Test of the Cosmic Transparency with the Baryon Acoustic Oscillation and Type Ia Supernova Data

We use the latest baryon acoustic oscillation and Union 2.1 type Ia supernova data to test the cosmic opacity between different redshift regions without assuming any cosmological models. It is found that the universe may be opaque between the redshift regions 0.35 0.44, 0.44 0.57 and 0.6-0.73 since the best fit values of cosmic opacity in these regions are positive, while a transparent universe is favored in the redshift region 0.57-0.63. However, in general, a transparent universe is still consistent with observations at the lo confidence level.

Constraints from Type Ia supernovae on the Λ-CDM model in Randers-Finsler space

Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann equation and a new luminosity distance-redshift relation is proposed. A best-fit to the Type Ia supernovae （SNe） observations yields that the Λ in the Λ-CDM model is suppressed to almost zero. This fact indicates that the astronomical observations on the Type Ia SNe can be described well without invoking any form of dark energy. The best-fit age of the universe is given. It is in agreement with the age of our galaxy.

A Model of Accelerated Expansion of the Universe Based on the Idea about a Hypothetical 4-Dimensial Substance with an Inverse Population of Energy Levels

Based on the idea of hypothetical 4-dimensial substance with an inverse population of energy levels, a model of accelerated expansion of the Universe has been developed, which describes Hubble diagrams with great accuracy for type Ia supernovae, quasars and gamma-ray burst sources at the Hubble parameter value of 67.7 km/s/Mpc, coinciding with the value obtained from analysis of inhomogeneities of relic radiation. Calculations at the Hubble parameter value of 73.5 km/s/Mpc, obtained using the ΛCDM model based on the analysis of data on type Ia supernovae and cepheids, differ markedly from the observed data. An explanation of the two values of the Hubble constant is proposed. It is shown that in this model, the magnitude of 13.8 billion years characterizes not the age of the Universe, but the time of propagation of light from those galaxes whose acceleration of removal has a minimal value. Based on the recently discovered curvature of the Universe, estimates are given of the lower limits of its size and lifetime, which turned out to be at least 270 billon years. The probability of transition from the excited state to the underlying energy levels of a hypothetical 4-dimensial substance, as well as the low of increasing energy density as a result of transitions to the underlying levels of this substance, is determined.

Non-parametric reconstruction of dark energy and cosmic expansion from the Pantheon compilation of type Ia supernovae

The equation of state(EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise constraint on the EoS of dark energy can be obtained. In this study, we reconstruct the EoS of dark energy and cosmic expansion using Gaussian processes(GP) from the most up-to-date Pantheon compilation of type Ia supernovae(SNe Ia),which consists of 1048 finely calibrated SNe Ia. The reconstructed EoS of dark energy has a large uncertainty owing to its dependence on the second-order derivative of the construction. Adding the direct measurements of Hubble parameters H(z) as an additional constraint on the first-order derivative can partially reduce the uncertainty;however, it is still not sufficiently precise to distinguish between the evolving and the constant dark energy. Moreover, the results heavily rely on the prior of the Hubble constant H0. The H0 value inferred from SNe+ H(z) without prior is H0= 70.5 ± 0.5 km s^-1 Mpc^-1. Moreover, the matter density ΩM has a non-negligible effect on the reconstruction of dark energy. Therefore, more accurate determinations on H0 and ΩM are required to tightly constrain the EoS of dark energy.

Ia 超新星的几个问题(英文)

首先利用Ａｓｉａｇｏ 超新星星表对Ｉａ 超新星作了统计分析。其次用具有精确测光的Ｉａ 超新星对其均匀性及多样性进行了研究。旋涡星系中Ｉａ 超新星的产生率比椭圆星系的要高。最亮的Ｉａ 超新星只出现于晚型旋涡星系中；而旋涡星系及早型的椭圆星系都是暗Ｉａ 超新星的寄主星系。离星系中心越近Ｉａ 超新星的光度弥散有增加的趋势，但这一趋势对蓝Ｉａ 超新星不明显。利用色指数可将Ｉａ 超新星划分为蓝超新星及红超新星。蓝Ｉａ 超新星构成了相对均匀的Ｉａ 超新星样本，是较好的距离指示器；而红Ｉａ 超新星的存在则表明了Ｉａ 超新星整体多样性的特点。最后，我们还探讨了Ｉａ 超新星中碳点火的非线性问题。

Ia超新星对变化暗能量模型的限制

最近Wetterich给出了一个简单的参数化的w(z)=(1+w0)/(1+bln(1+z))来表示一个变化的暗能量模型,本文利用194Ia超新星的观测数据对这一暗能量模型进行了检验。我们发现Ia超新星偏爱w(z)不变的Phantom宇宙,并且在95.4%的可能性上我们可以排除?m0>0.6和w0>?0.5的分布区域。

Ia型超新星测距揭示宇宙的命运——2011年诺贝尔物理学奖简介

2011年度诺贝尔物理学奖授予了在天体物理研究领域取得杰出成就的美国科学家索尔.波尔马特、拥有美国和澳大利亚双重国籍的科学家布赖恩.施密特以及美国科学家亚当.里斯。他们通过Ia型超新星测距发现宇宙的膨胀是加速的,从而揭示了暗能量的存在。笔者将对人类认识宇宙的过程、Ia型超新星与宇宙加速膨胀、暗能量以及Ia型超新星研究中存在的问题做全面的介绍,并介绍中国学者在该领域的研究进展。文章的最后做了展望。

A critique of supernova data analysis in cosmology

Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high-quality supernovae data-sets are being produced, their statistical anal- ysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.

