Showing papers on "Deceleration parameter published in 2016"

Constraining the cosmic deceleration-acceleration transition with type Ia supernova, BAO/CMB and H(z) data

Abstract: We revisit the kink-like parametrization of the deceleration parameter (q(z)) [1], which considers a transition, at redshift zt, from cosmic deceleration to acceleration. In this parametrization the initial (z zt) value of the q-parameter is qi, its nal ( z = 1) value is qf and the duration of the transition is parametrized by . We obtain constraints on the free parameters of the model using recent data from type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO), cosmic microwave background (CMB) and the Hubble parameter (H(z)). The use of H(z) data introduces an explicit dependence of the combined likelihood on the present value of the Hubble parameter (H0), allowing us to explore the inuence of dierent priors when marginalizing over this parameter. We also study the importance of the CMB information in the results by considering data from WMAP7, WMAP9 (Wilkinson Microwave Anisotropy Probe - 7 and 9 years) and the Planck satellite. Assuming a at space geometry, qi = 1=2 and expressing the present value of the deceleration parameter (q0) as a function of the others three free parameters, we obtain zt = 0:68 +0:10

Kaluza–Klein cosmological model in f ( R , T ) gravity with Λ( T )

Abstract: A class of Kaluza–Klein cosmological models in f(R, T) theory of gravity have been investigated. In the work, we have considered the functional f(R, T) to be in the form $$f(R,T)=f(R)+f(T)$$ with $$f(R)=\lambda R$$ and $$f(T)=\lambda T$$ . Such a choice of the functional f(R, T) leads to an evolving effective cosmological constant $$\Lambda $$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads to two different aspects of the volumetric expansion, namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair, we have found that the model with exponential volumetric expansion behaves more like a lambda cold dark matter model.

A transition from a decelerated to an accelerated phase of the universe expansion from the simplest non-trivial polynomial function of T in the f(R,T) formalism

Abstract: In this work we present cosmological solutions from the simplest non-trivial polynomial function of \(T\) in \(f(R,T)\) theory of gravity, with \(R\) and \(T\) standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Although such an approach yields a highly non-linear differential equation for the scale factor, we show that it is possible to obtain analytical solutions for the cosmological parameters. For some values of the free parameters, the model is able to predict a transition from a decelerated to an accelerated expansion of the universe and the values of the deceleration parameter agree with observation.

A divergence-free parametrization of deceleration parameter for scalar field dark energy

Abstract: In this paper, we have considered a spatially flat FRW universe filled with pressureless matter and dark energy (DE). We have considered a phenomenological parametrization of the deceleration parameter q(z) and from this, we have reconstructed the equation-of-state (EoS) for DE ωϕ(z). This divergence-free parametrization of the deceleration parameter is inspired from one of the most popular parametrization of the DE EoS given by Barboza and Alcaniz [see E. M. Barboza and J. S. Alcaniz, Phys. Lett. B 666 (2008) 415]. Using the combination of datasets (Type Ia Supernova (SN Ia) + Hubble + baryonic acoustic oscillations/cosmic microwave background (BAO/CMB)), we have constrained the transition redshift zt (at which the universe switches from a decelerating to an accelerating phase) and have found the best fit value of zt. We have also compared the reconstructed results of q(z) and ωϕ(z) and have found that the results are compatible with a ΛCDM universe if we consider SN Ia + Hubble data, but inclusion of BAO/CMB data makes q(z) and ωϕ(z) incompatible with ΛCDM model. The potential term for the present toy model is found to be functionally similar to a Higgs potential.

Parametric reconstruction of the cosmological jerk from diverse observational data sets

Abstract: A parametric reconstruction of the jerk parameter, the third order derivative of the scale factor expressed in a dimensionless way, has been discussed. Observational constraints on the model parameters have been obtained by maximum likelihood analysis of the models using supernova distance modulus data, observational Hubble data, baryon acoustic oscillation data, and cosmic microwave background shift parameter data. The present value of the jerk parameter has been kept open to start with, but the plots of various cosmological parameters, like deceleration parameter $q(z)$, jerk parameter $j(z)$, and dark energy equation of state parameter ${w}_{\mathrm{DE}}(z)$ indicate that the reconstructed models are very close to a $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model with a slight inclination toward a nonphantom behavior of the evolution.

