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1.
The Hubble constant(H0), which represents the expansion rate of the universe, is one of the most important cosmological parameters. The recent measurements of H0using the distance ladder methods such as type Ia supernovae are significantly greater than the CMB measurements by Planck. The difference points to a crisis in the standard model of cosmology termed Hubble tension. In this work we compare different cosmological models,determine the Hubble constant and comment on the Hubble te...  相似文献   

2.
We have investigated late time acceleration for a spatially flat dust filled Universe in BransDicke theory in the presence of a positive cosmological constant Λ. Expressions for Hubble's constant,luminosity distance and apparent magnitude have been obtained for our model. The theoretical results are compared with observed values of the latest 287 high redshift(0.3 ≤ z ≤ 1.4) Type Ia supernova data taken from the Union 2.1 compilation to estimate present values of matter and dark energy parameters,(?_m)_0 and(?_Λ)_0. We have also estimated the present value of Hubble's constant H0 in light of an updated sample of Hubble parameter measurements including 19 independent data points. The results are found to be in good agreement with recent astrophysical observations. We also calculated various physical parameters such as matter and dark energy densities, present age of the Universe and deceleration parameter. The value for Brans-Dicke-coupling constant ω is set to be 40 000 based on accuracy of solar system tests and recent experimental evidence.  相似文献   

3.
The validity of the cosmic distance-duality(DD) relation is investigated by using 91 measurements of the gas mass fraction of galaxy clusters recently reported by the Atacama Cosmology Telescope(ACT) and the luminosity distance from the Union2.1 type Ia supernova(SNIa) sample independent of any cosmological models and the value of the Hubble constant. We consider four different approaches to derive the gas mass function and two different parameterizations of the DD relation, and find that they have very slight influences on the DD relation test and the relation is valid at the 1σ confidence level. We also discuss the constraints on α and β, which represent the effects of the shapes and colors of the light curves of SNIa,respectively. Our results on α and β are different from those obtained from the ΛCDM model and the galaxy cluster plus SNIa data.  相似文献   

4.
We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase. This redshift is termed the transition redshift(zt). We use the spatially flat and non-flat variants of the most common ΛCDM and XCDM models to put constraints on the transition redshift along with the other model parameters. The data for this analysis come from the recent and updated Pantheon+ supernova(SN) data set and the Hubble parameter measurements obta...  相似文献   

5.
We investigated the scenario of time-dependent diffusive interaction between dark matter and dark energy and showed that such a model can be accommodated within the observations of luminosity distanceredshift data in Supernova la(SN la)observations.We obtain constraints on different relevant parameters of this model from the observational data.We consider a homogeneous scalar field(t)driven by a k-essence Lagrangian of the form L=V(φ)F(X)with constant potential V(φ)=V,to describe the dynamics of dark energy in this model.Using the temporal behaviour of the FRW scale factor,the equation of state and total energy density of the dark fluid,extracted from the analysis of SN la(JLA)data,we have obtained the time-dependence of the k-essence scalar field and also reconstructed the form of the function F(X)in the k-essence Lagrangian.  相似文献   

6.
We examine the validity of the ΛCDM model and probe the dynamics of dark energy with the latest astronomical observations.Using the Om(z) diagnosis,we find that various kinds of observational data are in tension within the ΛCDM framework.We then allow for dynamics of dark energy and investigate the constraint on dark energy parameters.We find that for two different kinds of parametrisations of the equation of state parameter w,a combination of current data mildly favours an evolving w,although the significance is not sufficient for it to be supported by Bayesian evidence.A forecast of the DESI survey shows that the dynamics of dark energy could be detected at the 7σ confidence level and would be decisively supported by Bayesian evidence,if the best-fit model of w derived from current data is the true model.  相似文献   

7.
We discuss a recent analysis by Yu et al.[RAA 11,125(2011)] about constraints on the smoothness parameter α and dark energy models using observational H(z) data.It is argued here that their procedure is conceptually inconsistent with the basic assumptions underlying the adopted Dyer-Roeder approach.In order to properly quantify the influence of the H(z) data on the smoothness parameter α,a χ2-test involving a sample of type Ia supernovae and H(z) data in the context of a flat ΛCDM model is reanalyzed.This r...  相似文献   

