We propose a new intuitive metric for evaluating the tension between two experiments, and apply it to several data sets. While our metric is non-optimal, if evidence of tension is detected, this evidence is robust and easy to interpret. Assuming a flat $Λ$CDM cosmological model, we find that there is a modest $2.2σ$ tension between the DES Year 1 results and the ${\it Planck}$ measurements of the Cosmic Microwave Background (CMB). This tension is driven by the difference between the amount of structure observed in the late-time Universe and that predicted from fitting the ${\it Planck}$ data, and appears to be unrelated to the tension between ${\it Planck}$ and local esitmates of the Hubble rate. In particular, combining DES, Baryon Acoustic Oscillations (BAO), Big-Bang Nucleosynthesis (BBN), and supernovae (SNe) measurements recovers a Hubble constant and sound horizon consistent with ${\it Planck}$, and in tension with local distance-ladder measurements. If the tension between these various data sets persists, it is likely that reconciling ${\it all}$ current data will require breaking the flat $Λ$CDM model in at least two different ways: one involving new physics in the early Universe, and one involving new late-time Universe physics.
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…
Recently Risaliti \& Lusso [Nature Astron. 3 (2019) 3 272] reported new measurements of the expansion rate of the Universe by constructing the Hubble diagram of 1598 quasars in the redshift range $0.5<z<5.5$. It is claimed a $4σ$ tension with the standard concordance $Λ$CDM concerning both the fractionary matter density $Ω_{m0}$ and the dark energy equation of state parameter $w_{de}$ standard values. In this work we promote an independent analysis of the same data set using a model-independent estimator for cosmic acceleration. Our results corroborate that the source of such tension can be re…
Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between datasets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and us…
A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift <z> = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 <= z <= 1.8 of our current investigation. Its location on the sky is ~ 8.8 deg north (~ 615 Mpc projected) of the Clowes & Campusano LQG at the same redshift, <z>…
Since the number of dark energy models have rapidly increased over the last years, some model-independent methods have been developed in order to analyse the cosmological evolution in a phenomenological way. In this manuscript, we analyse some of these approaches and their shortcomings to provide reliable information.
We show how future gravitational-wave detectors would be able of discriminating between the concordance LCDM cosmological model and up-to-date competing alternatives, e.g. dynamical dark energy models (DE) or modified gravity theories (MG). Our method consists in using the weak-lensing magnification effect that affects a standard-siren signal because of its travelling trough the Universe's large-scale structure. As a demonstration, we present constraints on DE and MG from proposed gravitational-wave detectors, namely ET and DECIGO/BBO.
I briefly outline a new physical interpretation to the average cosmological parameters for an inhomogeneous universe with backreaction. The variance in local geometry and gravitational energy between ideal isotropic observers in bound structures and isotropic observers at the volume average location in voids plays a crucial role. Fits of a model universe to observational data suggest the possibility of a new concordance cosmology, in which dark energy is revealed as a mis-identification of gravitational energy gradients that become important when voids grow at late epochs.
