In this work, we present comprehensive observational constraints on the time-varying vacuum Lambda(t)CDM cosmology using the latest baryon acoustic oscillation (BAO) data from Dark Energy Spectroscopic Instrument (DESI) Data Release 2 measurements in combination with cosmic chronometer H(z) data. We explicitly quantify the impact of vacuum dynamics on the expansion history, the total effective equation of state parameter of the unified cosmic fluid, the effective dark energy equation of state parameter, and the deceleration parameter in the spatially flat Lambda(t)CDM model. We perform a full Markov Chain Monte Carlo (MCMC) analysis and statistical model comparison, providing a consistent assessment of the Lambda(t)CDM model relative to the standard LambdaCDM framework. Our results demonstrate that H(z) and BAO observations strongly constrain deviations from the LambdaCDM model, driving the vacuum dynamics parameter alpha toward zero, while significantly reducing parameter degeneracies and alleviating the Hubble tension.
A New Consistency Test for the $Λ$CDM Model using Radial and Transverse BAO Measurements
The International Division of the Second High School Attached to Beijing Normal University（北京师范大学第二附属中学国际部）；Department of Astronomy, Tsinghua University（清华大学天文系）
We study the statistics of various large-scale structure tracers in gravity-only cosmological simulations including baryons and cold dark matter (CDM) initialized with two different transfer functions, and simulated as two distinct fluids. This allows us to study the impact of baryon-CDM relative perturbations on these statistics. In particular, we focus on the statistics of cosmic voids, as well as on the matter and halo real-space 2-point correlation function and baryon acoustic oscillations (BAO) peak. We find that the void size function is affected at the 1-2% level at maximum, and that th…
In this paper, the CMB/BAO measurements which cover the 13 redshift data in the regime $0.106 \leq z \leq 2.34$ are given out. The CMB/BAO samples are based on the BAO distance ratios $r_{s}(z_d)/D_{V}(z)$ and the CMB acoustic scales $l_{A}$. It could give out the accelerating behaviors of the $Λ$CDM, $w$CDM and o$Λ$CDM models. As the direction of the degeneracy of $Ω_{m0}-w$ and $Ω_{m0}-Ω_{k0}$ are different for the CMB/BAO and BAO data, the CMB/BAO data show ability of breaking parameter degeneracy. Our tightest constraining results is from the BAO+Planck/BAO+$Ω_{b}h^2$+$Ω_{m}h^2$ data which…
The use of the baryonic acoustic oscillations (BAO) datasets offers a unique opportunity to connect the early universe and the late one. In this proceeding, we discuss recent results that used a marginalised likelihood to remove the $H_0-r_d $ degeneracy and then tested it on different dark energy (DE) models. It was found that this approach which does not rely on calibration on $r_d$ or $H_0$, allows us to obtain results, comparable to the ones calculated with standard likelihoods. Here we emphasize on the major differences that we observed for the two different BAO datasets that we employed …
A 2.5-3 sigma discrepancy has been reported between the baryonic acoustic oscillation peak (BAO) in the Lyman $α$ forest at $z\sim 2.34$ and the best fit Planck $Λ$CDM cosmology. To isolate the origin of the tension, we consider unanchored BAO, in which the standard BAO ruler is not calibrated, eliminating any dependence on cosmology before redshift $z\sim 2.34$. We consider BOSS BAO measurements at $z\sim 0.32$, 0.57 and 2.34, using the full 2-dimensional constraints on the angular and line of sight BAO scale, as well as isotropic BAO measurements by 6dF and SDSS at $z\sim 0.106$ and $z\sim 0…
Baryon acoustic oscillations (BAO) provide a robust standard ruler, and can be used to constrain the expansion history of the Universe at low redshift. Standard BAO analyses return a model-independent measurement of the expansion rate and the comoving angular diameter distance as function of redshift, normalized by the sound horizon at radiation drag. However, this methodology relies on anisotropic distance distortions of a fixed, pre-computed template (obtained in a given fiducial cosmology) in order to fit the observations. Therefore, it may be possible that extensions to the consensus $Λ$CD…