Some Bianchi type generalized ghost piligrim dark energy models in general relativity

Abstract: In this paper, we consider Bianchi type- $\mathit{III}$ , $V$ and $\mathit{VI}_{0}$ space-times filled with generalized ghost pilgrim dark energy (GGPDE) in general relativity. Here we assume the anisotropic distribution of GGPDE by introducing skewness parameters. To get deterministic solutions, we consider the scale factor $a(t)=(t^{n}e^{t})^{ \frac{1}{k}}$ , so called hybrid expansion, which yields a time dependent deceleration parameter, and exhibits a transition of the Universe from early decelerated phase to the recent accelerating phase. To describe the behavior of the obtained models we construct equation of state ( $\omega_{\varLambda }$ ), squared sound speed ( $v_{s}^{2}$ ) parameters and $\omega_{\varLambda }$ – $\dot{\omega }_{\varLambda }$ , $r$ – $s$ planes. It is worth mentioning here that the analysis of evolution parameters supports the concept of pilgrim dark energy (PDE). Also, these models remain stable for PDE parameter $\beta =-0.5$ . Moreover, the cosmological planes correspond to $\varLambda \mathit{CDM}$ limit as well as different well-known dark energy models.

Bianchi type string cosmological models in f(R,T) gravity

Abstract: In this work we have studied Bianchi-III and - VI 0 cosmological models with string fluid source in f(R,T) gravity (T. Harko et al., Phys. Rev. D 84, 024020 (2011)), where R is the Ricci scalar and T the trace of the stress energy-momentum tensor in the context of late time accelerating expansion of the universe as suggested by the present observations. The exact solutions of the field equations are obtained by using a time-varying deceleration parameter. The universe is anisotropic and free from initial singularity. Our model initially shows acceleration for a certain period of time and then decelerates consequently. Several dynamical and physical behaviors of the model are also discussed in detail.

Dynamics of Bianchi type I, III and Kantowski-Sachs solutions in f(R,T) gravity

Abstract: In this paper, we reconstruct a suitable model in $f(R,T)$ gravity, (where $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor) which depict the current cosmic picture in more consistent way. The dynamical field equations are solved for generic anisotropic space-time. The solution of field equations helps us to determine the future cosmic evolution for both physical and kinematical quantities. We explore the nature of deceleration parameter, NEC and energy density for three different cases representing Bianchi type I, III and Kantowski-Sachs universe model. We find that this study favors the phantom cosmic evolution in all cases.

A transitioning universe with anisotropic dark energy

Abstract: In this paper, we present a model of transitioning universe with minimal interaction between perfect fluid and anisotropic dark energy in Bianchi I space-time. The two sources are assumed to minimally interacted and therefore their energy momentum tensors are conserved separately. The explicit expression for average scale factor are considered in hybrid form that gives time varying deceleration parameter which describes both the early and late time physical features of universe. We also discuss the physical and geometrical properties of the model derived in this paper. The solution is interesting physically as it explain accelerating universe as well as singularity free universe.

