We study modified Chaplygin gas (MCG) as a candidate for dark energy and predict the values of parameters of the gas for a physically viable cosmological model. The equation of state of MCG involves three parameters: B, A and α. The permitted values of these parameters are determined with the help of a dimensionless age parameter (H0t0) and H(z) −z data. Specifically, we study the allowed ranges of values of the B parameter in terms of α and As (As is defined in terms of the parameters in the theory). We explore the constraints of the parameters in the cold dark matter and unified dark matter energy models, respectively.

A specific class of flat Emergent Universe (EU) is considered and its viability is tested in view of the recent observations. Model parameters are constrained from Stern data for Hubble parameter and redshift [H(z) versus z] and from a model-independent measurement of BAO peak parameter. It is noted that a composition of exotic matter, dust and dark energy, capable of producing an EU, cannot be ruled out with present data. Evolution of other relevant cosmological parameters, viz. density parameter ( ) and effective equation of state (EOS) parameter (ω eff ), are also shown.

We study a composition of normal and exotic matter which is required for a flat emergent universe scenario permitted by the equation of state (EOS) (p=Aρ−Bρ1/2) and predict the range of the permissible values for the parameters A and B to explore a physically viable cosmological model. The permitted values of the parameters are determined taking into account the H(z)−z data obtained from observations, a model‐independent Baryon Acoustic Oscillation (BAO) peak parameter and cosmic microwave background shift parameter (WMAP7 data). It is found that although A can be very close to zero, most of the observations favours a small and negative A. As a consequence, the effective EOS parameter for this class of emergent universe solutions remains negative always. We also compared the magnitude [μ (z)] versus redshift (z) curve obtained in the model with that obtained from the union compilation data. According to our analysis the class of emergent universe solutions considered here is not ruled out by the observations.

Abstract. We investigate the linear growth function for the large scale structures of the universe considering modified Chaplygin gas as dark energy. Taking into account observational growth data for a given range of redshift from the Wiggle-Z measurements and rms mass fluctuations from Ly-α measurements we numerically analyze cosmological models to constrain the parameters of the MCG. The observational data of Hubble parameter with redshift (Z) is also considered. The Wang-Steinhardt ansatz for growth index γ and growth function f (defined as f = Ω γ m (a)) are considered for the numerical analysis. The best-fit values of the equation of state parameters obtained here is employed to study the growth function (f ), growth index (γ) and state parameter (ω) with redshift z. We note that MCG satisfactorily accommodates an accelerating phase followed by a matter dominated universe.

We study cosmological models with modified Chaplygin gas (in short, MCG) to determine observational constraints on its EoS parameters. The observational data of the background and the growth tests are employed. The background test data namely, H(z) − z data, CMB shift parameter, Baryonic acoustic oscillations (BAO) peak parameter, SN Ia data are considered to study the dynamical aspects of the universe. The growth test data we employ here consists of the linear growth function for the large scale structures of the universe, models are explored assuming MCG as a candidate for dark energy. Considering the observational growth data for a given range of redshift from the Wiggle-Z measurements and rms mass fluctuations from Ly-α measurements, cosmological models are analyzed numerically to determine constraints on the MCG parameters. In this case, the Wang-Steinhardt ansatz for the growth index γ and growth function f (defined as f = Ω γ m (a)) are also taken into account for the numerical analysis. The best-fit values of the equation of state parameters obtained here are used to study the variation of the growth function (f ), growth index (γ), equation of state parameter (ω), squared sound speed c 2 s and deceleration parameter with redshift z. The observational constraints on the MCG parameters obtained here are then compared with those of the GCG model for viable cosmology. It is noted that MCG models satisfactorily accommodate an accelerating phase followed by a matter dominated phase of the universe. The permitted range of values of the EoS parameters and the associated parameters (f , γ, ω, Ω, c 2 s , q) are compared with those obtained earlier using other observations.

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A class of emergent universe models is studied in the light of recent observational data. Significant constraints on model parameters are obtained from these observations. The density parameter for a class of models is also evaluated. Some of the models are in accordance with recent observations. Others are not of interest, yielding unrealistic present‐day values of the density parameter.

We present Cosmological models with modified Chaplygin gas (MCG) in the framework of Horava-Lifshitz (HL) theory of gravity both with and without detailed balance. The equation of state (EOS) for a MCG contains three unknown parameters namely, A, α, B. The allowed values of some of these parameters of the EOS are determined using the recent astrophysical and cosmological observational data. Using observational data from H(z) − z, BAO peak parameter, CMB shift parameter we study cosmologies in detailed-balance and beyond detailed-balance scenario. In this paper we take up the beyond detailed-balance scenario in totality and contribution of dark radiation in the case of detailed-balance scenario on the parameters of the EOS. We explore the effect of dark radiation on the whole range the of effective neutrino parameter to constrain matter contributing parameter B in both the detailed-balance and the beyond-detailed balance scenario. It has been observed that greater the dark radiation less the matter contribution in the MCG in both the scenario considered here. In order to check the validity of beyond detailed balance scenario we plot supernovae magnitudes (µ) with redshift of Union2 data and then the variation of state parameter with redshift is studied. It has been observed that beyond detailed balance scenario is equally suitable in HL gravity with MCG.