X-ray Gas Mass Fraction Research Articles

Probing the dark matter density evolution law with large scale structures

We propose a new method to explore a possible departure from the standard time evolution law for the dark matter density. We looked for a violation of this law by using a deformed evolution law, given by rho _c(z) propto (1+z)^{3+epsilon }, and then constrain epsilon . The dataset used for this purpose consists of Strong Gravitational Lensing data obtained from SLOAN Lens ACS, BOSS Emission-line Lens Survey, Strong Legacy Survey SL2S, and SLACS; along with galaxy cluster X-ray gas mass fraction measurements obtained using the Chandra Telescope. Our analyses show that epsilon is consistent with zero within 1 sigma c.l., but the current dataset cannot rule out with high confidence level interacting models of dark matter and dark energy.

Scalar Tensor Cosmology With Kinetic, Gauss-Bonnet and Nonminimal Derivative Couplings and Supersymmetric Loop Corrected Potential

We discuss a particular four-dimensional cosmology based on non-minimal scalar tensor theories characterized by a supersymmetric loop corrected potential and a Hubble parameter defined as a function of the scalar field. Power-law solutions are obtained in the FRW background giving rise to acceleratedly expanding universe characterized by a scale factor and a scalar field depending both on the non-minimal coupling parameter ξ. Based on SNeIa data and on Hubble data X-ray gas mass fraction measurements, we find 0.116 < ξ < 0.225 which results on a universe dominated by vacuum energy.

X-ray surface brightness observations of galaxy clusters, cosmic opacity and the limits on the matter density parameter

In this work, we use two gas mass fraction samples of galaxy clusters obtained from their X-ray surface brightness observations jointly with recent H(z) data in a flat ΛCDM framework to impose limits on cosmic opacity. {It is assumed that the galaxy clusters are in hydrostatic equilibrium and their gas mass fraction measurement is constant with redshift.} We show that the current limits on the matter density parameter obtained from X-ray gas mass fraction test are strongly dependent on the cosmic transparency assumption even for a flat scenario. Our results are consistent with a transparent universe within 1σ c.l. in full agreement with other analyses which used type Ia supernovae, gamma ray burst and H(z) data.

Is the non-isothermal double β-model incompatible with no time evolution of galaxy cluster gas mass fraction?

In this paper, we propose a new method to obtain the depletion factor γ(z), the ratio by which the measured baryon fraction in galaxy clusters is depleted with respect to the universal mean. We use exclusively galaxy cluster data, namely, X-ray gas mass fraction (fgas) and angular diameter distance measurements from Sunyaev–Zel’dovich effect plus X-ray observations. The galaxy clusters are the same in both data set and the non-isothermal spherical double β-model was used to describe their electron density and temperature profiles. In order to compare our results with those from recent cosmological hydrodynamical simulations, we suppose a possible time evolution for γ(z), such as, γ(z)=γ0(1+γ1z). As main conclusions we found that: the γ0 value is in full agreement with the simulations. On the other hand, although the γ1 value found in our analysis is compatible with γ1=0 within 2σ c.l., our results show a non-negligible time evolution for the depletion factor, unlike the results of the simulations. However, we also put constraints on γ(z) by using the fgas measurements and angular diameter distances obtained from the flat ΛCDM model (Planck results) and from a sample of galaxy clusters described by an elliptical profile. For these cases no significant time evolution for γ(z) was found. Then, if a constant depletion factor is an inherent characteristic of these structures, our results show that the spherical double β-model used to describe the galaxy clusters considered does not affect the quality of their fgas measurements.

Searching for deviations from the general relativity theory with gas mass fraction of galaxy clusters and complementary probes

Nowadays, thanks to the improved precision of cosmological data, it has been possible to search for deviation from the general relativity theory with tests on large cosmic scales. Particularly, there is a class of modified gravity theories that breaks the Einstein equivalence principle (EEP) in the electromagnetic sector, generating variations of the fine structure constant, violations of the cosmic distance duality relation and the evolution law of the cosmic microwave background (CMB) radiation. In recent papers, this class of theories has been tested with angular diameter distances from galaxy clusters, type Ia supernovae and CMB temperature. In this work we propose a new test by considering the most recent X-ray surface brightness observations of galaxy clusters jointly with type Ia supernovae and CMB temperature. {The crucial point here is that we take into account the dependence of the X-ray gas mass fraction of galaxy clusters on possible variations of the fine structure constant and violations of the cosmic distance duality relation.} Our basic result is that this new approach is competitive with the previous one and it also does not show significant deviations from the general relativity.