The success of present and future cosmological studies is tied to the ability to detect discrepancies in complex data sets within the framework of a cosmological model. Tensions caused by the presence of unknown systematic effects need to be isolated and corrected to increase the overall accuracy of parameter constraints, while discrepancies due to new physical phenomena need to be promptly identified. We develop a full set of estimators of internal and mutual agreement and disagreement, whose strengths complement each other. These allow to take into account the effect of prior information and…
We show how higher derivatives of the expansion factor can be developed into a null diagnostic for concordance cosmology (LCDM). It is well known that the Statefinder -- the third derivative of the expansion factor written in dimensionless form, a^{(3)}/aH^3, equals unity for LCDM. We generalize this result to higher derivatives of the expansion factor and demonstrate that the hierarchy, a^{(n)}/aH^n, can be converted to a form that stays pegged at unity in concordance cosmology. This remarkable property of the Statefinder hierarchy enables it to be used as an extended null diagnostic for the …
It has been claimed recently that massive sterile neutrinos could bring about a new concordance between observations of the cosmic microwave background (CMB), the large-scale structure (LSS) of the Universe, and local measurements of the Hubble constant, $H_0$. We demonstrate that this apparent concordance results from combining datasets which are in significant tension, even within this extended model, possibly indicating remaining systematic biases in the measurements. We further show that this tension remains when the cosmological model is further extended to include significant tensor mode…
According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological $N$-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This…
There exist power contrast in even and odd multipoles of WMAP power spectrum at low and intermediate multipole range. This anomaly is explicitly associated with the angular power spectrum, which are heavily used for cosmological model fitting. Having noted this, we have investigated whether even(odd) multipole data set is consistent with the WMAP concordance model. Our investigation shows WMAP concordance model does not make a good fit for even(odd) multipole data set, and there exist tension between two data subsets. Noting tension is highest in primordial power spectrum parameters, we have a…
Yes. In a perturbed Friedmann model, the difference of the Hubble constants measured in two rest-frames is independent of the source peculiar velocity and depends only on the relative velocity of the observers, to lowest order in velocity. Therefore this difference should be zero when averaging over sufficient sources, which are at large enough distances to suppress local nonlinear inhomogeneity. We use a linear perturbative analysis to predict the Doppler effects on redshifts and distances. Since the observed redshifts encode the effect of local bulk flow due to nonlinear structure, our linea…
The generalized Chaplygin gas cosmology provides a prime example for the class of unified dark matter models, which substitute the two dark components of the standard cosmological LCDM concordance model by a single dark component. The equation of state of the generalized Chaplygin gas is characterised by a parameter alpha such that the standard LCDM model is recovered in the case alpha=0 with respect to the background dynamics and the cosmic microwave background (CMB) statistics. This allows to investigate the concordance of different cosmological data sets with respect to alpha. We compare th…
We are at an interesting juncture in cosmology. With new methods and technology, the accuracy in measurement of the Hubble constant has vastly improved, but a recent tension has arisen that is either signaling new physics or as-yet unrecognized uncertainties.
We test the consistency between Planck temperature and polarization power spectra and the concordance model of $Λ$ Cold Dark Matter cosmology ($Λ$CDM) within the framework of Crossing statistics. We find that Planck TT best fit $Λ$CDM power spectrum is completely consistent with EE power spectrum data while EE best fit $Λ$CDM power spectrum is not consistent with TT data. However, this does not point to any systematic or model-data discrepancy since in the Planck EE data, uncertainties are much larger compared to the TT data. We also investigate the possibility of any deviation from $Λ$CDM mod…
Smoothing over structures in general relativity leads to a renormalisation of the background, and potentially many other effects which are poorly understood. Observables such as the distance-redshift relation when averaged on the sky do not necessarily yield the same smooth model which arises when performing spatial averages. These issues are thought to be of technical interest only in the standard model of cosmology, giving only tiny corrections. However, when we try to calculate observable quantities such as the all-sky average of the distance-redshift relation, we find that perturbation the…
