We present a detailed investigation of the Rastall gravity extension of the standard $Λ$CDM model. We review the model for two simultaneous modifications of different nature in the Friedmann equation due to the Rastall gravity: the new contributions of the material (actual) sources (considered as effective source) and the altered evolution of the material sources. We discuss the role/behavior of these modifications with regard to some low redshift tensions, including the so-called $H_0$ tension, prevailing within the standard $Λ$CDM. We constrain the model at the level of linear perturbations, and obtain the first constraints through a robust and accurate analysis using the latest full Planck CMB data, with and without including BAO data. We find that the Rastall parameter $ε$ (null for general relativity) is consistent with zero at 68\% CL (with a tendency towards positive values, $-0.0001 < ε< 0.0007$ (CMB+BAO) at 68\% CL), which in turn implies no significant statistical evidence for deviation from general relativity, and also a precision of $\mathcal{O}(10^{-4})$ for the coefficient $-1/2$ of the term $g_{μν}R$ in the Einstein field equations of general relativity (guaranteeing the local energy-momentum conservation). We explore the consequences led by the Rastall gravity on the cosmological parameters in the light of the observational analyses. It turns out that the effective source dynamically screens the usual vacuum energy at high redshifts, but this mechanism barely works due to the opposition by the altered evolution of CDM. Consequently, two simultaneous modifications of different nature in the Friedmann equation act against each other, and do not help to considerably relax the so-called low redshift tensions. Our results may offer a guide for the research community that studies the Rastall gravity in various aspects of gravitation and cosmology.
The Rastall's theory is a modification of General Relativity touching one of the cornestone of gravity theory: the conservation laws. In Rastall's theory, the energy-momentum tensor is not conserved anymore, depending now on the gradient of the Ricci curvature. In this sense, this theory can be seen as a classical implementation of quantum effects in a curved background space-time. We exploit this structure in order to reproduce some results of an effective theory of quantum loop cosmology. Later, we propose a model for the dark sector of the universe. In this case, the corresponding $Λ$CDM mo…
Rastall's theory is a modification of General Relativity, based on the non-conservation of the stress-energy tensor. The latter is encoded in a parameter $γ$ such that $γ= 1$ restores the usual $\nabla_νT^{μν} = 0$ law. We test Rastall's theory in cosmology, on a flat Robertson-Walker metric, investigating a two-fluid model and using the type Ia supernovae Constitution dataset. One of the fluids is pressureless and obeys the usual conservation law, whereas the other is described by an equation of state $p_x = w_xρ_x$, with $w_x$ constant. The Bayesian analysis of the Constitution set does not …
The Rastall gravity is a modification of Einstein's general relativity, in which the energy-momentum conservation is not satisfied and depends on the gradient of the Ricci curvature. It is in dispute whether the Rastall gravity is equivalent to the general relativity (GR). In this work, we constrain the theory using the rotation curves of Low Surface Brightness (LSB) spiral galaxies. Through fitting the rotation curves of LSB galaxies, we obtain the parameter $β$ of the Rastall gravity. The $β$ values of LSB galaxies satisfy Weak Energy Condition (WEC) and Strong Energy Condition(SEC). Combini…
The k-essence theory with a power-law function of $(\partialϕ)^2$ and Rastall's non-conservative theory of gravity with a scalar field are shown to have the same solutions for the metric under the assumption that both the metric and the scalar fields depend on a single coordinate. This equivalence (called k-R duality) holds for static configurations with various symmetries (spherical, plane, cylindrical, etc.) and all homogeneous cosmologies. In the presence of matter, Rastall's theory requires additional assumptions on how the stress-energy tensor non-conservation is distributed between diffe…
Impact of Rastall gravity on hydrostatic mass of galaxy clusters
Institut Teknologi Bandung（万隆理工学院）；Indonesia Center for Theoretical and Mathematical Physics (ICTMP)（印度尼西亚理论与数学物理中心）；Universitas Pendidikan Indonesia（印度尼西亚教育大学）
We confront dark energy models which are currently similar to $Λ$CDM theory with observational data which include the SNe data, matter density perturbations and baryon acoustic oscillations data. DE cosmology under consideration may evolve to Big Rip, type II or type III future singularity, or to Little Rip or Pseudo-Rip universe. It is shown that matter perturbations data define more precisely the possible deviation from $Λ$CDM model than consideration of SNe data only. The combined data analysis proves that DE models under consideration are as consistent as $Λ$CDM model. We demonstrate that …
