scholarly journals Friedmann cosmology with decaying vacuum density in Brans–Dicke theory

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
C. P. Singh ◽  
Joan Solà Peracaula
Keyword(s):  
Equation Of State ◽  
Hubble Parameter ◽  
Hubble Constant ◽  
Flat Space ◽  
Acoustic Oscillation ◽  
Vacuum Energy Density ◽  
Exact Nature ◽  
Time Varying ◽  
Type Ia ◽  
Sigma H

AbstractIn this paper, we study Friedmann cosmology with time-varying vacuum energy density in the context of Brans–Dicke theory. We consider an isotropic and homogeneous flat space, filled with a matter-dominated perfect fluid and a dynamical cosmological term $$\varLambda (t) $$ Λ ( t ) , obeying the equation of state of the vacuum. As the exact nature of a possible time-varying vacuum is yet to be found, we explore $$\varLambda (t)$$ Λ ( t ) given by the phenomenological law $$\varLambda (t)=\lambda +\sigma H$$ Λ ( t ) = λ + σ H , where $$\lambda $$ λ and $$\sigma $$ σ are positive constants. We solve the model and then focus on two different cases $$\varLambda _{H1}$$ Λ H 1 and $$\varLambda _{H2}$$ Λ H 2 by assuming $$\varLambda =\lambda $$ Λ = λ and $$\varLambda =\sigma H$$ Λ = σ H , respectively. Notice that $$\varLambda _{H1}$$ Λ H 1 is the analog of the standard $$\varLambda $$ Λ CDM, but within the Brans–Dicke cosmology. We find the analytical solution of the main cosmological functions such as the Hubble parameter, the scale factor, deceleration and equation of state parameters for these models. In order to test the viability of the cosmological scenarios, we perform two sets of joint observational analyses of the recent Type Ia supernova data (Pantheon), observational measurements of Hubble parameter data, Baryon acoustic oscillation/Cosmic microwave background data and Local Hubble constant for each model. For the sake of comparison, the same data analysis is performed for the $$\varLambda $$ Λ CDM model. Each model shows a transition from decelerated phase to accelerated phase and can be viewed as an effective quintessence behavior. Using the model selection criteria AIC and BIC to distinguish from existing dark energy models, we find that the Brans–Dicke analog of the $$\varLambda $$ Λ -cosmology (i.e. our model $$\varLambda _{H1}$$ Λ H 1 ) performs at a level comparable to the standard $$\varLambda $$ Λ CDM, whereas $$\varLambda _{H2}$$ Λ H 2 is less favoured.

CPL effective dark energy from the backreaction effect

2019 ◽  
Vol 34 (21) ◽  
pp. 1950167
Author(s):  
Yan-Hong Yao ◽  
Xin-He Meng
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Perfect Fluid ◽  
Coming Out ◽  
Hubble Parameter ◽  
Small Scale ◽  
Type Ia Supernova ◽  
Type Ia ◽  
The Difference ◽  
The Universe

In this paper, we interpret the dark energy as an effect caused by small-scale inhomogeneities of the universe with the use of the spatial averaged approach of Buchert [Gen. Relat. Gravit. 32, 105 (2000); 33, 1381 (2001)]. The model considered here adopts the Chevallier–Polarski–Linder (CPL) parametrizations of the equation of state of the effective perfect fluid from the backreaction effect. Thanks to the effective geometry introduced by Larena et al. [Phys. Rev. D 79, 083011 (2009)] in their previous work, we confront such backreaction model with the latest type Ia supernova and Hubble parameter observations, coming out with the results that reveal the difference between the Friedmann–Lemaître–Robertson–Walker model and backreaction model.