We conduct a selective analysis of the isotropic ($D_V$) and anisotropic ($AP$) components of the most recent Baryon Acoustic Oscillations (BAO) data. We find that these components provide significantly different constraints and could provide strong diagnostics for model selection, also in view of more precise data to arrive. For instance, in the $Λ$CDM model, we find a mild tension of $\sim 2 σ$ for the $Ω_m$ estimates obtained using $D_V$ and $AP$ separately. Considering both $Ω_k$ and $w$ as free parameters, we find that the concordance model is in tension with the best-fit values provided …
Revisiting the equation of state of dark energy from DESI BAO with SNe Ia and CMB
Institute for Gravitational Wave Astronomy, Henan Academy of Sciences（河南科学院引力波天文研究院）；School of Microelectronics, Qingdao University of Science and Technology（青岛科技大学微电子学院）
本文结合DESI BAO DR2、Pantheon+ SNe Ia与Planck 2018 CMB数据，采用红移截断策略分析w0waCDM模型，发现z~0.4-0.8数据会致约2σ偏差，无可靠证据支持其优于ΛCDM模型，偏差或源于统计波动与子样本局限。
We report the constraints of $H_0$ obtained from Wilkinson Microwave Anisotropy Probe (WMAP) combined with the latest baryonic acoustic oscillations (BAO) measurements. We use the BAO measurements from the 6dF Galaxy Survey (6dFGS), the SDSS DR7 main galaxies sample (MGS), the BOSS DR12 galaxies and the eBOSS DR14 quasars. Adding the recent BAO measurements to the cosmic microwave background (CMB) data from WMAP, we constrain cosmological parameters $Ω_m=0.298\pm0.005$, $H_0=68.36^{+0.53}_{-0.52}$ km s$^{-1}$ Mpc$^{-1}$, $σ_8=0.8170^{+0.0159}_{-0.0175}$ in a spatially flat $Λ$ cold dark matter…
One of the algorithms typically used for fitting anisotropic Baryon Acoustic Oscillations (BAO), $α_{\perp}D_{M, \text{fid}}(z)/r_{d, \text{fid}}=D_{M}(z)/r_{d}$, provides an excellent fit as $z\Rightarrow 0$. Yet, at $ z_{\text{drag}} \simeq 1060$, $D_{M, \text{fid}}(1060)/r_{d, \text{fid}}\simeq D_{M}(1060)/r_{d}$. Since $α_{\perp}$ does not change with increasing redshift, we conclude that the algorithms deviate from true solutions with increasing $z$. We investigate that departure through an assumption of a flat $Λ$CDM cosmology. At the relatively low redshifts at which isotropic BAO studi…
We investigate the non-linear evolution of Baryon Acoustic Oscillations (BAO) in the low-redshift matter power spectrum from the DEUS-FUR $Λ$CDM model simulation. This is the first cosmological N-body simulation encompassing the full observable cosmic volume, thus allowing cosmic variance limited predictions at BAO scales. We control the effect of numerical systematic errors using a series of large volume high-resolution simulations. The combined analysis allows us to measure the matter power spectrum between $z=0$ and $1$ to 1% over the entire BAO range, $0.03<k [\textrm{h Mpc}^{-1}]<0.3$, in…
We test the mutual consistency between the baryon acoustic oscillation measurements from the eBOSS SDSS final release, as well as the Pantheon supernova compilation in a model independent fashion using Gaussian process regression. We also test their joint consistency with the $Λ$CDM model, also in a model independent fashion. We also use Gaussian process regression to reconstruct the expansion history that is preferred by these two datasets. While this methodology finds no significant preference for model flexibility beyond $Λ$CDM, we are able to generate a number of reconstructed expansion hi…
We examine the impact of baryon acoustic oscillation (BAO) scale measurements on the discrepancy between the value of the Hubble constant ($H_0$) inferred from the local distance ladder and from Planck cosmic microwave background (CMB) data. While the BAO data alone cannot constrain $H_0$, we show that combining the latest BAO results with WMAP, Atacama Cosmology Telescope (ACT), or South Pole Telescope (SPT) CMB data produces values of $H_0$ that are $2.4-3.1σ$ lower than the distance ladder, independent of Planck, and that this downward pull was less apparent in some earlier analyses that us…
