Recent analyses combining DESI baryon acoustic oscillation (BAO) measurements with other cosmological observations have reported indications of departures from the $Λ$CDM model within dynamical dark energy scenarios. We investigate whether such deviations are reproduced consistently in $f(T)$ gravity and whether they persist when different cosmological observations are combined. Using the DESI DR2 BAO measurements, Cosmic Microwave Background (CMB), and Pantheon+ Type Ia Supernovae (SNe Ia) sample, we constrain three representative $f(T)$ models: the power-law, exponential, and hyperbolic-tangent models. We compare the constraints obtained from different combinations of data, distinguishing changes in marginalized parameter distributions from changes in the relative statistical performance of the models. For the power-law model, the mild deviation from the $Λ$CDM model obtained from BAO+CMB disappears after the SNe Ia data are included. In contrast, the exponential model retains a preference for a nonzero deformation parameter in the full analysis, while the allowed parameter space of the hyperbolic-tangent model changes substantially after the CMB distance priors are included. Importantly, the parameter-level deviation found for the exponential model does not lead to a clear statistical preference over the $Λ$CDM model according to the information criteria, whereas the hyperbolic-tangent model shows a poorer statistical performance for the combined data. Despite these differences in the model constraints, the inferred transition redshift $z_T$ remains relatively stable among the three models and data combinations. Our results show that the departures from the $Λ$CDM model indicated by DESI analyses are not a generic feature of $f(T)$ gravity, but depend strongly on the specific modified gravity parameterization and on the combination of cosmological observations.
Probing departures from $Λ$CDM by late-time datasets
Babeș-Bolyai University（博巴伊-波约大学）；Khazar University（哈萨尔大学）；Indian Institute of Astrophysics（印度天体物理研究所）；Università di Napoli “Federico II”（那不勒斯费德里科二世大学）；Istituto Nazionale di Fisica Nucleare (INFN), sez. di Napoli（意大利国家核物理研究所那不勒斯分部）；Scuola Superiore Meridionale（南方高等学院）；Zhejiang Normal University（浙江师范大学）
The morphological properties of large scale structure of the Universe can be fully described by four Minkowski functionals (MFs), which provide important complementary information to other statistical observables such as the widely used 2-point statistics in configuration and Fourier spaces. In this work, for the first time, we present the differences in the morphology of large scale structure caused by modifications to general relativity (to address the cosmic acceleration problem), by measuring the MFs from N-body simulations of modified gravity and general relativity. We find strong statist…
As modern precision cosmological measurements continue to show agreement with the broad features of the standard $Λ$-Cold Dark Matter ($Λ$CDM) cosmological model, we are increasingly motivated to look for small departures from the standard model's predictions which might not be detected with standard approaches. While searches for extensions and modifications of $Λ$CDM have to date turned up no convincing evidence of beyond-the-standard-model cosmology, the list of models compared against $Λ$CDM is by no means complete and is often governed by readily-coded modifications to standard Boltzmann …
We investigate the interacting dark energy models by using the diagnostics of statefinder hierarchy and growth rate of structure. We wish to explore the deviations from $Λ$CDM and to differentiate possible degeneracies in the interacting dark energy models with the geometrical and structure growth diagnostics. We consider two interacting forms for the models, i.e., $Q_1=βHρ_c$ and $Q_2=βHρ_{de}$, with $β$ being the dimensionless coupling parameter. Our focus is the I$Λ$CDM model that is a one-parameter extension to $Λ$CDM by considering a direct coupling between the vacuum energy ($Λ$) and col…
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 cosmological constraints on K-mouflage models of modified gravity. We consider two scenarios: one where the background evolution is free to deviate from $Λ$CDM (K-mouflage) and another one which reproduces a $Λ$CDM expansion (K-mimic), implementing both of them into the EFTCAMB code. We discuss the main observational signatures of these models and we compare their cosmological predictions to different datasets, including CMB, CMB lensing, SNIa and different galaxy catalogues. We argue about the possibility of relieving the $H_0$ and weak lensing tensions within these models, fin…
Kinematical models are constrained by the latest observational data from geometry-distance measurements, which include 557 type Ia supernovae (SNIa) Union2 data and 15 observational Hubble data. Considering two parameterized deceleration parameter, the values of current deceleration parameter $q_{0}$, jerk parameter $j_{0}$ and transition redshift $z_{T}$, are obtained. Furthermore, we show the departures for two parameterized kinematical models from $Λ$CDM model according to the evolutions of jerk parameter $j(z)$. Also, it is shown that the constraint on jerk parameter $j(z)$ is weak by the …
Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-$Λ$CDM Interpretations, and Tensions
