碰撞less相对论气体的宇宙学演化作为暗物质
Cosmological evolution of collisionless relativistic gases as dark matter
AI总结：
该研究提出了一种基于无碰撞相对论动能气体的暗物质模型，通过与普朗克2018 CMB数据对比，发现小β值与ΛCDM观测一致，而较大β值则受限于早期相对论效应。
摘要：
我们研究了一种现象学暗物质模型，该模型被描述为一个无碰撞的相对论性动能气体，在一个空间平坦的弗里德曼-勒梅特-罗伯逊-沃克宇宙中。在归一化到观测到的现在暗物质丰度之后，该模型由一个无量纲参数β完全指定，该参数被解释为现在粒子速度以光速为单位。由此得到的能量密度、压力和声速允许闭合的解析表达式，介于早期时间的辐射状状态和晚期时间的冷暗物质之间。我们将该模型实施在CLASS代码的修改版本中，并将其与普朗克2018 CMB数据进行对比。我们发现足够小的β值在观测上与ΛCDM无法区分，而较大的β值在早期时间引起相对论效应则受到限制。这些结果证实了相对论性动能气体情景与当前宇宙学观测的一致性。
英文摘要：
We study a phenomenological dark matter model described as a collisionless relativistic kinetic gas in a spatially flat Friedmann-Lemaître-Robertson-Walker universe. After normalization to the observed present-day dark matter abundance, the model is fully specified by a single dimensionless parameter $β$, interpreted as the present particle velocity in units of the speed of light. The resulting energy density, pressure, and sound speed admit closed analytic expressions, interpolating between a radiation-like regime at early times and cold dark matter at late times. We implement the model in a modified version of the Boltzmann code CLASS and confront it with Planck 2018 CMB data. We find that sufficiently small values of $β$ are observationally indistinguishable from $Λ$CDM, while larger values inducing relativistic effects at early times are constrained. These results establish the consistency of the relativistic kinetic gas scenario with current cosmological observations.
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