The newly released observational $H(z)$ data (OHD) is used to constrain $Λ(t)$CDM models as holographic and agegraphic dark energy. By the use of the length scale and time scale as the IR cut-off including Hubble horizon (HH), future event horizon (FEH), age of the universe (AU), and conformal time (CT), we achieve four different $Λ(t)$CDM models which can describe the present cosmological acceleration respectively. In order to get a comparison between such $Λ(t)$CDM models and standard $Λ$CDM model, we use the information criteria (IC), $Om(z)$ diagnostic, and statefinder diagnostic to measur…
Soft cosmology is an extension of standard cosmology allowing for a scale-dependent equation-of-state (EoS) parameter in the dark sectors, which is one of the properties of soft materials in condensed-matter physics, that may arise either intrinsically or effectively. We use data from Cosmic Microwave Background (CMB), Baryonic Acoustic Oscillations (BAO), Supernovae Type Ia (SNIa), and Redshift space distrotion (RSD) probes, in order to impose observational constraints on soft dark energy and soft dark matter. We examine three simple models, corresponding to the minimum extensions of $Λ$CDM s…
In this work, we consider the so-called $Λ(α)$CDM cosmology with $Λ\proptoα^{-6}$ while the fine-structure "constant" $α$ is varying. In this scenario, the accelerated expansion of the universe is driven by the cosmological "constant" $Λ$ (equivalently the vacuum energy), and the varying $α$ is driven by a subdominant scalar field $ϕ$ coupling with the electromagnetic field. The observational constraints on the varying $α$ and $Λ\proptoα^{-6}$ models with various couplings $B_F(ϕ)$ between the subdominant scalar field $ϕ$ and the electromagnetic field are considered.
We present a comprehensive and updated comparison with cosmological observations of two non-local modifications of gravity previously introduced by our group, the so called RR and RT models. We implement the background evolution and the cosmological perturbations of the models in a modified Boltzmann code, using CLASS. We then test the non-local models against the {\em Planck} 2015 TT, TE, EE and Cosmic Microwave Background (CMB) lensing data, isotropic and anisotropic Baryonic Acoustic Oscillations (BAO) data, JLA supernovae, $H_0$ measurements and growth rate data, and we perform Bayesian pa…
Using a new recently compiled milliarcsecond compact radio data set of 120 intermediate-luminosity quasars in the redshift range $0.46< z <2.76$, whose statistical linear sizes show negligible dependence on redshifts and intrinsic luminosity and thus represent standard rulers in cosmology, we constrain three viable and most popular $f(T)$ gravity models, where $T$ is the torsion scalar in teleparallel gravity. Our analysis reveals that constraining power of the quasars data (N=120) is comparable to the Union2.1 SN Ia data (N=580) for all three $f(T)$ models. Together with other standard ruler …
Most dark energy models have the $Λ$CDM as their limit, and if future observations constrain our universe to be close to $Λ$CDM Bayesian arguments about the evidence and the fine-tuning will have to be employed to discriminate between the models. Assuming a baseline $Λ$CDM model we investigate a number of quintessence and phantom dark energy models, and we study how they would perform when compared to observational data, such as the expansion rate, the angular distance, and the growth rate measurements, from the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. We sample posterior l…
The consistency of some dynamical dark energy models based on Gauss-Bonnet invariant, ${\cal G}$, is studied compared with cosmological observational tests. The investigated models are modified form of Gauss Bonnet dark energy, MGB-DE and two other versions which are interacting MGB and $n_0$MGB. The energy density of proposed models are combinations of powers of the Hubble rate, H, and its time derivative. To inquire the performance of MGB dark energy models, we have used data analyzing methods and numerical solutions, in both background and perturbed levels, based on recent observational dat…
In this work we examine the recently proposed phenomenological emergent dark energy (PEDE) model by \cite{Li:2019yem}, using the latest observational data in both expansion and perturbation levels. Applying the statistical Bayesian evidence as well as the AIC and BIC information criteria, we compare the PEDE model with the concordance $Λ$CDM model in both flat and non-flat universes. We combine the observational datasets as (i) expansion data (except CMB), (ii) expansion data (including CMB) and (iii) expansion data jointed to the growth rate dataset. Our statistical results show that the flat…