In this work, we explore the cosmological implications of different baryon acoustic oscillation (BAO) data, including the BAO data extracted by using the spherically averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and the BAO data obtained by using the anisotropic two-dimensional GC statistics (hereafter BAO2). To make a comparison, we also take into account the case without BAO data (hereafter NO BAO). Firstly, making use of these BAO data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we give the cosmological constraints of th…
The Baryon Acoustic Oscillations (BAO) provide a standard ruler for studying cosmic expansion. The recent observations of BAO in SDSS DR9 and DR11 take measurements of $H(z)$ at several different redshifts. It is argued that the behavior of dark energy could be constrained more effectively by adding high-redshift Hubble parameter data, such as the SDSS DR11 measurement of $H(z) = 222\pm7$ km/sec/Mpc at z = 2.34. In this paper, we investigate the significance of these BAO data in the flat $Λ$CDM model, by combining them with the recent observational data of the Hubble constant from local distan…
Probing dynamical dark energy with late-time data: Evidence, tensions, and the limits of the $w_0w_a$CDM framework
School of Physics and Astronomy, Sun Yat-Sen University（中山大学物理与天文学院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Plaksha University（普拉克斯哈大学）；College of Astronomy and Space Sciences, University of Chinese Academy of Sciences（中国科学院大学天文学与空间科学学院）；Graduate Program in Applied Physics, Federal University of Latin-American Integration（拉丁美洲联邦大学应用物理研究生项目）；Departamento de Engenharias e Ciências Exatas, Universidade Federal do Paraná（巴拉那联邦大学工程与自然科学系）；Department of Physics, Istanbul Technical University（伊斯坦布尔理工大学物理系）
本文通过结合CMB各向异性、DESI DR2、SDSS-IV、横向/角BAO（BAOtr）和Ia型超新星数据，测试$w_0w_a$CDM（CPL）框架与$Λ$CDM的差异，发现CPL推断依赖于数据集，CMB数据单独使用存在几何退化，而DESI DR2 BAO数据推动重建向弱现今加速发展，相比之下，CMB结合PP\&SH0ES和BAOtr更倾向于中等加速膨胀并显著减少哈勃矛盾。这种行为源于低红移距离信息：BAOtr和DESI/SDSS在$z\lesssim0.5$时偏好不同的BAO距离比，驱动了不同的CPL膨胀历史。通过比较角BAO尺度，包括共同的$z=0.510$点和保守的BAOtr局部插值（无外推），量化了这种不匹配。在CPL中，预重组物理固定，$r_{ m d}$几乎不变，因此$H_0$的变化被晚期膨胀自由度吸收而非声学 horizon的变化。贝叶斯证据同样依赖于低红移数据：当PP\&SH0ES和/或BAOtr包含时，它倾向于CPL，对于CMB单独或CMB+DESI是不确定的，而对于CMB+SDSS则略微倾向于$Λ$CDM。这些结果表明，CPL的明显支持及其缓解哈勃矛盾的能力并非普遍，这促使了更灵活的晚期模型和对BAO系统误差的更仔细审查。
Separately, neither electromagnetic (EM) observations nor gravitational wave (GW) observations can distinguish between the $f(T)$ model and the $Λ$CDM model effectively. To break this degeneration, we simulate the GW measurement based on the coming observation facilities, explicitly the Einstein Telescope. We make cross-validations between the simulated GW data and factual EM data, including the Pantheon, H(z), BAO and CMBR data, and the results show that they are consistent with each other. Anyway, the EM data itself have the $H_0$ tension problem which plays critical role in the distinguisha…
We propose a new consistency test for the $Λ$CDM cosmology using baryonic acoustic oscillations (BAO) and redshift space distortion (RSD) measurements from galaxy redshift surveys. Specifically, we determine the peak position of $fσ_8(z)$ in redshift $z$ offered by a RSD measurement, and compare it to the one predicted by the BAO observables assuming a flat $Λ$CDM cosmology. We demonstrate this new test using the simulated data for the DESI galaxy survey, and argue that this test complements those using the background observables alone, and is less subject to systematics in the RSD analysis, c…
Comparing measures of the Hubble and BAO tensions in $Λ$CDM and possible solutions in $f(Q)$ gravity
Institute of Cosmology & Gravitation, University of Portsmouth（朴茨茅斯大学宇宙学与引力研究所）；Scottish Universities Physics Alliance, University of Saint Andrews（圣安德鲁斯大学苏格兰大学物理联盟）
We model the nonlinear growth of cosmic structure in different dark energy models, using large volume N-body simulations. We consider a range of quintessence models which feature both rapidly and slowly varying dark energy equations of state, and compare the growth of structure to that in a universe with a cosmological constant. The adoption of a quintessence model changes the expansion history of the universe, the form of the linear theory power spectrum and can alter key observables, such as the horizon scale and the distance to last scattering. The difference in structure formation can be e…