Cosmological constraints and cosmic growth factor for ghost dark energy models in varying G $G$ theories

The Ghost Dark Energy (GDE) model in varying Newton’s gravitational coupling (VG) theories is investigated. We first obtain the cosmological parameters of the model in modified FRW cosmology with varying $G$ and then study the growth of matter perturbations in this formalism. Applying a Markov Chain Monte Carlo (MCMC) simulation and using the recent observational data, including Baryonic Acoustic Oscillation (BAO), the cluster X-ray Gas Mass Fraction (XGMF), Cosmic Microwave Background radiation (CMB), Growth Function for matter perturbation (GF), type Ia supernova (SNIa) and Hubble data, constraint results on GDE model parameters in VG theory are: $\varOmega_{0m}=0.2751^{+0.0104+0.0208}_{-0.0104-0.0195}$ , $\varOmega_{0d}=0.7093^{+0.0123+0.0229}_{-0.0128-0.0245}$ , $\beta=-0.0156^{+0.0041+0.0082}_{-0.0042-0.0078}$ and $H_{0}=67.444^{+0.899+1.757}_{-0.873-1.829}$ . The results for concordance $\varLambda \mathrm{CDM}$ model are: $\varOmega_{0m}=0.2762^{+0.0097+0.0196}_{-0.0099-0.0188}$ , $\varOmega_{0d}=0.7238^{+0.0099+0.0188}_{-0.0097-0.0196}$ , and $H_{0}=70.265^{+0.797+1.575}_{-0.797-1.515}$ . We show that in this model the universe begins to accelerate at redshift $z_{t}\simeq0.4$ consistently in $1\sigma$ level with observations. It shows that the growth rate of this model is well fitted by observational growth data as the $\varLambda \mathrm{CDM}$ model.

Observational constraints on a phenomenological $$f\left( R,\partial R\right) $$ f R , ∂ R -model

This paper analyses the cosmological consequences of a modified theory of gravity whose action integral is built from a linear combination of the Ricci scalar $R$ and a quadratic term in the covariant derivative of $R$. The resulting Friedmann equations are of the fifth-order in the Hubble function. These equations are solved numerically for a flat space section geometry and pressureless matter. The cosmological parameters of the higher-order model are fit using SN Ia data and X-ray gas mass fraction in galaxy clusters. The best-fit present-day $t_{0}$ values for the deceleration parameter, jerk and snap are given. The coupling constant $\beta$\ of the model is not univocally determined by the data fit, but partially constrained by it. Density parameter $\Omega_{m0}$ is also determined and shows weak correlation with the other parameters. The model allows for two possible future scenarios: there may be either a premature Big Rip or a Rebouncing event depending on the set of values in the space of parameters. The analysis towards the past performed with the best-fit parameters shows that the model is not able to accommodate a matter-dominated stage required to the formation of structure.

Cosmological constraints on ghost dark energy in the Brans–Dicke theory by using MCMC approach

By using a Markov Chain Monte Carlo simulation, we investigate cosmological constraints on the ghost dark energy (GDE) model in the framework of the Brans–Dicke (BD) theory. A combination of the latest observational data of the cosmic microwave background radiation data from seven-year WMAP, the baryon acoustic oscillation data form the SDSS, the supernovae type Ia data from the Union2 and the X-ray gas mass fraction data from the Chandra X-ray observations of the largest relaxed galaxy clusters are used to perform constraints on GDE in the BD cosmology. In this paper, we consider both flat and non-flat universes together with interaction between dark matter and dark energy. The main cosmological parameters are obtained as: Ωbh2=0.0223−0.0013+0.0016, Ωch2=0.1149−0.0104+0.0088 and Ωk=0.0005−0.0073+0.0025. In addition, the Brans–Dicke parameter ω is estimated as 1/ω≃0.002.

