Chevallier Polarski Linder Parametrization Research Articles

Observational Constraints on generalized dark matter properties in the presence of neutrinos with the final Planck release

In this paper, we investigate an extension of the standard ΛCDM model by allowing: a temporal evolution in the equation of state (EoS) of DM via Chevallier–Polarski–Linder parametrization, and the constant non-null sound speed. We also consider the properties of neutrinos, such as the effective neutrino mass and the effective number of neutrino species as free parameters. We derive the constraints on this scenario by using the data from the Planck-2018 cosmic microwave background (CMB), baryonic acoustic oscillation (BAO) measurements, Pantheon+ compilation of Type Ia supernovae (SNe Ia), and some large scale structure (LSS) information from the cosmic shear surveys: Kilo Degree Survey (KiDS)-1000 and Dark Energy Survey (DES). We find constraints on the EoS and sound speed of DM very close to the null value in all the analyses, and thus no significant evidence is found beyond the standard CDM paradigm. In all the analyses, we find the significantly tight upper bounds on the sum of neutrino masses, and significantly lower mean values of S8, which are in agreement with the LSS measurements. Thus, the well-known S8 tension is reconciled in the considered model.

Dark energy constraint on equation of state parameter in the Weyl type [formula omitted] gravity

The equation of state parameter is a significant method for characterizing dark energy models. We investigate the evolution of the equation of state parameter with redshift using a Bayesian analysis of recent observational datasets (the Cosmic Chronometer data (CC) and Pantheon samples). The Chevallier–Polarski–Linder parametrization of the effective equation of state parameter, ωeff=ω0+ωaz1+z, where ω0 and ωa are free constants, is confined to the Weyl type f(Q,T) gravity, where Q represents the non-metricity and T is the trace of the energy–momentum tensor. We observe the evolution of the deceleration parameter q, the density parameter ρ, the pressure p, and the effective equation of state parameter ω. The cosmic data limit for ω does not exclude the possibility of ω<−1. It is seen that the parameter ω shows a transition from deceleration to acceleration, as well as a shift from ω>−1 to ω<−1.

Prospects of high redshift constraints on dark energy models with the Ep, i − Eiso correlation in long gamma ray bursts

ABSTRACT So far large and different data sets revealed the accelerated expansion rate of the Universe, which is usually explained in terms of dark energy. The nature of dark energy is not yet known, and several models have been introduced: a non-zero cosmological constant, a potential energy of some scalar field, effects related to the non-homogeneous distribution of matter, or effects due to alternative theories of gravity. Recently, a tension with the flat ΛCDM model has been discovered using a high-redshift Hubble diagram of supernovae, quasars, and gamma-ray bursts (GRB). Here we use the Union2 type Ia supernovae and GRB Hubble diagram, and a set of direct measurements of the Hubble parameter to explore different dark energy models. We use the Chevallier–Polarski–Linder parametrization of the dark energy equation of state, a minimally coupled quintessence scalar field, and, finally, we consider models with dark energy at early times. We perform a statistical analysis based on the Markov chain Monte Carlo method, and explore the probability distributions of the cosmological parameters for each of the competing models. We apply the Akaike Information Criterion to compare these models: our analysis indicates that an evolving dark energy, described by a scalar field with exponential potential seems to be favoured by observational data.

Thermal stability of Chaplygin gas models and Chevallier–Polarski–Linder parametrization

We consider the fractal universe model with timelike fractal profile in flat Friedmann–Robertson–Walker (FRW) universe model and check the thermodynamic stability of various dark energy models. These dark energy models include family of Chaplygin gas models (such as generalized Chaplygin gas, modified Chaplygin gas, generalized cosmic Chaplygin gas, variable modified Chaplygin gas) and parametrized equation-of-state (Chevallier–Polarski–Linder) model. To check the stability of these models in fractal framework thermodynamically, we construct total equation-of-state parameter for each case. The conditions to check the stability of models depending on some thermodynamic quantities yield three conditions on this parameter. We graphically check the behavior of the equation-of-state parameter along with stability of each model. It is concluded that the dark energy models are thermodynamically stable under appropriate choices of model parameters.