不透明度对Ia超新星极大光度的影响

在Arnett’s rule基础上,通过考察Ia超新星光极大时的物理情形,计算修正因子,并讨论不透明对修正因子的影响.结论表明用Arnett’s rule估计出的Ia超新星光极大时的光度(观测光度)偏低,在一定条件下修正因子对极大时的光度有重要影响.

基于Ia型超新星理论的哈勃常数

模拟Ia型超新星光球层膨胀过程,结合当前观测事实,计算哈勃常数范围为54.25-77.00 km/(s.Mpc),典型值约为64.25 km(s.Mpc),与观测分析结果基本一致.

Variable Speed of Light with Time and General Relativity

In a previous article entitled: “Evidences for varying speed of light with time” [1], a series of observational evidence was presented in favor of the hypothesis that the speed of light varies with time according to the relationship dc/dt = -Hc, where H is the Hubble constant which is considered a universal constant. In this paper we propose to elaborate on the observational evidence supporting the hypothesis, and to probe the consequences of this relationship on General Relativity. Also we will provide a theoretical justification of the previous relationship and we will show how from it we can deduce galactic velocity curves. We can deduce the important empirical Tully-Fisher relation linking these curves to the baryonic mass of the galaxy and we can justify the apparent accelerated expansion of the universe without intervening elusive entities such as dark matter and dark energy.

超新星的最新统计分析

用最新的Asiago超新星星表和RC3星系表分析了各类超新星在不同哈勃型星系中的分布；考虑Ⅰa型超新星的峰值光度同光变曲线下降率的关系后，得出的哈勃常数值误差较小，表明近星系Ⅰa型超新星仍是一个较好的距离指示器；分析了高红移超新星同宇宙学的紧密联系．

Constraints on Dark Energy Models from Weak Gravity Conjecture

We study the constraints on the dark energy model with constant equation of state parameter w = pip and the holographic dark energy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives tu 〈 -0.7 at the 3σ confidence level. The holographic dark energy model realized by a scalar field is in swampland.

Consistency of Pantheon+supernovae with a large-scale isotropic universe

We investigate the possible anisotropy of the universe using data on the most up-to-date type Ia supernovae,i.e.,the Pantheon+compilation.We fit the full Pantheon+data with the dipole-modulated ΛCDM model and find that the data are well consistent with a null dipole.We further divide the full sample into several subsamples with different high-redshift cutoffs zc.It is shown that the dipole appears at the 2σ confidence level only if z_(c)≤0.1,and in this redshift region,the dipole is very stable,almost independent of the specific value of zc.For z_(c)=0.1,the dipole amplitude is D=1.0_(-0.4^(+0.4))×10^(-3),pointing toward(l,b)=(334.5°_(-21.6°)^(+25.7°),16.0°_(-16.8°)^(+27.1°)),which is approximately 65°away from the CMB dipole.This implies that the full Pantheon+sample is consistent with a large-scale isotropic universe,but the low-redshift anisotropy could not be purely explained by the peculiar motion of the local universe.

Evidences for Varying Speed of Light with Time

Aims: The paper explores the hypothesis that the speed of light c is decreasing over time at rate (dc/dt)=-H? c, H being the Hubble constant. This hypothesis differs from the so-called tired light, in which the velocity c is supposed to vary during the journey of photons in the empty space for some frictional mechanism. In the hypothesis of the author the speed c, during this journey, is assumed constant. In this way the problems of the tired hypothesis are overcome. Methods: The paper links the variation dc/dt with the Hubble constant and infers a value of dc/dt from the difference between the value of the variation of the Earth-Moon distance measured by the Lunar Laser Ranging Experiment and the tidal effect. Results: Under the hypothesis c time varying, we explain: 1) The cosmological redshift. 2) The anomalous acceleration ap ≈ -8 × 10-10 m?sec-2, measured for some spacecrafts. 3) The high redshift of supernovae Ia, which seems to evidence an acceleration of the expansion of the universe. 4) The peripheral motion of stars in galaxies around their rotational centre. 5) The dilation of the light curves observed for supernovae Ia.