College of Sciences, Northeastern University（东北大学理学院）；School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS（杭州高等研究院基础物理与数学科学学院，UCAS）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；MOE Key Laboratory of Data Analytics and Optimization for Smart Industry, Northeastern University（东北大学智能工业数据优化与分析教育部重点实验室）；National Frontiers Science Center for Industrial Intelligence and Systems Optimization, Northeastern University（东北大学工业智能与系统优化前沿科学中心）
Recent measurements of the parameters of the Concordance Cosmology Model ($Λ$CDM) done in the low-redshift Universe with Supernovae Ia/Cepheids, and in the distant Universe done with Cosmic Microwave Background (CMB) imply different values for the Hubble constant (67.4 $\pm$ 0.5 km s$^{-1}$ Mpc$^{-1}$ from Planck vs 74.03 $\pm$ 1.42 km s$^{-1}$ Mpc$^{-1}$, Riess et al. 2019). This Hubble constant tension implies that either the systematic errors are underestimated, or the $Λ$CDM does not represent well the observed expansion of the Universe. Since quasars - active galactic nuclei - can be obse…
The cosmological principle states that the Universe is statistically homogeneous and isotropic at large distance scales. There currently exist many observations which indicate a departure from this principle. It has been shown that many of these observations can be explained by invoking superhorizon cosmological perturbations and may be consistent with the Big Bang paradigm. Remarkably, these modes simultaneously explain the observed Hubble tension, i.e., the discrepancy between the direct and indirect measurements of the Hubble parameter. We propose several tests of the cosmological principle…
In this paper, we have studied the dynamical aspects of some cosmological models in an isotropic space-time within the framework of an extended gravity theory. Two accelerating cosmological models are presented with quasi-de Sitter (QDS) and linear combination of exponential (LCE) scale factors. The geometrical testing mechanism has been performed and analysed. While the results of the QDS model show a departure from the concordant $Λ$CDM model, the resulting behavior of the LCE model seems to be compatible with the $Λ$CDM model only at the present epoch and is incompatible in the near past.
Recent analyses \cite{Nesseris:2017vor,Kazantzidis:2018rnb} have indicated that an effective Newton's constant $G_{\rm eff}(z)$ decreasing with redshift may relieve the observed tension between the Planck15 best fit $Λ$CDM cosmological background ({\it i.e.} Planck15/$Λ$CDM) and the corresponding $Λ$CDM background favored by growth $fσ_8$ and weak lensing data. We investigate the consistency of such a decreasing $G_{\rm eff}(z)$ with some viable scalar-tensor models and $f(R)$ theories. We stress that $f(R)$ theories generically can not lead to a decreasing $G_{\rm eff}(z)$ for any cosmologica…
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 baseline with current cosmological observations to forecast the power of the Dark Energy Spectroscopic Instrument (DESI) in two ways: 1. the gain in constraining power of parameter combinations in the standard $Λ$CDM model, and 2. the reconstruction of quintessence models of dark energy. For the former task we use a recently developed formalism to extract the leading parameter combinations constrained by different combinations of cosmological survey data. For the latter, we perform a non-parametric reconstruction of quintessence using the Effective Field Theory of Dark Energy. Using mock DE…
$w_0w_a$ or $bc$: DESI constraints on relative baryon-CDM perturbations
Center for Theoretical Physics – a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院理论物理中心（莱因韦伯研究所））；The NSF AI Institute for Artificial Intelligence and Fundamental Interactions（美国国家科学基金会人工智能基础相互作用研究所）；Department of Physics, Columbia University（哥伦比亚大学物理系）；NASA Hubble Fellowship Program（美国国家航空航天局哈勃奖学金项目）；Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève（日内瓦大学理论物理系与天体粒子物理中心）；Leinweber Institute for Theoretical Physics at Stanford（斯坦福大学莱因韦伯理论物理研究所）；Kavli Institute for Particle Astrophysics and Cosmology（卡弗里粒子天体物理学与宇宙学研究所）
The cosmological parameters prefered by the cosmic microwave background (CMB) primary anisotropies predict many more galaxy clusters than those that have been detected via the thermal Sunyaev-Zeldovich (tSZ) effect. This tension has attracted considerable attention since it could be evidence of physics beyond the simplest $Λ$CDM model. However, an accurate and robust calibration of the mass-observable relation for clusters is necessary for the comparison, which has been proven difficult to obtain so far. Here, we present new contraints on the mass-pressure relation by combining tSZ and CMB len…
We confront the concordance (standard) model of cosmology, the spatially flat $Λ$CDM Universe with power-law form of the primordial spectrum with Planck CMB angular power spectrum data searching for possible smooth deviations beyond the flexibility of the standard model. The departure from the concordance cosmology is modeled in the context of Crossing statistic and statistical significance of this deviation is used as a measure to test the consistency of the standard model to the Planck data. Derived Crossing functions suggest the presence of some broad features in angular spectrum beyond the…