Observational constraints on G-corrected holographic dark energy using a Markov chain Monte Carlo method

We constrain holographic dark energy (HDE) with time varying gravitational coupling constant in the framework of the modified Friedmann equations using cosmological data from type Ia supernovae, baryon acoustic oscillations, cosmic microwave background radiation and X-ray gas mass fraction. Applying a Markov Chain Monte Carlo (MCMC) simulation, we obtain the best fit values of the model and cosmological parameters within 1σ confidence level (CL) in a flat universe as: $\varOmega_{b}h^{2}=0.0222^{+0.0018}_{-0.0013}$ , $\varOmega_{c}h^{2}=0.1121^{+0.0110}_{-0.0079}$ , $\alpha_{G}\equiv \dot{G}/(HG) =0.1647^{+0.3547}_{-0.2971}$ and the HDE constant $c=0.9322^{+0.4569}_{-0.5447}$ . Using the best fit values, the equation of state of the dark component at the present time w d0 at 1σ CL can cross the phantom boundary w=−1.

Testing X-ray measurements of galaxy cluster gas mass fraction using the cosmic distance-duality relation

We propose a consistency test for some recent X-ray gas mass fraction (fgas) measurements in galaxy clusters, using the cosmic distance-duality relation, ηtheory = DL(1 + z)−2/DA, with luminosity distance (DL) data from the Union2 compilation of type Ia supernovae. We set ηtheory ≡ 1, instead of assigning any redshift parameterizations to it, and constrain the cosmological information preferred by fgas data along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al. (two samples), LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Allen et al.'s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.'s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.'s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an ΩΛ = 0 cosmology.

An interacting dark energy model in a non-flat universe

In this paper, an interacting dark energy model in a non-flat universe is studied, with taking interaction form $$C=\alpha H\rho _{de}$$ . And in this study a property for the mysterious dark energy is aforehand assumed, i.e. its equation of state $$w_{\Lambda }=-1$$ . After several derivations, a power-law form of dark energy density is obtained $$\rho _{\Lambda } \propto a^{-\alpha }$$ , here $$a$$ is the cosmic scale factor, $$\alpha $$ is a constant parameter introducing to describe the interaction strength and the evolution of dark energy. By comparing with the current cosmic observations, the combined constraints on the parameter $$\alpha $$ is investigated in a non-flat universe. For the used data they include: the Union2 data of type Ia supernova, the Hubble data at different redshifts including several new published datapoints, the baryon acoustic oscillation data, the cosmic microwave background data, and the observational data from cluster X-ray gas mass fraction. The constraint results on model parameters are $$\Omega _{K}=0.0024\,(\pm 0.0053)^{+0.0052+0.0105}_{-0.0052-0.0103}, \alpha =-0.030\,(\pm 0.042)^{+0.041+0.079}_{-0.042-0.085}$$ and $$\Omega _{0m}=0.282\,(\pm 0.011)^{+0.011+0.023}_{-0.011-0.022}$$ . According to the constraint results, it is shown that small constraint values of $$\alpha $$ indicate that the strength of interaction is weak, and at $$1\sigma $$ confidence level the non-interacting cosmological constant model can not be excluded.

Interacting generalized ghost dark energy in a non-flat universe

AbstractWe investigate the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity. First, we study the non-interacting generalized ghost dark energy in a flat Friedmann-Robertson-Walker (FRW) background. We obtain the equation of state parameter, w D = p/ρ, the deceleration parameter, and the evolution equation of the generalized ghost dark energy. We find that, in this case, w D cannot cross the phantom line (w D &gt; −1) and eventually the universe approaches a de-Sitter phase of expansion (w D → −1). Then, we extend the study to the interacting ghost dark energy in both a flat and non-flat FRW universe. We find that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (w D &lt; −1) provided the parameters of the model are chosen suitably. Finally, we constrain the model parameters by using the Markov Chain Monte Carlo (MCMC) method and a combined dataset of SNIa, CMB, BAO and X-ray gas mass fraction.