Model-independent calibrations of gamma-ray bursts using machine learning

ABSTRACT We alleviate the circularity problem, whereby gamma-ray bursts are not perfect distance indicators, by means of a new model-independent technique based on Bézier polynomials. We use the well consolidate Amati and Combo correlations. We consider improved calibrated catalogues of mock data from differential Hubble rate points. To get our mock data, we use those machine learning scenarios that well adapt to gamma-ray bursts, discussing in detail how we handle small amounts of data from our machine learning techniques. We explore only three machine learning treatments, i.e. linear regression, neural network, and random forest, emphasizing quantitative statistical motivations behind these choices. Our calibration strategy consists in taking Hubble’s data, creating the mock compilation using machine learning and calibrating the aforementioned correlations through Bézier polynomials with a standard chi-square analysis first and then by means of a hierarchical Bayesian regression procedure. The corresponding catalogues, built up from the two correlations, have been used to constrain dark energy scenarios. We thus employ Markov chain Monte Carlo numerical analyses based on the most recent Pantheon supernova data, baryonic acoustic oscillations, and our gamma-ray burst data. We test the standard ΛCDM model and the Chevallier–Polarski–Linder parametrization. We discuss the recent H0 tension in view of our results. Moreover, we highlight a further severe tension over Ωm and we conclude that a slight evolving dark energy model is possible.

Testing the warmness of dark matter

ABSTRACT Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard Λ cold dark matter (ΛCDM) model to the astrophysical and cosmological data. In this paper, we investigate two extended properties of DM: a possible time dependence of the equation of state of DM via Chevallier–Polarski–Linder parametrization, wdm = wdm0 + wdm1(1 − a), and the constant non-null sound speed $\hat{c}^2_{\rm s,dm}$. We analyse these DM properties on top of the base ΛCDM model by using the data from Planck cosmic microwave background (CMB) temperature and polarization anisotropy, baryonic acoustic oscillations (BAOs), and the local value of the Hubble constant from the Hubble Space Telescope (HST). We find new and robust constraints on the extended free parameters of DM. The most tight constraints are imposed by CMB+BAO data, where the three parameters wdm0, wdm1, and $\hat{c}^2_{\rm s,dm}$ are, respectively, constrained to be less than 1.43 × 10−3, 1.44 × 10−3, and 1.79 × 10−6 at 95 per cent CL. All the extended parameters of DM show consistency with zero at 95 per cent CL, indicating no evidence beyond the CDM paradigm. We notice that the extended properties of DM significantly affect several parameters of the base ΛCDM model. In particular, in all the analyses performed here, we find significantly larger mean values of H0 and lower mean values of σ8 in comparison to the base ΛCDM model. Thus, the well-known H0 and σ8 tensions might be reconciled in the presence of extended DM parameters within the ΛCDM framework. Also, we estimate the warmness of DM particles as well as its mass scale, and find a lower bound: ∼500 eV from our analyses.

Thermodynamics in loop quantum cosmology with non-canonical scalar field model

The cosmological scenario is built up within the framework of scalar field model possessing a noncanonical kinetic term in loop quantum gravity. The noncanonical scalar field is permitted to interact with dark matter field by assuming a specific form of coupling term. The equation of state parameter is set to be constant as well as variable (Chevallier–Polarski–Linder parametrization) and evaluated the behavior of universe through deceleration parameter and weak energy condition. These parameters favor the accelerated expansion of the universe for three values of equation of state parameter in both cases allowed by observational data. The squared speed of sound leads to the stability of the underlying models in both forms of equation of state parameter. Moreover, the validity of generalized second law of thermodynamics is analyzed by using first law of thermodynamics and assume the universe to be enclosed by apparent horizon. The Bekenstein, logarithmic and power-law entropy is being considered as entropy of horizon. The thermodynamic equilibrium condition is also discussed for all three cases of entropies. The generalized second law of thermodynamics and thermal equilibrium condition is satisfied for all the three types of entropies.

Cosmological implications of non-canonical scalar field model in fractal universe

Abstract The cosmological parameters as well as generalized second law of thermodynamics are investigated in the framework of fractal universe taking flat FRW universe filled with scalar field dark energy possessing a non-canonical kinetic term. The non-canonical scalar field model is allowed to interact with dark matter by assuming a specified form of coupling term. With the assumption that the universe is enveloped by apparent horizon, we investigate the validity of generalized second law of thermodynamics by using first law of thermodynamics as well as Bekenstein, logarithmic and power-law horizon entropies. For the illustration of results in more clear way, we set the equation of state parameter as constant as well as variable (Chevallier–Polarski–Linder parametrization). In the above mentioned scenario, the results of cosmological quantities such as squared speed of sound, weak energy condition and deceleration parameter are interpreted for both cases of equation of state parameter and found their compatibility with recent observations. It is also found that the generalized second law of thermodynamics holds for all cases of horizon entropies as well as equation of state parameters under specific constant parameters. The thermodynamic equilibrium is also observed for all cases of entropies.