We use the most recent type Ia supernovae (SNe Ia) observations to perform a statistical comparison between the standard $Λ$CDM model and its extensions [$w$CDM and $w(z)$CDM] and some alternative cosmologies: namely, the Dvali--Gabadadze--Porrati (DGP) model, a power-law $f(R)$ scenario in the metric formalism and an example of vacuum decay [$Λ(t)$CDM] cosmology in which the dilution of pressureless matter is attenuated with respect to the usual $a^{-3}$ scaling due to the interaction of the dark matter and dark energy fields. We perform a Bayesian model selection analysis using the \textsc{M…
Cosmography provides a model-independent way to map the expansion history of the Universe. In this paper we simulate a Euclid-like survey and explore cosmographic constraints from future Baryonic Acoustic Oscillations (BAO) observations. We derive general expressions for the BAO transverse and radial modes and discuss the optimal order of the cosmographic expansion that provide reliable cosmological constraints. Through constraints on the deceleration and jerk parameters, we show that future BAO data have the potential to provide a model-independent check of the cosmic acceleration as well as …
Standard analysis pipelines for measurements of Baryon Acoustic Oscillations (BAO) in galaxy surveys make use of a fiducial cosmological model to guide the data compression required to transform from observed redshifts and angles to the measured angular and radial BAO peak positions. In order to remove any dependence on the fiducial cosmology from the results, all models compared to the data should mimic the compression and its dependence on the fiducial model. In practice, approximations are made when testing models: (1) There is assumed to be no residual dependence on the fiducial cosmology …
We perform a Bayesian model selection analysis for different classes of phenomenological coupled scenarios of dark matter and dark energy with linear and non-linear interacting terms. We use a combination of some of the latest cosmological data such as type Ia supernovae (SNe Ia), cosmic chronometers (CC), cosmic microwave background (CMB) and two sets of baryon acoustic oscillations measurements, namely, 2-dimensional angular measurements (BAO2) and 3-dimensional angle-averaged measurements (BAO3). We find weak and moderate evidence against two-thirds of the interacting scenarios considered w…
Using current observations forecast type Ia supernovae (SNe Ia) Joint Lightcurve Analysis (JLA) and baryon acoustic oscillations (BAO), in this paper we investigate six bidimensional dark energy parameterisations in order to explore which has more constraining power. Our results indicate that for parameterisations that contain $z^2$-terms, the tension ($σ$-distance) between these datasets seems to be reduced and their behaviour are $<$1$σ$ compatible with $Λ$CDM. Also, the results obtained by performing their Bayesian evidence show a striking evidence in favour of the $Λ$CDM model, but only on…
We explore and compare the capabilities of the recent observations of standard cosmological probes and the future observations of gravitational-wave (GW) standard sirens on constraining cosmological parameters. It is carried out in the frameworks of two typical dynamical models of cosmology, i.e., the $ω_0ω_a$CDM model with $ω(z) = ω_0 +ω_a*z/(1+z)$, and the $ξ$-index model with $ρ_X\proptoρ_ma^ξ$, where $ω(z)$ is the dark energy equation of state, and $ρ_X$ and $ρ_m$ are the energy densities of dark energy and matter, respectively. In the cosmological analysis, the employed data sets include …
The Hubble tension and attempts to resolve it by modifying the physics of (or at) recombination motivate finding ways to determine $H_0$ and the sound horizon at the epoch of baryon decoupling $r_{\rm d}$ in ways that neither rely on a recombination model nor on late-time Hubble data. In this work, we investigate what one can learn from the current and future BAO data when treating $r_{\rm d}$ and $H_0$ as independent free parameters. It is well known that BAO gives exquisite constraints on the product $r_{\rm d}H_0$. We show here that imposing a moderate prior on $Ω_{\rm m} h^2$ breaks the de…