Anisotropic universe with magnetized dark energy

Abstract: In the present work we have searched the existence of the late time acceleration of the Universe filled with cosmic fluid and uniform magnetic field as source of matter in anisotropic Heckmann-Schucking space-time. The observed acceleration of universe has been explained by introducing a positive cosmological constant $\varLambda$ in the Einstein’s field equation which is mathematically equivalent to vacuum energy with equation of state (EOS) parameter set equal to −1. The present values of the matter and the dark energy parameters $(\varOmega_{m})_{0}$ & $(\varOmega_{\varLambda})_{0}$ are estimated in view of the latest 287 high red shift ( $0.3 \leq z \leq1.4$ ) SN Ia supernova data’s of observed apparent magnitude along with their possible error taken from Union 2.1 compilation. It is found that the best fit value for $(\varOmega_{m})_{0}$ & $(\varOmega_{\varLambda})_{0}$ are 0.2820 & 0.7177 respectively which are in good agreement with recent astrophysical observations in the latest surveys like WMAP [2001–2013], Planck [latest 2015] & BOSS. Various physical parameters such as the matter and dark energy densities, the present age of the universe and deceleration parameter have been obtained on the basis of the values of $(\varOmega_{m})_{0}$ & $(\varOmega_{\varLambda})_{0}$ . Also we have estimated that the acceleration would have begun in the past at $z = 0.71131 \thicksim6.2334~\mbox{Gyrs}$ before from present.

Dark Energy Models in f(R, T) Theory with Variable Deceleration Parameter

Abstract: In this communication we have investigated Bianchi type-II dark energy (DE) cosmological models with and without presence of magnetic field in modified f(R, T) gravity theory as proposed by Harko et al. (Phys. Rev. D, 84, 024020, 2011). The exact solution of the field equations is obtained by setting the deceleration parameter q as a time function along with suitable assumption the scale factor $a(t)= [sinh(\alpha t)]^{\frac {1}{n}}$ , α and n are positive constant. We have obtained a class of accelerating and decelerating DE cosmological models for different values of n and α. The present study believes that the mysterious dark energy is the main responsible force for accelerating expansion of the universe. For our constructed models the DE candidates cosmological constant (Λ) and the EoS parameter (ω) both are found to be time varying quantities. The cosmological constant Λ is very large at early time and approaches to a small positive value at late time whereas the EoS parameters is found small negative at present time. Physical and kinematical properties of the models are discussed with the help of pictorial representations of the parameters. We have observed that our constructed models are compatible with recent cosmological observations.

Cosmic acceleration from matter–curvature coupling

Abstract: We consider $$f\left( {R,T} \right) $$ modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy–momentum tensor. We indicate that in this type of the theory, the coupling energy–momentum tensor is not conserved. However, we mainly focus on a particular model that matter is minimally coupled to the geometry in the metric formalism and wherein, its coupling energy–momentum tensor is also conserved. We obtain the corresponding Raychaudhuri dynamical equation that presents the evolution of the kinematic quantities. Then for the chosen model, we derive the behavior of the deceleration parameter, and show that the coupling term can lead to an acceleration phase after the matter dominated phase. On the other hand, the curvature of the universe corresponds with the deviation from parallelism in the geodesic motion. Thus, we also scrutinize the motion of the free test particles on their geodesics, and derive the geodesic deviation equation in this modified theory to study the accelerating universe within the spatially flat FLRW background. Actually, this equation gives the relative accelerations of adjacent particles as a measurable physical quantity, and provides an elegant tool to investigate the timelike and the null structures of spacetime geometries. Then, through the null deviation vector, we find the observer area–distance as a function of the redshift for the chosen model, and compare the results with the corresponding results obtained in the literature.

A comprehensive investigation on the slowing down of cosmic acceleration

Abstract: Shafieloo ea al. firstly proposed the possibility that the current cosmic acceleration (CA) is slowing down. However, this is rather counterintuitive because a slowing down CA cannot be accommodated in most mainstream cosmological models. In this work, by exploring the evolutionary trajectories of dark energy equation of state w(z) and deceleration parameter q(z), we present a comprehensive investigation on the slowing down of CA from both the theoretical and the observational sides. For the theoretical side, we study the impact of different w(z) by using six parametrization models, and then discuss the effects of spatial curvature. For the observational side, we investigate the effects of different type Ia supernovae (SNe Ia), different baryon acoustic oscillation (BAO), and different cosmic microwave background (CMB) data, respectively. We find that (1) The evolution of CA are insensitive to the specific form of w(z); in contrast, a non-flat Universe more favors a slowing down CA than a flat Universe. (2) SNLS3 SNe Ia datasets favor a slowing down CA at 1 confidence level, while JLA SNe Ia samples prefer an eternal CA; in contrast, the effects of different BAO data are negligible. (3) Compared with CMB distance prior data, full CMB data more favor a slowing down CA. (4) Due to the low significance, the slowing down of CA is still a theoretical possibility that cannot be confirmed by the current observations. Subject headings: Cosmology: dark energy, observations, cosmological parameters