We present an analysis of the Brans-Dicke cosmological model with a cosmological constant and cold dark matter (BD-$Λ$CDM). We find that the BD-$Λ$CDM is favored by the overall cosmological data (SNIa+BAO+$H(z)$+LSS+CMB) when it is compared with the standard model of cosmology. The BD-$Λ$CDM model can be viewed from the GR perspective as a Running Vacuum Model (RVM) with a time evolving vacuum energy density. Due to this fact and also to its time evolving effective gravitational coupling, the model can alleviate the $σ_8$ and the $H_0$ tensions at a time. We also present the results for differ…
We study the cosmology of a specific class of nonlocal model of modified gravity, the so-called Deser-Woodard (DW) model, modifying the Einstein-Hilbert action by a term $\sim R f(\Box^{-1}R)$, where $f$ is a free function. Choosing $f$ so as to reproduce the $Λ{\rm CDM}$ cosmological background expansion history within the nonlocal model, we implement the model in a cosmological linear Einstein--Boltzmann solver and study the deviations to GR the model induces in the scalar and tensor perturbations. We observe that the DW nonlocal model describes a modified propagation for the gravitational w…
We propose a new framework for studying the cosmology of $f(R)$ gravity which completely avoids using the reconstruction programme. This allows us to easily obtain a qualitative feel of how much the $Λ$CDM model differs from other $f(R)$ theories of gravity at the level of linear perturbation theory for theories that share the same background dynamics. This is achieved by using the standard model independent cosmographic parameters to develop a new dynamical system formulation of $f(R)$ gravity which is free from the limitation of having to first specify the functional form of $f(R)$. By consi…
We use observations related to the variation of fundamental constants, in order to impose constraints on the viable and most used $f(T)$ gravity models. In particular, for the fine-structure constant we use direct measurements obtained by different spectrographic methods, while for the effective Newton's constant we use a model-dependent reconstruction, using direct observational Hubble parameter data, in order to investigate its temporal evolution. We consider two $f(T)$ models and we quantify their deviation from $Λ$CDM cosmology through a sole parameter. Our analysis reveals that this param…
We study the $Λ(α)$CDM models with $Λ(α)$ being a function of the time-varying fine structure constant $α$. We give a close look at the constraints on two specific $Λ(α)$CDM models with one and two model parameters, respectively, based on the cosmological observational measurements along with 313 data points for the time-varying $α$. We find that the model parameters are constrained to be around $10^{-4}$, which are similar to the results discussed previously but more accurately.
We study the cosmological predictions of two recently proposed non-local modifications of General Relativity. Both models have the same number of parameters as $Λ$CDM, with a mass parameter $m$ replacing the cosmological constant. We implement the cosmological perturbations of the non-local models into a modification of the CLASS Boltzmann code, and we make a full comparison to CMB, BAO and supernova data. We find that the non-local models fit these datasets as well as $Λ$CDM. For both non-local models parameter estimation using Planck+JLA+BAO data gives a value of $H_0$ higher than in $Λ$CDM,…
Observational Insights on DBI K-essence Models Using Machine Learning and Bayesian Analysis
University of Calcutta（加尔各答大学）；Haldia Government College（霍尔迪亚政府学院）；K. J. Somaiya College of Science and Commerce（K.J. 索马亚科学与商业学院）；Ben-Gurion University of the Negev（内盖夫本-古里安大学）；Frankfurt Institute for Advanced Studies (FIAS)（法兰克福高等研究所）；Bahamas Advanced Study Institute and Conferences（巴哈马高级研究院与会议）；Sister Nivedita University（尼维迪塔姐妹大学）；Prabhat Kumar College（普拉巴特·库马尔学院）；Institute of Astronomy, Space and Earth Science（天文学、空间与地球科学研究院）
We use the physically-consistent tilted spatially-flat and untilted non-flat $Λ$CDM inflation models to constrain cosmological parameter values with the Planck 2015 cosmic microwave background (CMB) anisotropy data and recent Type Ia supernovae measurements, baryonic acoustic oscillations (BAO) data, growth rate observations, and Hubble parameter measurements. The most dramatic consequence of including the four non-CMB data sets is the significant strengthening of the evidence for non-flatness in the non-flat $Λ$CDM model, from 1.8$σ$ for the CMB data alone to 5.1$σ$ for the full data combinat…
We show that primordial black holes can be produced from the collapse of large isocurvature perturbations of the cold dark matter. We develop a novel procedure to compute the resulting black hole abundance by studying matched perturbations of matter-only universes, and we use our procedure to translate observational constraints on black hole abundances into model-independent constraints on cold dark matter isocurvature perturbations over a wide range of scales. The constraint on the typical amplitude of the primordial perturbations weakens slightly slower than linearly on small scales.
Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens（雅典国家天文台天文学、天体物理学、空间应用与遥感研究所）；Departamento de Matemáticas, Universidad Católica del Norte（北天主教学院数学系）；CAS Key Laboratory for Research in Galaxies and Cosmology, School of Astronomy and Space Science, University of Science and Technology of China（中国科学院星系与宇宙学重点实验室，中国科学技术大学天文与空间科学学院）
We perform a detailed confrontation of various oscillating dark-energy parame-trizations with the latest sets of observational data. In particular, we use data from Joint Light Curve analysis (JLA) sample from Supernoave Type Ia, Baryon Acoustic Oscillations (BAO) distance measurements, Cosmic Microwave Background (CMB) observations, redshift space distortion, weak gravitational lensing, Hubble parameter measurements from cosmic chronometers, and we impose constraints on four oscillating models. From the analyses we find that the best-fit characters of almost all models are bent towards the ph…
We constrain spatially-flat tilted and nonflat untilted scalar field ($ϕ$) dynamical dark energy inflation ($ϕ$CDM) models by using Planck 2015 cosmic microwave background (CMB) anisotropy measurements and recent baryonic acoustic oscillation distance observations, Type Ia supernovae apparent magnitude data, Hubble parameter measurements, and growth rate data. We assume an inverse power-law scalar field potential energy density $V(ϕ)=V_0 ϕ^{-α}$. We find that the combination of the CMB data with the four non-CMB data sets significantly improves parameter constraints and strengthens the evidenc…
In the paper, we consider two models in which dark energy is coupled with either dust matter or dark matter, and discuss the conditions that allow more time for structure formation to take place at high redshifts. These models are expected to have a larger age of the universe than that of $Λ$CDM [universe consists of cold dark matter (CDM) and dark energy (a cosmological constant, $Λ$)], so it can explain the formation of high redshift gravitationally bound systems which the $Λ$CDM model cannot interpret. We use the observational Hubble parameter data (OHD) and Hubble parameter obtained from c…
We investigate the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat ΛCDM case, there is only one free parameter to be adjusted by the data in this class of Λ(t)CDM scenarios, namely, the matter density parameter. To perform our analysis we use three of the most recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and th…
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…
Using the latest observational data from Planck-CMB and its combination with the pre-reconstructed full-shape (FS) galaxy power spectrum measurements from the BOSS DR12 sample and eBOSS LRG DR16 sample, we report the observational constraints on the cosmic neutrino properties given by the extended $Λ$CDM scenario: $Λ$CDM + $N_{\rm eff}$ + $\sum m_ν$ + $c^2_{\rm eff}$ + $c^2_{\rm vis}$ + $ξ_ν$, and its particular case $Λ$CDM + $c^2_{\rm eff}$ + $c^2_{\rm vis}$ + $ξ_ν$, where $N_{\rm eff}$, $\sum m_ν$, $c^2_{\rm eff}$, $c^2_{\rm vis}$, $ξ_ν$ are the effective number of species, the total neutrin…
Testing the Coexistence of Dark Energy and Dark Matter with Late-time Observational Data
North-West University（西北大学）；National Institute for Theoretical and Computational Sciences (NITheCS)（国家理论与计算科学研究所）；Durban University of Technology（德班理工大学）；Universidad Catòlica del Norte（北方天主教大学）
The unknown physical nature of the Dark Energy motivates in cosmology the study of modifications of the gravity theory at large distances. One of these types of modifications is to consider gravity theories, generally termed as $f(R)$. In this paper we use observational data to both constrain and test the Starobinsky $f(R)$ model \cite{Starobinsky2007}, using updated measurements from the dynamics of the expansion of the universe, $H(z)$; and the growth rate of cosmic structures, $[fσ_8](z)$, where the distinction between the concordance $Λ$CDM model and modified gravity models $f(R)$ becomes …
Planck measurements of the cosmic microwave background power spectra find a lower value of the Hubble constant $H_0$ and a higher value of the fractional matter energy density $Ω_{m0}$ for the concordance $Λ$CDM model, and these results are in tension with other measurements. The {\em Planck} group argued that the tension came either from some sources of unknown systematic errors in some astrophysical measurements or the wrong $Λ$CDM model applied in fitting the data. We studied the reason for the tension on $H_0$ from different measurements by considering two dynamical dark energy models. We …
We use the local value of the Hubble constant recently measured with 2.4% precision, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f(T) gravity models, where T is the torsion scalar in teleparallel gravity. In particular, we consider three f(T) models with two parameters, out of which one is independent, and we quantify their deviation from $Λ$CDM cosmology through a sole parameter. Our analysis reveals that …