8.
In order to explore the properties of cosmic neutrinos, i.e. sum of the neutrino mass(∑m_ν) and the effective number of neutrino species(N_(eff)), which affects the Hubble expansion rate H(z)and the power of observational Hubble parameter data(OHD) in constraining cosmological parameters under the ΛCDM model, we utilize OHD to constrain the properties of cosmic neutrinos and apply an accurate H(z) function with mνand Neff. First, we simulate new OHD beyond the existing 43 OHD. According to the predictions of measurements of H_0(the current H(z) value), baryon acoustic oscillations(BAO) peaks, Sandage-Loeb(SL) test and cosmic microwave background(CMB), we assume observational accuracy up to 2% and redshift 0 z ≤5. With simulated H(z) data obtained from the fiducial model, we constrain the parameters including mνand Neff. When all parameters are set free, mν 0.196 eV(95%) and N_(eff)= 2.984 ± 0.826(68%) are obtained, and when fixing Neff as the standard baseline 3.046, we attain ∑m_ν 0.240 eV(95%). These constrained results are much tighter than the ones obtained by the current OHD, which makes the prospect of OHD in constraining cosmological parameters more promising as its accuracy and quantity grow.  相似文献   

9.
We consider spatially homogeneous and anisotropic Bianchi type V space- time with a bulk viscous fluid source, and time varying gravitational constant G and cosmological term Λ. The coefficient of bulk viscosity ζ is assumed to be a simple linear function of the Hubble parameter H (i.e. ζ = ζ 0 + ζ 1 H , where ζ 0 and ζ 1 are constants). The Einstein field equations are solved explicitly by using a law of variation for the Hubble parameter, which yields a constant value of the deceleration parameter. Physical and kinematical parameters of the models are discussed. The models are found to be compatible with the results of astronomical observations.  相似文献   

10.
The property of dark energy and the physical reason for the acceleration of the present universe are two of the most difficult problems in modern cosmology. The dark energy contributes about two-thirds of the critical density of the present universe from the observations of type-la supemovae (SNe Ia) and anisotropy of cosmic microwave background (CMB). The SN Ia observations also suggest that the universe expanded from a deceleration to an acceleration phase at some redshift, implying the existence of a nearly uniform component of dark energy with negative pressure. We use the "Gold" sample containing 157 SNe Ia and two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore the properties of dark energy and the transition redshift. For a flat universe with the cosmological constant, we measureΩM = 0.28-0.05 0.04, which is consistent with Riess et al. The transition redshift is ZT = 0.60-0.08 0.06. We also discuss several dark energy models that define w(z) of the parameterized equation of state of dark energy including one parameter and two parameters (w(z) being the ratio of the pressure to energy density). Our calculations show that the accurately calculated transition redshift varies from ZT = 0.29-0.06 0.07 to zT = 0.60-0.08 0.06 across these models. We also calculate the minimum redshift zc at which the current observations need the universe to accelerate.  相似文献   

11.
We show that a phenomenological form of energy density for the scalar field can provide the required transition from decelerated(q 0) to accelerated expansion(q 0) phase of the universe.We have used the latest type Ia supernova(SNIa) and Hubble parameter datasets to constrain the model parameters. The best fit values obtained from those datasets are then applied to reconstruct ωφ(z), the equation of state parameter for the scalar field. The results show that the reconstructed forms of q(z) and ω_φ(z) do not differ much from the standard ΛCDM value at the current epoch. Finally, the functional form of the relevant potential V(φ) is derived by a parametric reconstruction. The corresponding V(φ)comes out to be a double exponential potential, which has a number of cosmological implications.Additionally, we have also studied the effect of this particular scalar field dark energy sector on the evolution of matter overdensities.  相似文献   

12.
Hubble tension between the local measurement and global observation has been a key problem in cosmology. In this paper, we consider the quintessence scalar field, phantom field and quintom field as the dark energy to reconcile this problem. Different from most previous work, we start from the dimensionless equation of state(w) of dark energy, not a parameterization of potential. The combined analysis shows that observational data sets favor Hubble constant H0 =71.3-0.917  相似文献   

13.
We explore the problems of degeneracy and discreteness in the standard cosmological model(ΛCDM). We use the Observational Hubble Data(OHD) and the type Ia supernovae(SNe Ia) data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way of model differentiation when using different models to fit the observational data.  相似文献   

14.
Different measurements of the Hubble constant(H0)are not consistent,and a tension between the CMB based methods and cosmic distance ladder based methods has been observed.Measurements from various distance based methods are also inconsistent.To aggravate the problem,the same cosmological probe(TypeⅠa SNe for instance)calibrated through different methods also provides different values of H0.We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope(HST).Our analysis is based on parametric(t-test)as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test.Our results show that different methods provide different values of H0 and the differences are statistically significant.The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme.The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.  相似文献   