Test of the cosmic transparency with the standard candles and the standard ruler

2018 ◽  
Vol 27 (05) ◽  
pp. 1850054 ◽  
Author(s):  
Jun Chen
Keyword(s):  
Observational Data ◽  
Confidence Level ◽  
Free Parameter ◽  
Hubble Constant ◽  
Systematic Errors ◽  
Acoustic Oscillation ◽  
Independent Method ◽  
Baryon Acoustic Oscillation ◽  
Type Ia ◽  
Model Independent

In this paper, the cosmic transparency is constrained by using the latest baryon acoustic oscillation (BAO) data and the type Ia supernova data with a model-independent method. We find that a transparent universe is consistent with observational data at the [Formula: see text] confidence level, except for the case of BAO+ Union 2.1 without the systematic errors where a transparent universe is favored only at the [Formula: see text] confidence level. To investigate the effect of the uncertainty of the Hubble constant on the test of the cosmic opacity, we assume [Formula: see text] to be a free parameter and obtain that the observations favor a transparent universe at the [Formula: see text] confidence level.

Brane cosmological constant in two-brane warped geometry model

2014 ◽  
Vol 29 (20) ◽  
pp. 1450093
Author(s):  
Sayantani Lahiri ◽  
Soumitra SenGupta
Keyword(s):  
Cosmological Constant ◽  
Hubble Parameter ◽  
Vacuum Energy ◽  
Hubble Constant ◽  
Time Dependent ◽  
Time Varying ◽  
Constant Modulus ◽  
Expanding Universe ◽  
Geometry Model ◽  
The Universe

In the backdrop of generalized Randall–Sundrum braneworld scenario, we look for the possible origin of an effective four-dimensional cosmological constant (Ω vis ) on the visible three-brane due to the effects of bulk curvature and the modulus field that can either be a constant or a time-dependent quantity. In case of constant modulus field, the induced Ω vis leads to an exponentially expanding universe and the presence of vacuum energy densities on either of the three-branes as well as a nonvanishing bulk curvature [Formula: see text] are essential to generate an effective Ω vis . The Hubble constant turns out to be equal to the visible brane cosmological constant which agrees with the present result. In an alternative scenario, a time-dependent modulus field is found to be capable of decelerating the universe. The Hubble parameter, in this case is determined for a slowly time-varying modulus field.

scholarly journals Probing cosmic opacity with the type Ia supernovae and Hubble parameter

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Bing Xu ◽  
Kaituo Zhang ◽  
Qihong Huang
Keyword(s):  
Hubble Parameter ◽  
Likelihood Function ◽  
Nuisance Parameter ◽  
Hubble Constant ◽  
Absolute Magnitude ◽  
Type Ia Supernovae ◽  
Spatial Curvature ◽  
Type Ia ◽  
Ia Supernovae ◽  
Best Fit

AbstractIn this paper, we probe the cosmic opacity with the newest Pantheon type Ia supernovae (SNIa) and the observational Hubble parameter $$\left( H(z)\right) $$ H ( z ) data based on the $$\Lambda $$ Λ CDM and wCDM models with or without spatial curvature. In the analysis, we marginalize the likelihood function of SNIa data over the pertinent nuisance parameter $${\mathcal {M}}$$ M , a combination of the absolute magnitude of SNIa $$M_{\mathrm{B}}$$ M B and the Hubble constant $$H_0$$ H 0 , with a flat prior. Two parameterizations of the optical depth $$\tau (z)$$ τ ( z ) associated to the cosmic absorption, namely $$\tau (z)=2\varepsilon z$$ τ ( z ) = 2 ε z and $$\tau (z)= (1+z)^{2\varepsilon }-1$$ τ ( z ) = ( 1 + z ) 2 ε - 1 , are adopted. We find that the results are not sensitive to the fiducial cosmological models, the spatial curvature and parameterizations of $$\tau (z)$$ τ ( z ) . Moreover, the results from the Pantheon data alone are consistent with a transparent universe ($$\varepsilon =0$$ ε = 0 ). And once the H(z) data is combined, $$\varepsilon =0$$ ε = 0 falls within the 68% confidence level (CL) of the best fit when a flat $$H_0$$ H 0 prior or the distance priors are used, while it falls within the 95% CL when a Gaussian distribution prior of $$H_0=74.03\pm 1.42$$ H 0 = 74.03 ± 1.42 km $$\mathrm {s}^{-1}\, \mathrm {Mpc}^{-1}$$ s - 1 Mpc - 1 is used.