The search for the physical mechanism underlying the observational evidence for the acceleration of the recent universe is a compelling goal of modern fundamental cosmology. Here we quantitatively study a class of homogeneous and isotropic cosmological models in which the matter side of Einstein's equations includes, in addition to the canonical term, a term proportional to the trace of the energy-momentum tensor, $T=ρ-3p$, and constrain these models using low redshift background cosmology data. One may think of these models as extensions of general relativity with a nonlinear matter Lagrangia…
We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard $Λ$CDM model, wherein the extension is characterized by two additional degrees of freedom; the BD parameter, $ω$, and the present day density parameter corresponding to the shear scalar, $Ω_{σ^2,0}$. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on $ω$, nam…
We study a generalized version of Chaplygin gas as unified model of dark matter and dark energy. Using realistic theoretical models and the currently available observational data from the age of the universe, the expansion history based on the type Ia supernovae, the matter power spectrum, the cosmic microwave background radiation anisotropy power spectra, and the perturbation growth factor we put the unified model under observational test. As the model has only two free parameters in the flat Friedmann background [$Λ$CDM (cold dark matter) model has only one free parameter] we show that the m…
A Spectrum of Cosmological Rips and Their Observational Signatures
University of the Basque Country UPV/EHU（巴斯克大学）；EHU Quantum Center, University of the Basque Country UPV/EHU（EHU量子中心，巴斯克大学）；Institute of Physics, University of Szczecin（谢切钦大学物理研究所）
The interacting dark matter (IDM) scenario allows for the acceleration of the Universe without Dark Energy. We constrain the IDM model by using the newly revised observational data including $H(z)$ data and Union2 SNe Ia via the Markov chain Monte Carlo method. When mimicking the $Λ$CDM model, we obtain a more stringent upper limit to the effective annihilation term at $κC_1\approx 10^{-3.4}\rm{Gyr}^{-1}$, and a tighter lower limit to the relevant mass of Dark Matter particles at $M_x\approx 10^{-8.6}\rm{Gev}$. When mimicking the $w$CDM model, we find that the effective equation of state of ID…
We provide an $F(R)$ gravity description of a $Λ$CDM bouncing model, without the need for matter fluids or for cosmological constant. As we explicitly demonstrate, the two cosmological eras that constitute the $Λ$CDM bouncing model, can be generated by $F(R)$ gravity which can lead to accelerating cosmologies. The resulting F(R) gravity has Einstein frame inflationary properties that have concordance to the latest Planck observational data. Both the $F(R)$ gravity stability properties are thoroughly investigated and also, the gravitational particle production, a feature necessary for the viabi…
We investigate in detail some popular cosmological models in light of the latest observational data, including the Union2.1 supernovae compilation, the baryon acoustic oscillation measurements from the WiggleZ Dark Energy Survey, the cosmic microwave background information from the WMAP 7-year observations along with the observational Hubble parameter data. Based on the model selection statistics such as the Akaike and the Bayesian information criterias, we compare different models to assess the worth of them. We do not assume a flat universe in the fitting. Our results show that the concordan…
Aiming at exploring the nature of dark energy, we use thirty-six observational Hubble parameter data (OHD) in the redshift range $0 \leqslant z \leqslant 2.36$ to make a cosmological model-independent test of the two-point $Omh^2(z_{2};z_{1})$ diagnostic. In $Λ$CDM, we have $Omh^2 \equiv Ω_{m}h^2$, where $Ω_{m}$ is the matter density parameter at present. We bin all the OHD into four data points to mitigate the observational contaminations. By comparing with the value of $Ω_{m}h^2$ which is constrained tightly by the Planck observations, our results show that in all six testing pairs of $Omh^2…
We investigate the new observational constraints on $f(T)$ gravity that arise from the effects of primordial gravitational waves (GWs) on the cosmic microwave background (CMB) anisotropies and the BB spectrum. We first show that on the GWs propagation in $f(T)$ gravity we obtain only an amplitude modification and not a phase one, comparing to the case of general relativity in the background of $Λ$CDM cosmology. Concerning primordial GWs we find that the more the model departs from general relativity the larger is the GW amplitude decay, and thus a possible future detection would bring the viab…