How a Realistic Linear <i>R_h= ct </i>Model of Cosmology Could Present the Illusion of Late Cosmic Acceleration

Realistic FLRW cosmic coasting models which contain matter now appear to be a reasonable alternative in explaining the accumulated Supernova Cosmology Project data since 1998. In sharp contrast to the unrealistic original classic Milne universe, which was entirely devoid of matter, these modified Milne-type models containing matter, often referred to as realistic linear Rh = ct models, have rapidly become the primary competition with standard cosmology. This paper compares the expected relative luminosity distances and relative angular diameter distances for given magnitudes of redshift within these two competing models. A simple ratio formula is derived, which explains how expected luminosity distances and angular diameter distances for given magnitudes of redshift within a realistic Milne-type cosmic expansion could create the illusion (for standard model proponents) of cosmic acceleration where none exists.

Observation Constraints on the Simplified GCG Model

A simplified version of generalized Chaplygin gas （GCG） as a dark energy model is studied. By using the latest 162 ESSENCE type Ia supernovae （She Ia） data, 30 high redshift She Ia data, the baryonic acoustic oscillation peak from SDSS and the CMB data from WMAP3, a strong constraint on this simplified GCG model is obtained. At the 95.4% confidence level we obtain 0.21 ≤ Ωm ≤ 0.31 and 0.994 〈 α 〈 1.0 with the best fit Ωm = 0.25 and a = 1. This best fit scenario corresponds to an accelerating universe with qo ≈-0.65 and z ≈ 0.81 （a redshiR of cosmic phase transition from deceleration to acceleration）.

距离阶梯与哈勃常数危机

哈勃常数是天文学中的一个重要参数.当前最前沿的两项观测证据在哈勃常数上出现了5倍标准差的差异,即“哈勃常数危机”.本文总结了基于距离阶梯测量哈勃常数方法中的几种常用量天尺,包括几何距离、造父变星、红巨星顶点恒星和Ia型超新星;分析了它们的优缺点、潜在问题以及未来的优化预期.同时,介绍了几种潜在的量天尺.它们能帮助检查常用量天尺并独立测量哈勃常数.未来五年内,随着Gaia DR4的释放和视差零点的优化、詹姆斯韦伯望远镜的数据累积、中国空间站巡天望远镜的发射和观测及数据释放,天文学家将有望给出当前“哈勃常数危机”的答案.

Exploring the latest Pantheon SN Ia dataset by using three kinds of statistics techniques

In this work,we explore the cosmological consequences of the latest Type Ia supernova(SN Ia)dataset,Pantheon,by adopting the wCDM model.The Pantheon dataset currently contains the largest number of SN Ia samples,which contains 1048 supernovae on the redshift range 0<z<2.3.Here we take into account three kinds of SN Ia statistics techniques,including:(1)magnitude statistics(MS),which is the traditional SN Ia statistics technique;(2)flux statistics(FS),which is based on the flux-averaging(FA)method;and(3)improved flux statistics(IFS),which combines the advantages of MS and FS.It should be mentioned that the IFS technique needs to scan the(zcut,Δz)parameters plane,where zcut andΔz are redshift cut-off and redshift interval of FA,respectively.The results are as follows.(1)Using the SN dataset only,the best FA recipe for IFS is(zcut,Δz)=(0.1,0.08);(2)comparing to the old SN dataset,JLA,adopting the Pantheon dataset can reduce the 2σerror bars of equation of state w by 38%,47%and 53%for MS,FS and IFS,respectively;(3)FS gives closer results to other observations,such as Baryon acoustic oscillations and cosmic microwave background;(4)compared with FS and IFS,MS more favors a Universe that will end in a‘big rip’.

Revisit of constraints on holographic dark energy:SNLS3 dataset with the effects of time-varying β and different light-curve fitters

Previous studies have shown that for the Supernova Legacy Survey three-year （SNLS3） data there is strong evidence for the redshifl- evolution of color-luminosity parameter β of type Ia supernovae （SN Ia）. In this paper, we explore the effects of varying β on the cosmological constraints of holographic dark energy （HDE） model. In addition to the SNLS3 data, we also use Planck distance prior data of cosmic microwave background （CMB）, as well as galaxy clustering （GC） data extracted from Sloan Digital Sky Survey （SDSS） data release 7 and Baryon Oscillation Spectroscopic Survey （BOSS）. We find that, for the both cases of using SN data alone and using SN＋CMB＋GC data, involving an additional parameter of β can reduce χ^2 by - 36; this shows that β deviates from a constant at 6σ- confidence levels. Adopting SN＋CMB＋GC data, we find that compared to the constant β case, varying β yields a larger fractional matter density Ωm0 and a smaller reduced Hubble constant h; moreover, varying β significantly increases the value of HDE model parameter c, leading to c ≈ 0.8, consistent with the constraint results obtained before Planck. These results indicate that the evolution of β should be taken into account seriously in the cosmological fits. In addition, we find that relative to the differences between the constant β and varying β（z） cases, the effects of different light-curve fitters on parameter estimation are very small.