Cosmological implications of the dark matter equation of state

2017 ◽  
Vol 26 (03) ◽  
pp. 1750013 ◽  
Author(s):  
Weiqiang Yang ◽  
Hang Li ◽  
Yabo Wu ◽  
Jianbo Lu
Keyword(s):  
Dark Matter ◽  
Equation Of State ◽  
Cold Dark Matter ◽  
Evolution Equations ◽  
State Parameter ◽  
Acoustic Oscillation ◽  
Text Data ◽  
Equation Of State Parameter ◽  
Type Ia ◽  
Ia Supernovae

In this paper, we study a model which is composed of the cosmological constant and dark matter with nonzero equation of state parameter, which could be called as [Formula: see text]wDM. In the synchronous gauge, we obtain the perturbation equations of dark matter, and deduce the evolution equations of growth factor about the dark matter and baryons. Based on the Markov Chain Monte Carlo (MCMC) method, we constrain this model by the recently available cosmic observations which include cosmic microwave background (CMB) radiation, baryon acoustic oscillation (BAO), type Ia supernovae (SNIa) and [Formula: see text] data points from redshift-space distortion (RSD). The results present a tighter constraint on the model than the case without [Formula: see text] data. In 3[Formula: see text] regions, we find the dark matter equation of state parameter [Formula: see text]. The currently available cosmic observations do not favor the nonzero dark matter equation of state parameter, no deviation from the lambda cold dark matter ([Formula: see text]CDM) model is found in 1[Formula: see text] region.

scholarly journals Baryon acoustic oscillation, Hubble parameter, and angular size measurement constraints on the Hubble constant, dark energy dynamics, and spatial curvature

2019 ◽  
Vol 488 (3) ◽  
pp. 3844-3856 ◽  
Author(s):  
Joseph Ryan ◽  
Yun Chen ◽  
Bharat Ratra
Keyword(s):  
Dark Energy ◽  
Hubble Parameter ◽  
Angular Size ◽  
Hubble Constant ◽  
Acoustic Oscillation ◽  
Baryon Acoustic Oscillation ◽  
Size Measurement ◽  
Data Combination ◽  
Energy Dynamics ◽  
Constant Dark

ABSTRACT In this paper, we use all available baryon acoustic oscillation, Hubble parameter, and quasar angular size data to constrain six dark energy cosmological models, both spatially flat and non-flat. Depending on the model and data combination considered, these data mildly favour closed spatial hypersurfaces (by as much as 1.7σ) and dark energy dynamics (up to a little over 2σ) over a cosmological constant Λ. The data also favour, at 1.8σ to 3.4σ, depending on the model and data combination, a lower Hubble constant than what is measured from the local expansion rate.

scholarly journals Cosmological models, observational data and tension in Hubble constant

2020 ◽  
pp. 1-20
Author(s):  
G.S. Sharov ◽  
E.S. Sinyakov
Keyword(s):  
Observational Data ◽  
Hubble Parameter ◽  
Background Radiation ◽  
Hubble Constant ◽  
Cosmological Models ◽  
Model Parameters ◽  
Data Sets ◽  
Type Ia ◽  
Data Points ◽  
Ia Supernovae

We analyze how predictions of cosmological models depend on a choice of described observational data, restrictions on flatness, and how this choice can alleviate the H tension. These effects are demonstrated in the wCDM model in comparison with the standard ΛCDM model. We describe the Pantheon sample observations of Type Ia supernovae, 31 Hubble parameter data points H(z) from cosmic chronometers, the extended sample with 57 H(z) data points and observational manifestations of cosmic microwave background radiation (CMB). For the wCDM and ΛCDM models in the flat case and with spatial curvature, we calculate χfunctions for all observed data in different combinations, estimate optimal values of model parameters and their expected intervals. For both considered models the results essentially depend on a choice of data sets. In particular, for the wCDM model with H(z) data, supernovae and CMB the 1σ estimations may vary from H = 67.52km /(s·Mpc) (for all N = 57 Hubble parameter data points) up to H = 70.87 /(s·Mpc) for the flat case (k = 0) and N = 31. These results might be a hint how to alleviate the problem of H tension: different estimates of the Hubble constant may be connected with filters and a choice of observational data.

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