论文标题
高红移宇宙学:辅助变量与帕德多项式
High-redshift cosmography: auxiliary variables versus Padé polynomials
论文作者
论文摘要
当宇宙数据跨度超出红移限制$ z \ simeq1 $时,宇宙学变得非预测。这导致\ emph {强收敛问题}危害其生存能力。在这项工作中,我们批判性地比较了融合问题的两个主要解决方案,即红移的$ y $ parametrizations和基于Padé系列的Taylor扩展的替代方案。特别是,在几种可能性中,我们考虑了两个广泛采用的参数化,即$ y_1 = 1-a $和$ y_2 = \ arctan(a^{ - 1} -1)$,是$ $ a $ a $ a的比例因子。我们发现$ y_2 $ -parametrization的性能要比整个红移域上的$ y_1 $ parametrization相对较好。即使$ y_2 $克服了$ y_1 $的问题,我们也会发现,亮度距离$ d_l(z)$的最可行的近似值是根据padé近似来给出的。为了通过宇宙数据检查此结果,我们将padé近似值分析至第五阶,并将这些系列与相同订单的相应$ y $变量进行比较。我们研究了两个不同的领域,涉及Pantheon Superovae IA数据的蒙特卡洛分析,$ H(z)$和移位参数测量。我们得出的结论是,(2,1)padé近似是统计学上解释低和高还原数据的最佳方法,以及第五阶$ y_2 $ -parametrization。在高红移下,(3,2)帕德近似不能完全排除,而(2,2)帕德一基本上被排除在外。
Cosmography becomes non-predictive when cosmic data span beyond the red shift limit $z\simeq1 $. This leads to a \emph{strong convergence issue} that jeopardizes its viability. In this work, we critically compare the two main solutions of the convergence problem, i.e. the $y$-parametrizations of the redshift and the alternatives to Taylor expansions based on Padé series. In particular, among several possibilities, we consider two widely adopted parametrizations, namely $y_1=1-a$ and $y_2=\arctan(a^{-1}-1)$, being $a$ the scale factor of the Universe. We find that the $y_2$-parametrization performs relatively better than the $y_1$-parametrization over the whole redshift domain. Even though $y_2$ overcomes the issues of $y_1$, we get that the most viable approximations of the luminosity distance $d_L(z)$ are given in terms of Padé approximations. In order to check this result by means of cosmic data, we analyze the Padé approximations up to the fifth order, and compare these series with the corresponding $y$-variables of the same orders. We investigate two distinct domains involving Monte Carlo analysis on the Pantheon Superovae Ia data, $H(z)$ and shift parameter measurements. We conclude that the (2,1) Padé approximation is statistically the optimal approach to explain low and high-redshift data, together with the fifth-order $y_2$-parametrization. At high redshifts, the (3,2) Padé approximation cannot be fully excluded, while the (2,2) Padé one is essentially ruled out.