El Gordo (ACT-CL J0102-4915) is an extremely massive galaxy cluster ($M_{200} \approx 3 \times 10^{15}$ $M_{\odot}$) at redshift $z = 0.87 $ composed of two subclusters with mass ratio 3.6 merging at speed $V_{infall} \approx 2500$ km/s. Such a fast collision between individually rare massive clusters is unexpected in Lambda cold dark matter ($Λ$CDM) cosmology at such high $z$. However, this is required for non-cosmological hydrodynamical simulations of the merger to match its observed properties (Zhang et al. 2015). Here, we determine the probability of finding a similar object in a $Λ$CDM co…
The tension among inferences of Hubble constant ($H_0$) is found in a large array of datasets combinations. Modification to the late expansion history is the most direct solution to this discrepancy. In this work, we examine the viability of restoring the cosmological concordance with a novel version of transitional dark energy (TDE). The main anchors for the cosmic distance scale: cosmic microwave background (CMB) radiation, baryon acoustic oscillation (BAO), and Type Ia supernova (SNe Ia) calibrated by Cepheids form a "impossible trinity", i.e., it's plausible to reconcile with any two of th…
Cosmological Concordance in an Especially Opaque Universe: A Tentative Cosmological Detection of Physical Neutrino Mass in $Λ$CDM
Center for Theoretical Physics – a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院莱因韦伯理论物理中心）；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）
We study the global agreement between the most recent observations of the Cosmic Microwave Background temperature and polarization anisotropies angular power spectra released by the Atacama Cosmology Telescope and the Planck satellite in various cosmological models that differ by the inclusion of different combinations of additional parameters. By using the Suspiciousness statistic, we show that the global "CMB tension" between the two experiments, quantified at the Gaussian equivalent level of $\sim 2.5\,σ$ within the baseline $Λ$CDM, is reduced at the level of $1.8σ$ when the effective numbe…
A constant-rate creation of dark particles in the late-time FLRW spacetime provides a cosmological model in accordance with precise observational tests. The matter creation backreaction implies in this context a vacuum energy density scaling linearly with the Hubble parameter, which is consistent with the vacuum expectation value of the QCD condensate in a low-energy expanding spacetime. Both the cosmological constant and coincidence problems are alleviated in this scenario. We discuss the cosmological model that arises in this context and present a joint analysis of observations of the first …
We perform null tests of the concordance model, using $H(z)$ measurements that mimic next-generation surveys such as Euclid and the SKA. To this end, we deploy a non-parametric method, so that we make minimal assumptions about the fiducial cosmology as well as the statistical analysis. We produce simulations assuming different cosmological models in order to verify how well we can distinguish between their signatures. We find that SKA- and Euclid-like surveys should be able to discriminate sharply between the concordance and alternative dark energy models that are compatible with the Planck CM…
The Fractal Bubble model has been proposed as a viable cosmology that does not require dark energy to account for cosmic acceleration, but rather attributes its observational signature to the formation of structure. In this paper it is demonstrated that, in contrast to previous findings, this model is not a good fit to cosmological supernovae data; there is significant tension in the best fit parameters obtained from different samples, whereas LCDM is able to fit all datasets consistently. Furthermore, the concordance between galaxy clustering scales and data from the cosmic microwave backgrou…
In this work, we study the cosmological constant problem and Hubble tension in the void-dominated cosmology scenario \cite{Yusofi:2022hgg}. For this goal, we will first consider the cosmic voids in the cosmic web as interconnected ideal spherical bubbles at the early Planck scale and late large scale. By heuristic calculations for each cosmic void, we obtain particular mass density and cosmological constant that are the same order of magnitude as the entire universe on any scale. The values obtained for the cosmological constant vary from scale to scale. As a result, it will be shown that ther…
Addressing the discrepancy between the late and early time measurements of the Hubble parameter, $H_0$, and the so-called $S_8$ parameter has been a challenge in precision cosmology. Several models are present to address these tensions, but very few of them can do so simultaneously. In the past, we have suggested Banks-Zaks/Unparticles as an emergent Dark Energy model and claimed that it can ameliorate the Hubble tension. In this work, we test this claim and perform a likelihood analysis of the model and its parameters are given current data and compare it to $Λ$CDM. The model offers a possibl…