Phenomenological Varying Modified Chaplygin Gas with Variable G and Λ: Toy Models for Our Universe

Abstract: In this paper, we have considered varying modified Chaplygin gas in case of variable G and Λ. Since varying G and Λ give rises to modified form of field equations and conservation law, we have considered two different toy models. In the first model, the Universe is filled with a phenomenological gas while in the second one, there is the existence of gas and a matter with P = ω(t)ρ m . By considering sign changeable interaction between fluids we have analyzed important cosmological parameters such as EoS parameter of the fluids and deceleration parameter q of the models.

Constraints on reconstructed dark energy model from SN Ia and BAO/CMB observations

Abstract: The motivation of the present work is to reconstruct a dark energy model through the {\it dimensionless dark energy function} $X(z)$, which is the dark energy density in units of its present value. In this paper, we have shown that a scalar field $\phi$ having a phenomenologically chosen $X(z)$ can give rise to a transition from a decelerated to an accelerated phase of expansion for the universe. We have examined the possibility of constraining various cosmological parameters (such as the deceleration parameter and the effective equation of state parameter) by comparing our theoretical model with the latest Type Ia Supernova (SN Ia), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) radiation observations. Using the joint analysis of the SN Ia+BAO/CMB dataset, we have also reconstructed the scalar potential from the parametrized $X(z)$. The relevant potential is found, which comes to be a polynomial in $\phi$. From our analysis, it has been found that the present model favors the standard $\Lambda$CDM model within $1\sigma$ confidence level.

FRW cosmological models in Brans-Dicke theory of gravity with variable $q$ and dynamical $\varLambda$ -term

Abstract: Exact solution of modified Einstein’s field equations are considered within the scope of spatially homogeneous and isotropic Fraidmann-Robertson-Walker (FRW) space-time filled with perfect fluid in the frame work of Brans-Dicke scalar-tensor theory of gravity. In this paper we have investigated the flat, open and closed FRW models and the effect of dynamic cosmological term on the evolution of the universe. Two types of FRW cosmological models are obtained by setting the power law between the scalar field $\phi$ and the scale factor $a$ and deceleration parameter (DP) $q$ as a time dependent. The concept of time dependent DP with some proper assumptions yield two type of the average scale factors (i) $a(t)=[\sinh(\alpha t)]^{\frac{1}{n}}$ and (ii) $a(t)=[t^{\alpha}e^{t}]^{\frac{1}{n}}$ , $\alpha$ and $n eq 0$ are arbitrary constants. In case (i), for $0 < n \leq 1$ , it generates a class of accelerating models while for $n > 1$ , the models of the universe exhibit phase transition from early decelerating to present accelerating phase and the transition redshift $z_{t}$ has been calculated and found to be in good agreement with the results from recent astrophysical observations. In case (ii), for $n \geq 2$ and $\alpha = 1$ , we obtain a class of transit models of the universe from early decelerating to present accelerating phase. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time. The physical and geometric properties of the models are also discussed with the help of graphical presentations.

Cosmological models with linearly varying deceleration parameter in f(R,T) gravity

Abstract: In this paper, we investigate Friedmann-Robertson-Walker (FRW) cosmological model in the presence of perfect fluid source in \(f(R,T)\) gravity. We have used linearly varying deceleration parameter proposed by Akarsu and Dereli (Int. J. Theor. Phys. 51:612, 2012) and barotropic equation of state to obtain determinate solution of the field equations of the theory. Physical parameters of the model are determined and some physical and kinematical properties of the model are also discussed.

