今为止分析的四元数模型中，EOS 是凸的，这意味着随着宇宙膨胀能量密度的降低，绝热声速（$c_{s}^{2}$）增加。 最近一段时间内非可忽略的 $c_{s}^{2}$ 是导致困扰所有凸（非静音）四元数模型的物质功率谱问题的根源。 这些宇宙学模型的可行性仅可能在几乎完美模仿 $\Lambda$冷暗物质（CDM）的极限情况下成立。 在这项工作中，我们研究了在宇宙演化过程中 EOS 凹凸性发生变化的一类四元数模型是否也需要与 $\Lambda$冷暗物质（CDM）相似。 我们将分析集中在这样一个简单情况中，即 EOS 具有阶跃形状，在非常早期的时间 $p\simeq0$，而在晚期时间 $p\simeq const<0$。 对于这类模型，一个不可忽略的 $c_{s}^{2}$是一种瞬态现象，并且可能仅在更早的时期内相关。 我们表明，与大量宇宙学数据一致需要这两个渐近状态之间的转变发生在高红移（$z_t\gtrsim38$）。 这使我们推测任何成功的非静默四分量的宇宙膨胀历史（实际上）与 $\Lambda$CDM 的历史相同。 显示英文摘要

摘要： The equation of state (EOS) in quartessence models interpolates between two stages: $p\simeq 0$ at high energy densities and $p\approx -\rho$ at small ones. In the quartessence models analyzed up to now, the EOS is convex, implying increasing adiabatic sound speed ($c_{s}^{2}$) as the energy density decreases in an expanding Universe. A non-negligible $c_{s}^{2}$ at recent times is the source of the matter power spectrum problem that plagued all convex (non-silent) quartessence models. Viability for these cosmologies is only possible in the limit of almost perfect mimicry to $\Lambda$CDM. In this work we investigate if similarity to $\Lambda$CDM is also required in the class of quartessence models whose EOS changes concavity as the Universe evolves. We focus our analysis in the simple case in which the EOS has a step-like shape, such that at very early times $p\simeq0$, and at late times $p\simeq const<0$. For this class of models a non-negligible $c_{s}^{2}$ is a transient phenomenon, and could be relevant only at a more early epoch. We show that agreement with a large set of cosmological data requires that the transition between these two asymptotic states would have occurred at high redshift ($z_t\gtrsim38$). This leads us to conjecture that the cosmic expansion history of any successful non-silent quartessence is (practically) identical to the $\Lambda$CDM one.