论文标题
反事实宇宙中的重子的命运
The fate of baryons in counterfactual universes
论文作者
论文摘要
我们提出了九个模拟的结果，这些模拟将标准$λ$冷的暗物质宇宙学（$λ$ cdm）与反事实宇宙进行了比较，使用ENZO仿真代码，大约$ 100 \，{\ rm gyr} $。我们改变了$λ$的值以及探索对光晕质量函数（HMF），播层间介质（IGM）和星形形成历史（SFH）进化的影响的波动幅度。恒星形成速率密度（SFRD）的独特峰及其随后的下降都受重力吸引力与$λ$的加速效应之间的相互作用的影响。 IGM在较大$λ$的型号和较低$σ_8$的型号中更快地冷却，反映了与这些变化相关的减少的SFRD - 尽管更改$σ_8$并不随着$λ$而变化，而不是与Igm的热历史相关的$λ$。但是，这些诱导的对IgM或电离背景的变化对计算出的SFRD几乎没有影响。我们为SFRD在这些不同的宇宙中的演变提供了拟合，我们会随着时间的推移整合，以得出渐近星形成效率。连同温伯格在$λ$上的统一之前，观察者经历$λ$的估计概率没有比观察到的值大于13％，比某些替代性估计值大得多。然后，在Enzo模型框架内，多元宇宙中的观察者选择能够从统计上说明宇宙常数的较小价值，尽管我们宇宙中的$λ$似乎确实位于预测范围的低端。
We present results from nine simulations that compare the standard $Λ$ Cold Dark Matter cosmology ($Λ$CDM) with counterfactual universes, for approximately $100\,{\rm Gyr}$ using the Enzo simulation code. We vary the value of $Λ$ and the fluctuation amplitude to explore the effect on the evolution of the halo mass function (HMF), the intergalactic medium (IGM) and the star formation history (SFH). The distinct peak in star formation rate density (SFRD) and its subsequent decline are both affected by the interplay between gravitational attraction and the accelerating effects of $Λ$. The IGM cools down more rapidly in models with a larger $Λ$ and also with a lower $σ_8$, reflecting the reduced SFRD associated with these changes -- although changing $σ_8$ is not degenerate with changing $Λ$, either regarding the thermal history of the IGM or the SFH. However, these induced changes to the IGM or ionizing background have little impact on the calculated SFRD. We provide fits for the evolution of the SFRD in these different universes, which we integrate over time to derive an asymptotic star formation efficiency. Together with Weinberg's uniform prior on $Λ$, the estimated probability of observers experiencing a value of $Λ$ no greater than the observed value is 13%, substantially larger than some alternative estimates. Within the Enzo model framework, then, observer selection within a multiverse is able to account statistically for the small value of the cosmological constant, although $Λ$ in our universe does appear to be at the low end of the predicted range.