Anisotropic cosmologies with ghost dark energy models in f (R, T) gravity

Abstract: In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. For this purpose, we use the squared sound speed $ v_{s}^{2}$ whose sign determines the stability of the model. At first, the non-interacting ghost dark energy in a Bianchi type-I (BI) background is discussed. Then the equation-of-state parameter, $ \omega_D=p_{D}/\rho_{D}$ , the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It is shown that the equation-of-state parameter of the ghost dark energy can cross the phantom line ( $ \omega=-1$ in some range of the parameter spaces. Then, this investigation was extended to the general scheme for modified $ f(R,T)$ gravity reconstruction from a realistic case in an anisotropic Bianchi type-I cosmology, using the dark matter and ghost dark energy. Special attention is taken into account for the case in which the function f is given by $ f(R,T)=f_{1}(R) +f_{2}(T)$ . We consider a specific model which permits the standard continuity equation in this modified theory. Besides $ \Omega_{\Lambda}$ and $ \Omega$ in standard Einstein cosmology, another density parameter, $ \Omega_{\sigma}$ , is expected by the anisotropy. This theory implies that if $ \Omega_{\sigma}$ is zero then it yields the FRW universe model. Interestingly enough, we find that the corresponding f (R, T) gravity of the ghost DE model can behave like phantom or quintessence of the selected models which describe the accelerated expansion of the universe.

The general class of Bianchi cosmological models in f(R, T) gravity with dark energy in viscous cosmology

Abstract: The general class of Bianchi cosmological models in f(R, T) gravity with dark energy in the form of standard and modified Chaplygin gas and bulk viscosity have been considered. We have discussed three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The model describes an accelerating universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

Bianchi type I and V solutions in f(R, T) gravity with time-dependent deceleration parameter

Abstract: In this paper, our attention is to reconstruct an appropriate model for Bianchi type I and Bianchi V space–times in f(R, T) gravity with the help of special law of deceleration parameter in connection to f(R, T) gravity (where R is the Ricci scalar and T is the trace of energy–momentum tensor). We solve the modified Einstein field equations for anisotropic and homogeneous Bianchi type V space–time. The solution of field equations facilitates finding out the physical as well as kinematical quantities. We explore the behavior of null energy condition, energy density, and deceleration parameter to present cosmic picture.

Bianchi type- II $\mathit{II}$ , VIII $\mathit{VIII}$ and IX $\mathit{IX}$ cosmological models in a modified theory of gravity with variable Λ $\varLambda$

Abstract: Spatially homogeneous Bianchi type- $\mathit{II}$ , $\mathit{VIII}$ and $\mathit{IX}$ perfect fluid cosmological models in $f(R,T)$ modified theory of gravity have been investigated for a special choice of $f(R,T)=f_{1}(R)+f_{2}(T)$ with $f_{1}(R)=\lambda_{1}R$ and $f_{2}(T)=\lambda_{2}T$ . This special choice leads to a cosmological constant $\varLambda$ , which depends on stress energy tensor of matter source. To get the deterministic model of Universe, we assume that the expansion scalar ( $\theta$ ) in the model is proportional to shear scalar ( $\sigma$ ). This condition leads to relation between metric potentials, which yields a time dependent deceleration parameter. Various physical and geometrical features of the models are also discussed.

Cosmological models in alternative theory of gravity with bilinear deceleration parameter

Abstract: In this paper we have studied the exact solution of modified EFE (Einstein’s field equations) within the scope of spatially homogeneous and isotropic FLRW (Friedmann-Lemaitre-Robertson-Walker) space-time in scalar-tensor BD (Brans-Dicke) theory of gravity. For the purpose we have proposed DP (Deceleration Parameter) $q$ as a bilinear function of proper cosmic time $t$ as $q = \frac{\alpha (1-t)}{1+t}$ and $q = -\frac{\alpha t}{1+t}$ , here $\alpha $ is a non-negative constant. As per requirement we have already addressed the various aspects of cosmological models. Physical and geometric properties of the models have been also presented.