15.
Is it possible that the current cosmic accelerating expansion will turn into a decelerating one? Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmology? We study a class of phenomenological models with a transient acceleration,based on a dynamical dark energy with a very general form of equation of state pde= αρde- βρmde.It mimics the cosmological constant ρde→ const for a small scale factor a,and behaves as a barotropic gas with ρde→ a-3(α+1)with α≥ 0 for large a.The cosmic evolution of four models in the class has been examined in detail,and all yield a smooth transient acceleration.Depending on the specific model,the future universe may be dominated by either dark energy or by matter.In two models,the dynamical dark energy can be explicitly realized by a scalar field with an analytical potential V(φ).Moreover,a statistical analysis shows that the models can be as robust as ΛCDM in confronting the observational data of Type Ia supernovae,cosmic microwave background(CMB) and baryon acoustic oscillation.As improvements over previous studies,our models overcome the problem of over-abundance of dark energy during early eras,and satisfy the constraints on dark energy from WMAP observations of CMB.  相似文献   

16.
We propose an accurate test of the distance-duality (DD) relation, η = DL(z)(1 + z)-2/DA(z) = 1 (where DL and DA are the luminosity distances and angular diameter distances, respectively), with a combination of cosmological observational data of Type Ia Supernovae (SNe Ia) from the Union2 set and the galaxy cluster sample under an assumption of the spherical model. In order to avoid bias brought on by redshift non-coincidence between observational data and to consider redshift error bars of both clusters an...  相似文献   

17.
We present constraints on the quintessence scalar field model from observational data of the variation of the fine structure constant obtained from the Keck telescope and VLT. Within the theoretical frame proposed by Bekenstein, the constraints on the parameters of the quintessence scalar field model are obtained. Considering the prior of Ωm0 as WMAP 7 suggests, we obtain various results from different sam- ples. Based on these results, we also calculate the probability density function of the coupling constant ζ. The best-fit values show a consistent relationship between ζ and the different experimental results. In our work, we test two different potential models, namely, the inverse power law potential and the exponential potential. The results show that both the large value of the parameters in the potential and the strong coupling can cause a variation in the fine structure constant.  相似文献   

18.
The accelerated expansion of the Universe was proposed through the use of Type-Ia supernovae （SNe） as standard candles. The standardization depends on an empirical correlation between the stretch/color and peak luminosity of the light curves. The use of Type-Ia SNe as standard candles rests on the assumption that their properties （and this correlation） do not vary with redshift. We consider the possibility that the majority of Type-Ia SNe are in fact caused by a Quark-Nova detonation in a tight neutron-star-CO-white-dwarf binary system, which forms a Quark-Nova Ia （QN-Ia）. The spin-down energy injected by the Quark-Nova remnant （the quark star） contributes to the post-peak light curve and neatly explains the observed correlation between peak luminosity and light curve shape. We demonstrate that the parameters describing QN-Ia are NOT constant in redshift. Simulated QN-Ia light curves provide a test of the stretch/color correlation by comparing the true distance modulus with that determined using SN light curve fitters. We determine a correction between the true and fitted distance moduli, which when applied to Type-Ia SNe in the Hubble diagram recovers the ΩM = 1 cosmology. We conclude that Type-Ia SNe observations do not necessitate the need for an accelerating expansion of the Universe （if the observed SNe Ia are dominated by QNe Ia） and by association the need for dark energy.  相似文献   

19.
We study cosmic dynamics in the context of the normal branch of the DGP braneworld model.Using current Planck data, we find the best fitting model and associated cosmological parameters in non-flat ΛDGP. With the transition redshift as a basic variable and statefinder parameters, our result shows that the Universe starts its accelerated expansion phase slightly earlier than expected in ΛCDM cosmology. The result also alleviates the coincidence problem of the ΛCDM model.  相似文献   

20.
Ultra-light axions(ULAs) with mass less than 10-20 eV have interesting behaviors that may contribute to either dark energy or dark matter at different epochs of the Universe. Their properties can be explored by cosmological observations, such as expansion history of the Universe, cosmic large-scale structure, cosmic microwave background, etc. In this work, we study the ULAs with mass around 10~(-33) eV,which means that the ULA field still rolls slowly at present with the equation of state w =-1 as dark energy. To investigate the mass and other properties of this kind of ULA field, we adopt the measurements of Type Ia supernova(SN Ia), baryon acoustic oscillation(BAO), and Hubble parameter H(z). The Markov Chain Monte Carlo(MCMC) technique is employed to perform the constraints on the parameters. Finally,by exploring four cases of the model, we find that the mass of this ULA field is about 3 × 10-33 eV if assuming the initial axion field φ_i = M_(pl). We also investigate a general case by assuming φ_i ≤ M_(pl), and find that the fitting results of φ_i/M_(pl) are consistent with or close to 1 for the datasets that we use.  相似文献   

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