In this work, by applying the redshift tomography method to Joint Light-curve Analysis (JLA) supernova sample, we explore the possible redshift-dependence of stretch-luminosity parameter $α$ and color-luminosity parameter $β$. The basic idea is to divide the JLA sample into different redshift bins, assuming that $α$ and $β$ are piecewise constants. Then, by constraining the $Λ$CDM model, we check the consistency of cosmology-fit results given by the SN sample of each redshift bin. We also adopt the same technique to explore the possible evolution of $β$ in various subsamples of JLA. Using the full JLA data, we find that $α$ is always consistent with a constant. In contrast, at high redshift $β$ has a significant trend of decreasing, at $\sim 3.5σ$ confidence level (CL). Moreover, we find that low-$z$ subsample favors a constant $β$; in contrast, SDSS and SNLS subsamples favor a decreasing $β$ at 2$σ$ and $3.3σ$ CL, respectively. Besides, by using a binned parameterization of $β$, we study the impacts of $β$'s evolution on parameter estimation. We find that compared with a constant $β$, a varying $β$ yields a larger best-fit value of fractional matter density $Ω_{m0}$, which slightly deviates from the best-fit result given by other cosmological observations. However, for both the varying $β$ and the constant $β$ cases, the $1σ$ regions of $Ω_{m0}$ are still consistent with the result given by other observations.
In this work, we explore the cosmological consequences of the "Joint Light-curve Analysis" (JLA) supernova (SN) data by using an improved flux-averaging (FA) technique, in which only the type Ia supernovae (SNe Ia) at high redshift are flux-averaged. Adopting the criterion of figure of Merit (FoM) and considering six dark energy (DE) parameterizations, we search the best FA recipe that gives the tightest DE constraints in the $(z_{cut}, Δz)$ plane, where $z_{cut}$ and $Δz$ are redshift cut-off and redshift interval of FA, respectively. Then, based on the best FA recipe obtained, we discuss the…
The case of SN Ia Hubble diagrams from photometrically selected samples using photometric SN host galaxy redshifts is investigated. The host redshift uncertainties and the contamination by core collapse SNe are addressed. As a test, we use the 3-year photometric SN Ia sample of the SuperNova Legacy Survey (SNLS), made of 437 objects between 0.1 and 1.05 in redshift. We combine this sample with non-SNLS objects of the JLA spectroscopic sample, made of 501 objects mostly below 0.4 in redshift. We study two options for the origin of the redshifts of the photometric sample, either provided entirel…
The cosmological principle asserts that the Universe looks spatially homogeneous and isotropic on sufficiently large scales. Given the fundamental implications of the cosmological principle, it is important to empirically test its validity on various scales. In this paper, we use the Type Ia supernova (SN~Ia) magnitude-redshift relation, from both the Pantheon and JLA compilations, to constrain theoretically motivated anisotropies in the Hubble flow. In particular, we constrain the quadrupole moment in the effective Hubble parameter and the dipole moment in the effective deceleration parameter…
Present Day Cosmic Acceleration from SDSS and DESI BAO: A Call for Finer Tomography of the DESI Bright Galaxy Survey
Physics Department and INFN, Università di Roma “La Sapienza”（罗马大学物理系和意大利国家核物理研究所）；Departamento de Física Fundamental and IUFFyM, Universidad de Salamanca（萨拉曼卡大学基础物理系和统一场与量子物质研究院）
The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: Angular clustering tomography and its cosmological implications
我们调查的宇宙学意义的研究星系聚类使用层析成像的方法应用到最终的BOSS DR 12星系样本，包括自动和交叉的红移壳层之间的关联函数。我们使用最先进的非线性、偏置和红移空间失真模型，在红移仓中对角关联函数$ω(θ)$的完整形状的信号进行建模。我们目前的结果的红移演化的线性偏差的BOSS星系，这是不能得到与传统的方法进行星系聚类分析。我们还得到宇宙学参数的约束，结合这种层析分析与测量的宇宙微波背景（CMB）和Ia型超新星（SNIa）。我们探讨了一些宇宙学模型，包括标准的$Λ$ CDM模型及其最有趣的扩展，如偏离$w_\rm{DE} = -1$，非最小中微子质量，空间曲率和偏离广义相对论使用的增长指数$γ$ parametrisation。一般来说，这些结果可以与当今最精确的宇宙学参数约束相媲美，并且与标准模型非常吻合。特别是，结合CMB，$ω(θ)$和SNIa，我们发现一个值的$w_\rm{DE}$一致的$-1$的精度优于5\%时，它被假定为在时间上是恒定的，当我们也允许一个空间弯曲的宇宙时，优于6\%。
Exploring the full parameter space for an interacting dark energy model with recent observations including redshift-space distortions: Application of the parametrized post-Friedmann approach
暗能量可以改变暗物质的动力学，如果它们之间存在直接的相互作用。因此，测量结构生长，例如，红移空间畸变（RSD）是一个强有力的工具来约束相互作用暗能量（IDE）模型。对于广泛研究的$Q=3βHρ_{de}$模型，以前的工作表明，只有一个非常小的耦合（$β\sim\mathcal{O}(10^{-3})$）可以生存在目前的RSD数据。然而，由于IDE情景中存在大规模不稳定性，所有这些分析都必须假设$w>-1$和$β>0$。在我们最近的工作[Phys. Rev. D 90，063005（2014）]中，我们通过为IDE场景建立参数化后弗里德曼（PPF）框架，成功解决了这个大规模不稳定性问题。因此，我们第一次有能力探索IDE模型的完整参数空间。在这项工作中，我们重新审视的观测约束的PPF框架内的$Q=3βHρ_{de}$模型。利用普朗克数据、重子声学振荡数据、超新星JLA样本和哈勃常数测量，得到了$β=-0.010^{+0.037}_{-0.033}$（$1σ$）。在分析中进一步合并RSD数据后，拟合结果变为$β=-0.0148^{+0.0100}_{-0.0089}$（$1σ$）。借助于RSD数据，$β$的误差大大减小。与以往的结果相比，我们的结果表明，一个负的$β$是有利的，目前的观测，并允许相对较大的相互作用率由目前的RSD数据。
