标题： 关于暴胀和慢收缩初始条件的概率 显示英文标题

标题： On the Probability of the Initial Conditions for Inflation and Slow Contraction

摘要： 一些基于数值相对论模拟的最新研究声称，缓慢收缩/外爆在使宇宙进入我们今天在大尺度上观察到的均匀、各向同性和平坦状态的平滑机制方面被强烈偏好于暴胀。 在本文中，我们通过估计在暴胀或外爆开始时主导宇宙的自由标量场在与当时哈勃半径相当的尺度上足够均匀的概率，来评估上述模拟中使用的初始条件的可能性。 我们探索了表征标量场初始功率谱的参数空间，发现对于固定的参数选择，其中一种可能性可能比另一种更高。 另一方面，当我们对这些参数进行极值化时，我们发现暴胀的最大概率远高于外爆。 显示英文摘要

摘要： Some recent studies based on numerical relativity simulations claim that slow contraction/ekpyrosis is strongly preferred over inflation as the smoothing mechanism that brought the universe into the homogeneous, isotropic and flat state we observe today on large scales. In this paper, we evaluate the likelihood of the initial conditions employed in the aforementioned simulations by estimating the probability that a free scalar field dominating the universe at the beginning of inflation or ekpyrosis will be sufficiently homogeneous on scales comparable to the Hubble radius at that time. We explore the space of parameters that characterize the initial power spectrum of the scalar field, finding that either can be more likely than the other for a fixed choice of parameters. On the other hand, when we extremize over these parameters, we find that the maximal probability for inflation is much higher than that of ekpyrosis.