标题： 早期暗能量的冻结现象 显示英文标题

标题： Freezing Out Early Dark Energy

摘要： 探索了一种暗能量的唯象学模型，在早期时追踪重子和冷暗物质，而在晚期则类似于宇宙常数。在这两种状态之间的转变过程中，暗能量密度迅速下降，就像一种冷冻出来的遗迹粒子，此时状态方程达到+1峰值。暗能量密度从标度到势能主导的这种调整可能是触发机制的标志，有助于解释晚期宇宙加速膨胀。我们表明，早期非可忽略的暗能量密度以及在转变时状态方程的峰值，在宇宙微波背景各向异性模式和大尺度结构增长速率上留下了印记。该模型引入了两个新参数，分别是当今的状态方程和冻结转变的红移。对十维参数空间进行了蒙特卡洛马尔科夫链分析，以比较该模型与Planck之前的宇宙微波背景、大尺度结构和超新星数据及哈勃常数测量值。我们发现，由该模型描述的转变可能发生在红移z~400这么晚的时间点。我们探讨了未来宇宙微波背景和弱透镜实验对该模型施加更严格限制的能力。该模型的可行性可能暗示了暗能量模型构建中解决巧合问题的新方向。 显示英文摘要

摘要： A phenomenological model of dark energy that tracks the baryonic and cold dark matter at early times but resembles a cosmological constant at late times is explored. In the transition between these two regimes, the dark energy density drops rapidly as if it were a relic species that freezes out, during which time the equation of state peaks at +1. Such an adjustment in the dark energy density, as it shifts from scaling to potential-domination, could be the signature of a trigger mechanism that helps explain the late-time cosmic acceleration. We show that the non-negligible dark energy density at early times, and the subsequent peak in the equation of state at the transition, leave an imprint on the cosmic microwave background anisotropy pattern and the rate of growth of large scale structure. The model introduces two new parameters, consisting of the present-day equation of state and the redshift of the freeze-out transition. A Monte Carlo Markov Chain analysis of a ten-dimensional parameter space is performed to compare the model with pre-Planck cosmic microwave background, large scale structure and supernova data and measurements of the Hubble constant. We find that the transition described by this model could have taken place as late as a redshift z~400. We explore the capability of future cosmic microwave background and weak lensing experiments to put tighter constraints on this model. The viability of this model may suggest new directions in dark-energy model building that address the coincidence problem.