类共形年龄长度表征的全息暗能量模型的宇宙学约束与分析
Cosmological Constraint and Analysis on Holographic Dark Energy Model Characterized by the Conformal-age-like Length
摘要：
我们提出了一个最佳拟合分析的单参数全息暗能量模型，其特征在于共形年龄的长度，$L=\frac{1}{a^4(t)}\int_0^tdt' a^3(t') $。基于Union 2对557颗Ia超新星的资料汇编，SDSS DR 7的重子声振荡结果和WMAP 7的宇宙微波背景辐射资料，我们证明了该模型给出的最小$χ^2_{min}=546.273$与$Λ$ CDM模型的$χ^2_{Λ{\rm CDM}}=544.616$相当.模型中涉及的单参数$d$为$d=0.232\pm 0.006\pm 0.009$。由于暗能量$Ω_{de}\sim d^2a^2$在$a \ll 1$的分数密度，暗能量的分数在早期宇宙中自然是可以忽略的，$Ω_{de} \ll 1$在$a \ll 1$。对物质的分数能量密度和状态方程的约束分别为$Ω_{m0}=0.286^{+0.019}_{-0.018}^{+0.032}_{-0.028}$和$w_{de0}=-1.240^{+0.027}_{-0.027}^{+0.045}_{-0.044}$。与$Λ$ CDM模型相比，该模型导致物质的比例略大。系统地分析了暗能量的分数能量密度、暗能量的状态方程、减速参数和状态探测器等的宇宙演化。注意到状态方程从$w_{de}>-1$过渡到$w_{de}<-1$，宇宙最近从减速膨胀（$q>0$）过渡到加速膨胀（$q<0$），状态发现器可以作为区分CHDE模型和$Λ$ CDM模型的敏感诊断。
英文摘要：
We present a best-fit analysis on the single-parameter holographic dark energy model characterized by the conformal-age-like length, $L=\frac{1}{a^4(t)}\int_0^tdt' a^3(t') $. Based on the Union2 compilation of 557 supernova Ia data, the baryon acoustic oscillation results from the SDSS DR7 and the cosmic microwave background radiation data from the WMAP7, we show that the model gives the minimal $χ^2_{min}=546.273$, which is comparable to $χ^2_{Λ{\rm CDM}}=544.616$ for the $Λ$CDM model. The single parameter $d$ concerned in the model is found to be $d=0.232\pm 0.006\pm 0.009$. Since the fractional density of dark energy $Ω_{de}\sim d^2a^2$ at $a \ll 1$, the fraction of dark energy is naturally negligible in the early universe, $Ω_{de} \ll 1$ at $a \ll 1$. The resulting constraints on the present fractional energy density of matter and the equation of state are $Ω_{m0}=0.286^{+0.019}_{-0.018}^{+0.032}_{-0.028}$ and $w_{de0}=-1.240^{+0.027}_{-0.027}^{+0.045}_{-0.044}$ respectively. The model leads to a slightly larger fraction of matter comparing to the $Λ$CDM model. We also provide a systematic analysis on the cosmic evolutions of the fractional energy density of dark energy, the equation of state of dark energy, the deceleration parameter and the statefinder. It is noticed that the equation of state crosses from $w_{de}>-1$ to $w_{de}<-1$, the universe transits from decelerated expansion ($q>0$) to accelerated expansion ($q<0$) recently, and the statefinder may serve as a sensitive diagnostic to distinguish the CHDE model with the $Λ$CDM model.
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