Mapping the Chevallier-Polarski-Linder parametrization onto physical dark energy Models

We examine the Chevallier-Polarski-Linder (CPL) parametrization, in the context of quintessence and barotropic dark energy models, to determine the subset of such models to which it can provide a good fit. The CPL parametrization gives the equation of state parameter $w$ for the dark energy as a linear function of the scale factor $a$, namely $w = w_0 + w_a(1-a)$. In the case of quintessence models, we find that over most of the $w_0$, $w_a$ parameter space the CPL parametrization maps onto a fairly narrow form of behavior for the potential $V(\phi)$, while a one-dimensional subset of parameter space, for which $w_a = \kappa (1+w_0)$, with $\kappa$ constant, corresponds to a wide range of functional forms for $V(\phi)$. For barotropic models, we show that the functional dependence of the pressure on the density, up to a multiplicative constant, depends only on $w_i = w_a + w_0$ and not on $w_0$ and $w_a$ separately. Our results suggest that the CPL parametrization may not be optimal for testing either type of model.

Probing the matter and dark energy sources in a viable Big Rip model of the Universe

Chevallier–Polarski–Linder (CPL) parametrization for the equation of state (EoS) of dark energy in terms of cosmic redshift or scale factor have been frequently studied in the literature. In this study, we consider cosmic time-based CPL parametrization for the EoS parameter of the effective cosmic fluid that fills the fabric of spatially flat and homogeneous Robertson–Walker (RW) spacetime in General Relativity. The model exhibits two worthy features: (i) It fits the observational data from the latest H(z) and Union 2.1 SN Ia compilations matching the success of ΛCDM model. (ii) It describes the evolution of the Universe from the matter-dominated phase to the recent accelerating phase similar to the ΛCDM model but leads to Big Rip end of the Universe contrary to the everlasting de Sitter expansion in the ΛCDM model. We investigate the matter and dark energy sources in the model, in particular, behavior of the dynamical dark energy responsible for the Big Rip end of Universe.

Fitting the constitution type Ia supernova data with the redshift-binned parametrization method

In this work, we explore the cosmological consequences of the recently released Constitution sample of 397 Type Ia supernovae (SNIa). By revisiting the Chevallier-Polarski-Linder (CPL) parametrization, we find that, for fitting the Constitution set alone, the behavior of dark energy (DE) significantly deviates from the cosmological constant Lambda, where the equation of state (EOS) w and the energy density rho(Lambda) of DE will rapidly decrease along with the increase of redshift z. Inspired by this clue, we separate the redshifts into different bins, and discuss the models of a constant w or a constant rho(Lambda) in each bin, respectively. It is found that for fitting the Constitution set alone, w and rho(Lambda) will also rapidly decrease along with the increase of z, which is consistent with the result of CPL model. Moreover, a step function model in which rho(Lambda) rapidly decreases at redshift z similar to 0: 331 presents a significant improvement (Delta chi(2) = -4.361) over the CPL parametrization, and performs better than other DE models. We also plot the error bars of DE density of this model, and find that this model deviates from the cosmological constant Lambda at 68.3% confidence level (CL); this may arise from some biasing systematic errors in the handling of SNIa data, or more interestingly from the nature of DE itself. In addition, for models with same number of redshift bins, a piecewise constant rho(Lambda) model always performs better than a piecewise constant w model; this shows the advantage of using rho(Lambda), instead of w, to probe the variation of DE.

Test of the Chevallier-Polarski-Linder parametrization for rapid dark energy equation of state transitions

We test the robustness and flexibility of the Chevallier-Polarski-Linder (CPL) parametrization of the dark energy equation of state w(z)=w{sub 0}+w{sub a}(z/1+z) in recovering a four-parameter steplike fiducial model. We constrain the parameter space region of the underlying fiducial model where the CPL parametrization offers a reliable reconstruction. It turns out that non-negligible biases leak into the results for recent (z<2.5) rapid transitions, but that CPL yields a good reconstruction in all other cases. The presented analysis is performed with supernova Ia data as forecasted for a space mission like SNAP/JDEM, combined with future expectations for the cosmic microwave background shift parameter R and the baryonic acoustic oscillation parameter A.

Is the dynamics of scaling dark energy detectable?

We highlight the unexpected impact of nucleosynthesis and other early universe constraintson the detectability of scaling quintessence dynamics at late times, showing that suchdynamics may well be invisible until the unveiling of the Stage-IV dark energy experiments(DUNE, JDEM, LSST, SKA). Nucleosynthesis strongly limits potential deviations fromΛCDM. Surprisingly, the standard Chevallier–Polarski–Linder parametrization,w(z) = w0+waz/(1+z), cannot match the nucleosynthesis bound for minimally coupled scaling fields. Given thatsuch models are arguably the best-motivated alternatives to a cosmological constant theseresults may significantly impact future cosmological survey design and imply that darkenergy may well be dynamical even if we do not detect any dynamics in the nextdecade.