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arXiv 2203.09396astro-ph.COastro-ph.GAhep-ph
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复标量场暗物质与实超轻轴子的宇宙结构形成:基于CLASS的比较研究

Cosmological structure formation in complex scalar field dark matter versus real ultralight axions: a comparative study using CLASS

Horst Foidl, Tanja Rindler-Daller

AI总结:

本研究修改玻尔兹曼代码CLASS,对比复标量场暗物质(含自相互作用与无自相互作用的模糊暗物质)和实超轻轴子模型的宇宙背景演化与线性结构增长,证实千秒差距核的标量场暗物质模型不受青睐,揭示了两类模型功率谱差异的物理机制。

摘要:

我们延续对ΛSFDM宇宙学的研究,该模型与ΛCDM的区别在于冷暗物质(CDM)被标量场暗物质(SFDM)取代,我们计算了背景宇宙的演化以及线性扰动,重点关注标量模式。我们考虑了具有排斥性四次自相互作用(SI)的复标量场模型,以及无自相互作用的模型,即模糊暗物质(FDM)。为此,我们修改了玻尔兹曼代码CLASS,纳入了复标量场暗物质的物理特性,其特征之一是在极早期宇宙中它的物态方程具有最大刚性,彼时它主导着所有其他宇宙组分,甚至超过辐射。我们计算了多种模型的宇宙微波背景(CMB)和物质功率谱,以及无条件Press-Schechter暗晕质量函数,拓展了此前仅局限于背景研究、或采用忽略早期刚性阶段的半解析方法处理标量场暗物质密度扰动的研究。我们将标量场暗物质和模糊暗物质的结果分别与无自相互作用的实场超轻轴子模型(ULAs)进行比较,刻画了二者各自背景演化和线性结构增长的差异。我们的计算证实了近期文献的已有结果,表明具有千秒差距量级暗晕核的标量场暗物质模型不受青睐,这对它们解释矮星系尺度小尺度问题的能力提出了质疑。我们还发现,复标量场的相位带来的动能导致标量场暗物质/模糊暗物质与超轻轴子模型之间存在显著差异。标量场暗物质功率谱在高波数k处的缓降特征与冷暗物质类似,但背后的物理效应不同:前者源于标量场暗物质的金斯质量快速收缩,后者则源于冷暗物质的梅萨罗斯(Meszaros)效应。此外,我们发现超轻轴子模型功率谱的尖锐截断之后也存在缓降,尽管对应的功率非常小。

英文摘要:

(abridged) We continue the study of $Λ$SFDM cosmologies, which differ from $Λ$CDM in that CDM is replaced by scalar field dark matter (SFDM) by calculating the evolution of the background Universe, as well as linear perturbations, focusing on scalar modes. We consider models with complex scalar field with a repulsive, quartic self-interaction (SI), and models without SI, referred to as fuzzy dark matter (FDM). To this end, we modify the Boltzmann code CLASS, to incorporate the physics of complex SFDM which has as one of its characteristics that its equation of state is maximally stiff in the very early Universe, dominating then over all the other cosmic components, even over radiation. We calculate CMB and matter power spectra as well as unconditional Press-Schechter halo mass functions for various models, expanding previous literature that were limited either to the background, or to a semi-analytical approach to SFDM density perturbations neglecting the early stiff phase. Comparing our results of each, SFDM and FDM, with real-field ultralight axion models (ULAs) without SI, we characterize the differences between the respective background evolution and linear structure growth. Our calculations confirm previous results of recent literature, implying that SFDM models with $\gtrsim$ kpc-size halo cores are disfavored, questioning their ability to explain the small-scale problems on dwarf-galactic scales. Also we find that the kinetic energy due to the phase of the complex field leads to marked differences between SFDM/FDM versus ULAs. The mild falloff in the SFDM power spectrum toward high k is similar to that of CDM but based on different effects, namely the rapidly shrinking Jeans mass for SFDM as opposed to the Meszaros effect for CDM. In addition, we find that the sharp cutoff in the ULA power spectrum is also followed by a mild falloff, albeit at very small power.

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