An accelerated universe from Brans-Dicke theory in the Einstein frame

The current acceleration of the universe is not consistent with the theory of general relativity (GR). The substitutes of GR have been studied widely. One of them is the Brans-Dicke (BD) theory. Thereinto, most studies of BD theory are in the frame of Jordan representation. In this paper we investigate the accelerating cosmology from BD theory in the other frame, i.e. in the Einstein frame, where it indicates the interaction between the matter and the BD scalar field. We apply the Markov Chain Monte Carlo method to study the cosmic constraints on BD theory according to the current experiment data from the kinematical observations: the Union2 dataset of type supernovae Ia (SNIa) and the observational Hubble data (OHD), and the dynamical observations: the baryon acoustic oscillation (BAO), the cosmic microwave background (CMB) data, and the cluster X-ray gas mass fraction. It is shown that an expanded universe from deceleration to acceleration is given in this theory. And the constraint results on BD model parameters are β = −0.0067(±0.2268) −0.2372−0.4407 +0.2395+0.4168 , γ = 0.0237(±0.0342) −0.0329−0.0647 +0.0326+0.0715 , e = −0.0063(±0.0073) −0.0073−0.0130 +0.0072+0.0158 ; and the constraints values of some correlative cosmological parameters are the dimensionless matter density Ω 0m = 0.2853(±0.0132) −0.0133−0.0247 +0.0132+0.0262 , the cosmic age = 13.5699(±0.2398) −0.2374−0.4568 +0.2371+0.4806 Gyr, and the current Hubble parameter H 0 = 70.2623(±1.2695) −1.2675−2.5150 +1.2749+2.4532 .

A matter-dominated cosmological model with variable G and Λ and its confrontation with observational data

In the framework of renormalization-group improved cosmologies, we analyze both theoretically and observationally the exact and general solution of the matter-dominated cosmological equations, using the expression of \Lambda = \Lambda(G) already determined by the integration method employed in a previous paper. A rough comparison between such a model and the concordance \LambdaCDM model as to the magnitude-redshift relationship has been already done, without showing any appreciable differences. We here perform a more refined study of how astrophysical data (Union2 set) on type-I supernovae, gamma ray bursts (in a sample calibrated in a model independent way with the SneIa dataset), and gas fraction in galaxy clusters (using a sample of Chandra measurements of the X-ray gas mass fraction) affect the model and constrain its parameters. We also apply a cosmographic approach to our cosmological model and estimate the cosmographic parameters by fitting both the supernovae and the gamma ray bursts datasets. We show that this matter-dominated cosmological model with variable Newton parameter and variable cosmological term is indeed compatible with the observations above (on type Ia supernovae, the gamma ray bursts Hubble diagram, and the gas mass fraction in X-ray luminous galaxy clusters). The cosmographic approach adopted confirms such conclusions. Finally, it seems possible to include radiation into the model, since numerical integration of the equations derived by the presence of both radiation and matter shows that, after inflation, the total density parameter is initially dominated by the radiation contribution and later by the matter one.

Testing the cosmic distance duality with X-ray gas mass fraction and supernovae data

Abstract In this Letter, we discuss a new cosmological-model-independent test for the cosmic distance duality relation (CDDR), η=DL(L)(1 +z)−2/DA(z) = 1, where DA(z) and DL(z) are the angular diameter and luminosity distances, respectively. Using the general expression for X-ray gas mass fraction (fgas) of galaxy clusters, fgas∝DLDA1/2, we show that fgas observations jointly with Type Ia supernovae (SNe Ia) data furnish a validity test for the CDDR. To perform our analysis, we use 38 fgas measurements recently studied by two groups considering different assumptions to describe the clusters and two subsamples of SNe Ia distance luminosity extracted from the Union2 compilation. In our test, we consider the η parameter as a function of the redshift parametrized by two different functional forms. It is found that the La Roque et al. sample is in perfect agreement with the duality relation (η= 1), whereas the Ettori et al. sample presents a significant conflict.

Cosmological constraints on the generalized holographic dark energy

We use the Markov Chain Monte Carlo method to investigate global constraints on the generalized holographic (GH) dark energy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic dark energy can cross over the phantom boundary w de =−1.

Does accelerating universe indicate Brans-Dicke theory?

