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arXiv 1503.01235astro-ph.CO
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一个改进的宇宙学模型对具有暗能量尖峰的普朗克数据的拟合

An improved cosmological model fitting of Planck data with a dark energy spike

Chan-Gyung Park

摘要:

$Λ$冷暗物质($Λ\textrm{CDM}$)模型是目前已知的最简单的宇宙学模型,它用最少的参数最好地描述了观测结果。在这里,我们介绍了一个宇宙学模型,是优于传统的$Λ\textrm{CDM}$之一,通过构建暗能量的宇宙学常数$Λ$和额外的流体,被设计成具有极短的瞬态尖峰在能量密度在辐射-物质平等的时代和早期的标度行为与辐射和物质密度的总和。附加流体的密度参数被定义为高斯函数加上对数尺度因子空间中的常数。在存在这种暗能量尖峰的情况下寻找最佳拟合的宇宙学参数,得到的卡方值要小得多,大约是引入的附加参数的5倍,与最佳拟合的$Λ\textrm{CDM}$模型相比,对物质密度和哈勃常数的约束要窄得多。在减少卡方方面的显著改善主要来自于第三($\ell \approx 800$)和第六($\ell \approx 1800$)声学峰周围的普朗克温度功率谱的更好拟合。似然比检验和赤池信息判据表明,相对于传统的$Λ\textrm{CDM}$模型,暗能量尖峰模型更受当前宇宙学观测的青睐.然而,基于惩罚具有更多参数的模型的贝叶斯信息准则,支持暗能量尖峰存在的强有力证据消失。我们的结果强调了在爱因斯坦引力下,同样的观测数据可以用更好的拟合来进行另一种宇宙学参数估计。

英文摘要:

The $Λ$ cold dark matter ($Λ\textrm{CDM}$) model is currently known as the simplest cosmology model that best describes observations with minimal number of parameters. Here we introduce a cosmology model that is preferred over the conventional $Λ\textrm{CDM}$ one by constructing dark energy as the sum of the cosmological constant $Λ$ and the additional fluid that is designed to have an extremely short transient spike in energy density during the radiation-matter equality era and the early scaling behavior with radiation and matter densities. The density parameter of the additional fluid is defined as a Gaussian function plus a constant in logarithmic scale-factor space. Searching for the best-fit cosmological parameters in the presence of such a dark energy spike gives a far smaller chi-square value by about five times the number of additional parameters introduced and narrower constraints on matter density and Hubble constant compared with the best-fit $Λ\textrm{CDM}$ model. The significant improvement in reducing chi-square mainly comes from the better fitting of Planck temperature power spectrum around the third ($\ell \approx 800$) and sixth ($\ell \approx 1800$) acoustic peaks. The likelihood ratio test and the Akaike information criterion suggest that the model of dark energy spike is strongly favored by the current cosmological observations over the conventional $Λ\textrm{CDM}$ model. However, based on the Bayesian information criterion which penalizes models with more parameters, the strong evidence supporting the presence of dark energy spike disappears. Our result emphasizes that the alternative cosmological parameter estimation with even better fitting of the same observational data is allowed in the Einstein's gravity.

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