Bright High z SnIa：对LCDM的挑战？
Bright High z SnIa: A Challenge for LCDM?
摘要：
最近，Kowalski et. al.（arxiv：0804.4142）指出，“在z> 1处，SnIa数据有一个出乎意料的亮度”。我们通过构建一个新的统计量，这是直接适用于Ia型超新星（SnIa）的距离模数量化这一声明。这个统计量的目的是拿起系统的亮度趋势的SnIa数据点相对于一个最适合的宇宙学模型在高红移。它基于在特定宇宙学模型（例如LCDM）的背景下，将SnIa距离模量与相应的最佳拟合值之间的归一化差异进行分箱。然后，我们专注于最高的红移仓，并将其大小向较低的红移扩展，直到仓归一化差（BND）在红移z_c（仓大小N_c）处改变符号（交叉0）。然后将该交叉的箱大小N_c（统计变量）与基于最佳拟合模型的蒙特卡罗数据实现的相应交叉箱大小N_{mc}进行比较。我们发现，相对于最佳拟合LCDM模型，从Union 08和Gold 06数据中获得的交叉箱大小N_c与从最佳拟合LCDM中获得的相应蒙特卡罗数据集的N_{mc}相比异常大。特别是，只有2.2%的Monte Carlo LCDM数据集与Gold 06的N_c值一致，而Union 08的N_c值的相应概率为5.3%。因此，根据这一统计，在（w_0，w_1）=（-1，0）模型（LCDM宇宙学）的背景下，Union 08和Gold 06数据集的高红移亮度偏差被实现的概率小于6%。对于Union 08和Gold 06数据集，在（w_0，w_1）=（-1.4，2）模型的上下文中，相应的实现概率都超过30%。
英文摘要：
It has recently been pointed out by Kowalski et. al. (arxiv:0804.4142) that there is `an unexpected brightness of the SnIa data at z>1'. We quantify this statement by constructing a new statistic which is applicable directly on the Type Ia Supernova (SnIa) distance moduli. This statistic is designed to pick up systematic brightness trends of SnIa datapoints with respect to a best fit cosmological model at high redshifts. It is based on binning the normalized differences between the SnIa distance moduli and the corresponding best fit values in the context of a specific cosmological model (eg LCDM). We then focus on the highest redshift bin and extend its size towards lower redshifts until the Binned Normalized Difference (BND) changes sign (crosses 0) at a redshift z_c (bin size N_c). The bin size N_c of this crossing (the statistical variable) is then compared with the corresponding crossing bin size N_{mc} for Monte Carlo data realizations based on the best fit model. We find that the crossing bin size N_c obtained from the Union08 and Gold06 data with respect to the best fit LCDM model is anomalously large compared to N_{mc} of the corresponding Monte Carlo datasets obtained from the best fit LCDM in each case. In particular, only 2.2% of the Monte Carlo LCDM datasets are consistent with the Gold06 value of N_c while the corresponding probability for the Union08 value of N_c is 5.3%. Thus, according to this statistic, the probability that the high redshift brightness bias of the Union08 and Gold06 datasets is realized in the context of a (w_0,w_1)=(-1,0) model (LCDM cosmology) is less than 6%. The corresponding realization probability in the context of a (w_0,w_1)=(-1.4,2) model is more than 30% for both the Union08 and the Gold06 datasets.
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