The apparent accelerating expansion of the Universe is forcing us to examine the foundational aspects of the standard model of cosmology -- in particular, the fact that dark energy is a direct consequence of the homogeneity assumption. We discuss the foundations of the assumption of spatial homogeneity, in the case when the Copernican Principle is adopted. We present results that show how (almost-) homogeneity follows from (almost-) isotropy of various observables. The analysis requires the fully nonlinear field equations -- i.e., it is not possible to use second- or higher-order perturbation …
Assuming a spatially flat universe, we study the cosmological viability of an infrared corrected teleparallel gravity model, which accounts for late acceleration by weakening gravity at later times on cosmological distances. The theory does not introduce any additional free parameters into the cosmological model, as is commonly the case with modified gravity based cosmologies. This feature renders the cosmological model statistically comparable, on equal footing, with $Λ$CDM. In this context, using recent cosmological observations -- Pantheon supernova Type Ia, Hubble constant $H_0$, Baryon ac…
We use a complete and rigorous statistical indicator to measure the level of concordance between cosmological data sets, without relying on the inspection of the marginal posterior distribution of some selected parameters. We apply this test to state of the art cosmological data sets, to assess their agreement within the $Λ$CDM model. We find that there is a good level of concordance between all the experiments with one noticeable exception. There is substantial evidence of tension between the CMB, temperature and polarization, measurements of the Planck satellite and the data from the CFHTLen…
(abridged) Predictions of the Concordance Cosmological Model (CCM) of the structures in the environment of large spiral galaxies are compared with observed properties of Local Group galaxies. Five new most probably irreconcilable problems are uncovered. However, the Local Group properties provide hints that may lead to a solution of the above problems The DoS and bulge--satellite correlation suggest that dissipational events forming bulges are related to the processes forming phase-space correlated satellite populations. Such events are well known to occur since in galaxy encounters energy and…
Direct observations of the Hubble rate, from cosmic chronometers and the radial baryon acoustic oscillation scale, can out-perform supernovae observations in understanding the expansion history, because supernovae observations need to be differentiated to extract H(z). We use existing H(z) data and smooth the data using a new Gaussian Processes package, GaPP, from which we can also estimate derivatives. The obtained Hubble rate and its derivatives are used to reconstruct the equation of state of dark energy and to perform consistency tests of the LCDM model, some of which are newly devised her…
The determination of the Hubble constant has been a central goal in observational astrophysics for nearly 100 years. Extraordinary progress has occurred in recent years on two fronts: the cosmic distance ladder measurements at low redshift and cosmic microwave background (CMB) measurements at high redshift. The CMB is used to predict the current expansion rate through a best-fit cosmological model. Complementary progress has been made with baryon acoustic oscillation (BAO) measurements at relatively low redshifts. While BAO data do not independently determine a Hubble constant, they are import…
Since the public release of Planck data, several attempts have been made to explain the observed small tensions with other data-sets, most of them involving an extension of the ΛCDM Model. We try here an alternative approach to the data analysis, based on separating the constraints coming from the different epochs in cosmology, in order to assess which part of the Standard Model generates the tension with the data. To this end, we perform a particular analysis of Planck data probing only the early cosmological evolution, until the time of photon decoupling. Then, we utilise this result to see …
The overall cosmological parameter tension between the Atacama Cosmology Telescope 2020 (ACT) and Planck 2018 data within the concordance cosmological model is quantified using the suspiciousness statistic to be 2.6$σ$. Between ACT and the South Pole Telescope (SPT) we find a tension of 2.4$σ$, and 2.8$σ$ between ACT and Planck+SPT combined. While it is unclear whether the tension is caused by statistical fluctuations, systematic effects or new physics, caution should be exercised in combining these cosmic microwave background datasets in the context of the $Λ$CDM standard model of the univers…
Current tensions in cosmology, including $H_0$ and $σ_8$, provide one of the strong reasons to suspect the existence of physics beyond the standard model of cosmology ($Λ$CDM). In this paper, we investigate if there is a relation between these tensions and beyond cold dark matter scenarios. To model non-CDM, we assume a decaying dark matter (DDM) which is unstable and may decay into two daughter particles, a combination of cold dark matter, warm dark matter, and dark radiation, to explore a vast era of possibilities. We checked our model against CMB data and could show that decaying dark matte…
Cosmological tensions in the era of precision cosmology: Insights from Tensions in Cosmology 2025