On Friedmann-Robertson-Walker model in conformal teleparallel gravity

Abstract: In this paper we use the conformal teleparallel gravity to study an isotropic and homogeneous Universe which is settled by the Friedmann–Robertson–Walker metric. The conformal symmetry demands the existence of a scalar field which works as a dark field for this model. We solve numerically the field equations then we obtain the behavior of some cosmological parameters such as the scale factor, the deceleration parameter and the energy density of the perfect fluid which is the matter field of our model. The field equations, which we called modified Friedmann equations, allow us to define a dark fluid, with dark energy density and pressure, responsible for the acceleration in the Universe, once we defined an equation of state for the dark fluid.

Reconstruction of interaction rate in holographic dark energy

Abstract: The present work is based on the holographic dark energy model with Hubble horizon as the infrared cut-off. The interaction rate between dark energy and dark matter has been reconstructed for three different parameterizations of the deceleration parameter. Observational constraints on the model parameters have been obtained by maximum likelihood analysis using the observational Hubble parameter data (OHD), type Ia supernovab data (SNe), baryon acoustic oscillation data (BAO) and the distance prior of cosmic microwave background (CMB) namely the CMB shift parameter data (CMBShift). The interaction rate obtained in the present work remains always positive and increases with expansion. It is very similar to the result obtained by Sen and Pavon [1] where the interaction rate has been reconstructed for a parametrization of the dark energy equation of state. Tighter constraints on the interaction rate have been obtained in the present work as it is based on larger data sets. The nature of the dark energy equation of state parameter has also been studied for the present models. Though the reconstruction is done from different parametrizations, the overall nature of the interaction rate is very similar in all the cases. Different information criteria and the Bayesian evidence, which have been invoked in the context of model selection, show that the these models are at close proximity of each other.

Statefinder diagnosis for holographic dark energy models in modified \(f(R,T)\) gravity

Abstract: In this paper we consider the non-viscous and viscous holographic dark energy models in modified $f(R,T)$ gravity in which the infra-red cutoff is set by the Hubble horizon. We find power-law and exponential form of scale factor for non-viscous and viscous models, respectively. It is shown that the Hubble horizon as an infra-red cut-off is suitable for both the models to explain the recent accelerated expansion. In non-viscous model, we find that there is no phase transition. However, viscous model explains the phase transition from decelerated phase to accelerated phase. The cosmological parameters like deceleration parameter and statefinder parameters are discussed to analyze the dynamics of evolution of the Universe for both the models. The trajectories for viscous model are plotted in $r$ - $s$ and $r$ - $q$ planes to discriminate our model with the existing dark energy models which show the quintessence like behavior.

LRS Bianchi type-II minimally interacting holographic dark energy model in Saez-Ballester theory of gravitation

Abstract: Field equations of Saez and Ballester (Phys. Lett. A 113:467, 1986) scalar-tensor theory are obtained in the presence of two minimally interacting fields; matter and holographic dark energy components in spatially homogeneous and anisotropic LRS Bianchi type-II space-time. An exact solution of the field equations is presented using linearly varying deceleration parameter proposed by Akarsu and Dereli (Int. J. Theor. Phys. 51:612, 2012) which represents a minimally interacting Bianchi type-II universe in Saez-Ballester theory of gravitation. Some physical and kinematical properties of the model are also studied.

