arXiv 1809.092412018-09astro-ph.CO

轴子微团簇的早期种子

Early seeds of axion miniclusters

Alejandro Vaquero, Javier Redondo, Julia Stadler

备注：: 57 pages, 26 figures. Version v2 accepted for publication in JCAP
发表信息：: JCAP04(2019)012
DOI：: 10.1088/1475-7516/2019/04/012

摘要：

我们研究的小尺度结构的轴子暗物质在后暴胀的情况下，它预测形成的低质量，高密度的重力束缚的轴子称为轴子微团簇。为此，我们遵循数值宇宙学演化的轴子场和网络的字符串和域壁，直到密度对比被冻结。我们的模拟，包括高达$8192^3$点，是迄今为止提出的非线性政权的轴子场演化的最大的研究。轴子，Klein-Gordon方程的伪呼吸子，在我们的模拟中观察到形成在晚些时候。通过分析和数值计算研究它们的性质，我们观察到，特别是最早期的轴子有助于在微团簇的典型长度尺度上的密度扰动。我们分析了密度场的小尺度结构，给出了相关长度、功率谱和坍缩成轴子微团的高密度区的分布。我们模拟的最终密度场可用于计算包括重力在内的模拟中的微团质量分数。特别是，我们发现，典型的微簇祖细胞比以前认为的要小，只有适度的，$\mathcal{O}(1)$超密度。我们希望这些微团有一个丰富的子结构，出现在弦壁网络的崩溃和轴突产生的小规模波动。

英文摘要：

We study the small scale structure of axion dark matter in the post-inflationary scenario, which predicts the formation of low-mass, high-density clumps of gravitationally bound axions called axion miniclusters. To this end, we follow numerically the cosmological evolution of the axion field and the network of strings and domain walls until the density contrast is frozen. Our simulations, comprising up to $8192^3$ points, are the largest studies of the axion field evolution in the non-linear regime presented so far. Axitons, pseudo-breathers of the Klein-Gordon equation, are observed to form in our simulation at late times. Studying their properties analytically and numerically, we observe that in particular, the earliest axitons contribute to density perturbations at the typical length scale of miniclusters. We analyse the small scale structure of the density field, giving the correlation length, power spectrum and the distribution of high-density regions that will collapse into axion miniclusters. The final density field of our simulations can be used to calculate the minicluster mass fraction in simulations including gravity. In particular, we find that typical minicluster progenitors are smaller than previously thought and only of moderate, $\mathcal{O}(1)$ overdensity. We expect these miniclusters to have a rich sub-structure, emerging from small-scale fluctuations produced in the collapse of the string-wall network and from axitons.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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英文摘要：

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