Under the assumption of a flat Lambda-CDM cosmology, recent data from the Planck satellite point toward a Hubble constant that is in tension with that measured by gravitational lens time delays and by the local distance ladder. Prosaically, this difference could arise from unknown systematic uncertainties in some of the measurements. More interestingly -- if systematics were ruled out -- resolving the tension would require a departure from the flat Lambda-CDM cosmology, introducing for example a modest amount of spatial curvature, or a non-trivial dark energy equation of state. To begin to add…
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…
Inference of matter power spectrum at z=0 using DESI DR1 Full-Shape data
University of Sussex（萨塞克斯大学）；University of Queensland（昆士兰大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Boston University（波士顿大学）；Università degli Studi di Milano（米兰大学）；INAF-Osservatorio Astronomico di Brera（INAF-布雷拉天文台）；University College London（伦敦大学学院）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究研究所）；Institute of Space Sciences, ICE-CSIC（空间科学研究所，ICE-CSIC）
We investigated the evolution of the background expansion and the growth rate of the matter density fluctuations in the scalar field $ϕ$CDM Ratra-Peebles model. We constrained the model parameter $α$ and the matter density parameter $Ω_{\rm m}$ using the recent measurements of the growth rate of the matter density fluctuations and baryon acoustic oscillation peak position. In addition, we studied a number of the $ϕ$CDM scalar field models in order to determine whether or not it would be possible to discriminate them from the $Λ$CDM model using predicted data for the future Dark Energy Spectros…
The Cosmic Rush Hour: Rapid Formation of Bright, Massive, Disky, Star-Forming Galaxies as Signatures of Early-Universe Physics
Massachusetts Institute of Technology（麻省理工学院）；Center for Astrophysics | Harvard & Smithsonian（天体物理中心 | 哈佛与史密森尼学会）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of Cambridge（剑桥大学）
Recently, in [1], we presented the first combined non-parametric reconstruction of the three time-dependent functions that capture departures from the standard cosmological model, $Λ$CDM, in the expansion history and gravitational effects on matter and light from the currently available combination of the background and large scale structure data. The reconstruction was performed with and without a theory-informed prior, built on the general Horndeski class of scalar-tensor theories, that correlates the three functions. In this work, we perform a decomposition of the prior and posterior covari…
We study observational constraints on a specific dark energy model in the framework of Gleyzes-Langlois-Piazza-Vernizzi theories, which extends the Galileon ghost condensate (GGC) to the domain of beyond Horndeski theories. In this model, we show that the Planck cosmic microwave background (CMB) data, combined with datasets of baryon acoustic oscillations, supernovae type Ia, and redshift-space distortions, give the tight upper bound $|α_{\rm H}^{(0)}| \le {\cal O}(10^{-6})$ on today's beyond-Horndeski (BH) parameter $α_{\rm H}$. This is mostly attributed to the shift of CMB acoustic peaks ind…
This work determines the degree to which a standard Lambda-CDM analysis based on type Ia supernovae can identify deviations from a cosmological constant in the form of a redshift-dependent dark energy equation of state w(z). We introduce and apply a novel random curve generator to simulate instances of w(z) from constraint families with increasing distinction from a cosmological constant. After producing a series of mock catalogs of binned type Ia supernovae corresponding to each w(z) curve, we perform a standard Lambda-CDM analysis to estimate the corresponding posterior densities of the abso…
Interacting dark energy after DESI DR2: a challenge for $Λ$CDM paradigm?
Presidency University（总统大学）；Durban University of Technology（德班理工大学）；National Observatory of Athens（雅典国家天文台）；Universidad Católica del Norte（北天主教大学）；University of Science and Technology of China（中国科学技术大学）；Liaoning Normal University（辽宁师范大学）
New corrections to General Relativity are considered in the context of modified $f(R)$ gravity, that satisfy cosmological and local gravity constraints. The proposed models behave asymptotically as $R-2Λ$ at large curvature and show the vanishing of the cosmological constant at the flat spacetime limit. The chameleon mechanism and thin shell restrictions for local systems were analyzed, and bounds on the models were found. The steepness of the deviation parameter $m$ at late times leads to measurable signal of scalar-tensor regime in matter perturbations, that allows to detect departures form …
Recent studies by Solà Peracaula, Gómez-Valent, de Cruz Pérez and Moreno-Pulido (2019,2020) have pointed out the intriguing possibility that Brans-Dicke cosmology with constant vacuum energy density (BD-$Λ$CDM) may be able to alleviate the $H_0$ and $σ_8$ tensions that are found in the framework of the concordance cosmological model (GR-$Λ$CDM). The fitting analyses presented in these works indicate a preference for values of the effective gravitational coupling appearing in the Friedmann equation, $G$, about $4-9\%$ larger than Newton's constant (as measured on Earth), and mildy evolving with…