In this paper, linear first order expansion of deceleration parameter $q(z)=q_0+q_1(1-a)$ ($M_1$), constant jerk $j=j_0$ ($M_2$) and third order expansion of luminosity distance ($M_3$) are confronted with cosmic observations: SCP 307 SN Ia, BAO and observational Hubble data (OHD). Likelihood is implemented to find the best fit model parameters. All these models give the same prediction of the evolution of the universe which is undergoing accelerated expansion currently and experiences a transition from decelerated expansion to accelerated expansion. But, the transition redshift depends on the…
The Role of Big Bang Nucleosynthesis in Joint Cosmological Analyses
Boston University（波士顿大学）；University of California, Santa Barbara（加州大学圣塔芭芭拉分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；University of California, Berkeley（加州大学伯克利分校）
Two-point diagnostics $Om(z_i,z_j)$ and $Omh^2(z_i,z_j)$ have been introduced as an interesting tool for testing the validity of the $Λ$CDM model. Quite recently, Sahni, Shafieloo $\&$ Starobinsky (2014) combined two independent measurements of $H(z)$ from BAO data with the value of the Hubble constant $H_0$, and used the second of these diagnostics to test the $Λ$CDM model. Their result indicated a considerable tension between observations and predictions of the $Λ$CDM model. Since reliable data concerning expansion rates of the Universe at different redshifts $H(z)$ are crucial for the succe…
We use the emulation framework CosmoPower to construct and publicly release neural network emulators of cosmological observables, including the Cosmic Microwave Background (CMB) temperature and polarization power spectra, matter power spectrum, distance-redshift relation, baryon acoustic oscillation (BAO) and redshift-space distortion (RSD) observables, and derived parameters. We train our emulators on Einstein-Boltzmann calculations obtained with high-precision numerical convergence settings, for a wide range of cosmological models including $Λ$CDM, $w$CDM, $Λ$CDM+$N_\mathrm{eff}$, and $Λ$CDM…
We study observational constraints on the non-metricity $f(Q)$-gravity which reproduces an exact $Λ$CDM background expansion history while modifying the evolution of linear perturbations. To this purpose we use Cosmic Microwave Background (CMB) radiation, baryonic acoustic oscillations (BAO), redshift-space distortions (RSD), supernovae type Ia (SNIa), galaxy clustering (GC) and weak gravitational lensing (WL) measurements. We set stringent constraints on the parameter of the model controlling the modifications to the gravitational interaction at linear perturbation level. We find the model to…
Atlantic Technological University（大西洋科技大学）；School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所物理学院）；Department of Physics, Shanghai University（上海大学物理系）
In a previous communication we showed that a joint analysis of Cosmic Microwave Background (CMB) data and the current measurement of the local expansion rate favours a model with a scale invariant spectrum (HZ) over the minimal $Λ$CDM scenario provided that the effective number of relativistic degrees of freedom, $N_{eff}$, is taken as a free parameter. Such a result is basically obtained due to the Hubble Space Telescope (HST) value of the Hubble constant, $H_0 = 73.24 \pm 1.74$ $\rm{km.s^{-1}.Mpc^{-1}}$ (68\% C.L.), as the CMB data alone discard the HZ+$N_{eff}$ model. Although such a model …
An important problem in precision cosmology is the determination of the effects of averaging and backreaction on observational predictions, particularly in view of the wealth of new observational data and improved statistical techniques. In this paper, we discuss the observational viability of a class of averaged cosmologies which consist of a simple parametrized phenomenological two-scale backreaction model with decoupled spatial curvature parameters. We perform a Bayesian model selection analysis and find that this class of averaged phenomenological cosmological models is favored with respec…