University of Sheffield（谢菲尔德大学）；University of Malta（马耳他大学）；National Observatory of Athens（雅典国家天文台）；University of Science and Technology of China（中国科学技术大学）；Universidad Católica del Norte（天主教主教大学）
With the increasing precision of recent cosmological surveys and the discovery of important tensions within the $Λ$CDM paradigm, it is becoming more and more important to develop tools to quantify accurately the discordance between different probes. One such tool is the Surprise statistic, a measure based on the Kullback-Leibler divergence. The Surprise, however, has been up to now applied only under its Gaussian approximation, which can fail to properly capture discordance in cases that deviate significantly from Gaussianity. In this paper we developed the \texttt{klsurprise} code which compu…
We perform a comprehensive analysis of the most common early- and late-Universe solutions to the $H_0$, Ly-$α$, and $S_8$ discrepancies. When considered on their own, massive neutrinos provide a natural solution to the $S_8$ discrepancy at the expense of increasing the $H_0$ tension. If all extensions are considered simultaneously, the best-fit solution has a neutrino mass sum of $\sim 0.4$ eV, a dark energy equation of state close to that of a cosmological constant, and no additional relativistic degrees of freedom. However, the $H_0$ tension, while weakened, remains unresolved. Motivated by …
Current cosmological constraints on the scalar spectral index of primordial fluctuations $n_{\rm s}$ in the $Λ$CDM model have excluded the minimal scale-invariant Harrison-Zel'dovich model ($n_{\rm s}=1$; hereafter HZ) at high significance, providing support for inflation. In recent years, however, some tensions have emerged between different cosmological datasets that, if not due to systematics, could indicate the presence of new physics beyond the $Λ$CDM model. In the light of these developments, we evaluate the Bayesian evidence against HZ in different data combinations and model extensions…
We develop a new phenomenological model that addresses current tensions between observations of the early and late Universe. Our scenario features: (i) a decaying dark energy fluid (DDE), which undergoes a transition at $z \sim 5,000$, to raise today's value of the Hubble parameter -- addressing the $H_0$ tension, and (ii) an ultra-light axion (ULA), which starts oscillating at $z\gtrsim 10^4$, to suppress the matter power spectrum -- addressing the $S_8$ tension. Our Markov Chain Monte Carlo analyses show that such a Dark Sector model fits a combination of Cosmic Microwave Background (CMB), B…
The recent local measurement of Hubble constant leads to a more than $3σ$ tension with Planck + $Λ$CDM (Riess {\it et al} 2018). In this article we study the $H_0$ tension in non-flat QCDM cosmology, where Q stands for a minimally coupled and slowly-or-moderately rolling quintessence field $ϕ$ with a smooth potential $V(ϕ)$. By generalizing the QCDM one-parameter and three-parameter parametrizations in Huang {\it et al} 2011 to non-flat universe and using the latest cosmological data, we find that the $H_0$ tension remains above $3.2σ$ level for this class of model.
The concordance of the $Λ$CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter $Ω_K<0$. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datas…
Hubble tension in k-essence: Evidence for robust tension alleviation
Botswana International University of Science and Technology（博茨瓦纳国际科学与技术大学）；University of Cape Town（开普敦大学）；North-West University（西北大学）；Omdurman Islamic University（恩图曼伊斯兰大学）
We combine model-independent reconstructions of the expansion history from the latest Pantheon supernovae distance modulus compilation and measurements from baryon acoustic oscillation to test some important aspects of the concordance model of cosmology namely the FLRW metric and flatness of spatial curvature. We then use the reconstructed expansion histories to fit growth measurement from redshift-space distortion and obtain strong constraints on $(Ω_\mathrm{m},γ,σ_8)$ in a model independent manner. Our results show consistency with a spatially flat FLRW Universe with general relativity to go…
We study the fit of cosmological models with two additional free parameters $N_\mathrm{eff}$ and $ξ_e$ in addition to the parameters of $Λ$CDM. We introduce extra radiation components such as hot axions or sterile neutrinos in addition to the energy density of neutrinos with large neutrino degeneracy. Then, a larger $N_\mathrm{eff}$ is allowed without spoiling Big Bang Nucleosynthesis (BBN), as positive neutrino degeneracy $ξ_e$ could improve BBN fit. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae (SNeIa), it can be seen that the Hubble tension…
This article looks at how inhomogeneous spacetime models may be significant for cosmology. First it looks at how the averaging process may affect large scale dynamics, with backreaction effects leading to effective contributions to the averaged energy-momentum tensor. Secondly it considers how local inhomogeneities may affect cosmological observations in cosmology, possibly significantly affecting the concordance model parameters. Thirdly it presents the possibility that the universe is spatially inhomogeneous on Hubble scales, with a violation of the Copernican principle leading to an apparen…