The evolution of universe in Brans-Dicke (BD) theory is discussed in this paper. Considering a parameterized scenario for BD scalar field $\phi=\phi_{0}a^{\alpha}$ which plays the role of gravitational "constant" $G$, we apply the Markov Chain Monte Carlo method to investigate a global constraints on BD theory with a self-interacting potential according to the current observational data: Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. It is shown that an expanded universe from deceleration to acceleration is given in this theory, and the constraint results of dimensionless matter density $\Omega_{0m}$ and parameter $\alpha$ are, $\Omega_{0m}=0.286^{+0.037+0.050}_{-0.039-0.047}$ and $\alpha=0.0046^{+0.0149+0.0171}_{-0.0171-0.0206}$ which is consistent with the result of current experiment exploration, $\mid\alpha\mid \leq 0.132124$. In addition, we use the geometrical diagnostic method, jerk parameter $j$, to distinguish the BD theory and cosmological constant model in Einstein's theory of general relativity.

Running coupling: does the coupling between dark energy and dark matter change sign during the cosmological evolution?

In this paper we put forward a running coupling scenario for describing the interaction between dark energy and dark matter. The dark sector interaction in our scenario is free of the assumption that the interaction term $Q$ is proportional to the Hubble expansion rate and the energy densities of dark sectors. We only use a time-variable coupling $b(a)$ (with $a$ the scale factor of the universe) to characterize the interaction $Q$. We propose a parametrization form for the running coupling $b(a)=b_0a+b_e(1-a)$ in which the early-time coupling is given by a constant $b_e$, while today the coupling is given by another constant, $b_0$. For investigating the feature of the running coupling, we employ three dark energy models, namely, the cosmological constant model ($w=-1$), the constant $w$ model ($w=w_0$), and the time-dependent $w$ model ($w(a)=w_0+w_1(1-a)$). We constrain the models with the current observational data, including the type Ia supernova, the baryon acoustic oscillation, the cosmic microwave background, the Hubble expansion rate, and the X-ray gas mass fraction data. The fitting results indicate that a time-varying vacuum scenario is favored, in which the coupling $b(z)$ crosses the noninteracting line ($b=0$) during the cosmological evolution and the sign changes from negative to positive. The crossing of the noninteracting line happens at around $z=0.2-0.3$, and the crossing behavior is favored at about 1$\sigma$ confidence level. Our work implies that we should pay more attention to the time-varying vacuum model and seriously consider the phenomenological construction of a sign-changeable or oscillatory interaction between dark sectors.

Observational constraints to Ricci dark energy model by using: SN, BAO, OHD, fgas data sets

We perform a global constraint on the Ricci darkenergy model with both the flat case and the non-flat case, usingthe Markov Chain Monte Carlo (MCMC) method and the combinedobservational data from the cluster X-ray gas mass fraction,Supernovae of type Ia (397), baryon acoustic oscillations, currentCosmic Microwave Background, and the observational Hubble function.In the flat model, we obtain the best fit values of the parametersin 1σ,2σ regions: Ωm0 = 0.2927+0.0420+0.0542−0.0323−0.0388, α = 0.3823+0.0331+0.0415−0.0418−0.0541, Age/Gyr = 13.48+0.13+0.17−0.16−0.21, H0 = 69.09+2.56+3.09−2.37−3.39. In the non-flatmodel, the best fit parameters are found in 1σ,2σregions:Ωm0 = 0.3003+0.0367+0.0429−0.0371−0.0423,α = 0.3845+0.0386+0.0521−0.0474−0.0523,Ωk = 0.0240+0.0109+0.0133−0.0130−0.0153,Age/Gyr = 12.54+0.51+0.65−0.37−0.49, H0 = 72.89+3.31+3.88−3.05−3.72. Compared to the constraint results in theΛCDM model by using the same datasets, it is shownthat the current combined datasets prefer the ΛCDMmodel to the Ricci dark energy model.

Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach

We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, Ωbh2 = 0.0235+0.0021−0.0018 (1σ) +0.0028−0.0022 (2σ), Ωk = 0.0035+0.0172−0.0182 (1σ) +0.0226−0.0204 (2σ), As = 0.753+0.037−0.035 (1σ) +0.045−0.044 (2σ), α = 0.043+0.102−0.106 (1σ) +0.134−0.117 (2σ), and H0 = 70.00+3.25−2.92 (1σ) +3.77−3.67 (2σ), which is more stringent than the previous results for constraint on GCG model parameters. Furthermore, according to the information criterion, it seems that the current observations much support ΛCDM model relative to the GCG model.