Magnetised Strings in Λ-Dominated Anisotropic Universe

Abstract: In this paper, we have searched the existence of Λ-dominated anisotropic universe filled with magnetized strings. The observed acceleration of universe has been explained by introducing a positive cosmological constant Λ in the Einstein’s field equation which is mathematically equivalent to dark energy with equation of state (EOS) parameter set equal to −1. The present values of the matter and the dark energy parameters (Ω m )0 & (ΩΛ)0 are estimated for high red shift (.3 ≤ z ≤ 1.4) SN Ia supernova data’s of observed apparent magnitude along with their possible error taken from Union 2.1 compilation. It is found that the best fit value for (Ω m )0 & (ΩΛ)0 are 0.2920 & 0.7076 respectively which are in good agreement with recent astrophysical observations in the latest surveys like WMAP and Plank. Various physical parameters such as the matter and dark energy densities, the present age of the universe and the present value of deceleration parameter have been obtained on the basis of the values of (Ω m )0 & (ΩΛ)0.Also, we have estimated that the acceleration would have begun in the past at z = 0.6845 i. e. 6.2341 Gyrs before from now.

Power-law entropy-corrected holographic dark energy in Hořava-Lifshitz cosmology with Granda-Oliveros cut-off

Abstract: In this paper, we study the Power-Law Entropy-Corrected Holographic Dark Energy (PLECHDE) model in the framework of Hořava-Lifshitz cosmology considering a non-flat Universe. As infrared cut-off of the system, we choose the recently proposed Granda-Oliveros (GO) cut-off, which is a function of the Hubble parameter squared H2 and of the first time derivative of the Hubble parameter $\dot{H}$ . Moreover, the GO cut-off is characterized by two constant parameters, $\alpha$ and $\beta$ , representing the multiplying factors of the two terms forming the cut-off itself. We derive the evolutionary form of the fractional energy densities of DE, DM and curvature $\Omega_{D}'$ , $\Omega_{m}'$ and $\Omega_{k}'$ , the pressure of DE pD, the Equation-of-State (EoS) parameter of DE $\omega_{D}$ and the deceleration parameter q . Using the parametrization of the EoS parameter $\omega_{D}(z) = \omega_{0}+\omega_{1} z$ , we obtain the expressions of $\omega_{0}$ and $\omega_{1}$ . We also study the behavior of the statefinder parameters {r,s}, the snap and lerk cosmographic parameters $s_{cosmo}$ and l and the squared speed of the sound v s 2 in order to have a better comprehension of the properties of the model considered. We also calculate the present day values of the quantities we study for different values of the running parameter $\lambda$ (which is a characteristic parameter of Hořava-Lifshitz cosmology) and for different sets of values of $\alpha$ and $\beta$ . All the quantities are derived for both non-interacting and interacting DE and Dark Matter (DM).

Behaviour of the cosmological model with variable deceleration parameter

Abstract: We consider the Bianchi type-VI0 massive string universe with decaying cosmological constant $\Lambda$ . To solve Einstein's field equations, we assume that the shear scalar is proportional to the expansion scalar and that the deceleration parameter q is a linear function of the Hubble parameter H, i.e., $q=\alpha +\beta H$ , which yields the scale factor $a = e^{\frac{1}{\beta}\sqrt{2\beta t+k_{1}}}$ . The model expands exponentially with cosmic time t. The value of the cosmological constant $\Lambda$ is small and positive. Also, we discuss physical parameters as well as the jerk parameter j, which predict that the universe in this model originates as in the $\Lambda$ CDM model.

Constraints on modified Chaplygin gas from large scale structure

Abstract: We study cosmological models with modified Chaplygin gas (MCG) to determine observational constraints on its EoS parameters using the background and the growth tests data. The background test data consists of $H(z)-z$ data, Baryonic Acoustic Oscillations peak parameter, CMB shift parameter, SN Ia data and the growth test data consists of the linear growth function for the large scale structures of the universe are considered to study MCG in favor of dark energy. For a given range of redshift, the Wiggle-Z measurements and rms mass fluctuations from Ly- $\alpha $ data, employed for analyzing cosmological models numerically to constrain the MCG parameters. The Wang-Steinhardt ansatz for the growth index ( $\gamma $ ) and growth function ( $f$ ) are also considered for numerical analysis. The best-fit values of EoS parameters determined here are used to study the variation of $f$ , growth index ( $\gamma $ ), EoS parameter, squared sound speed and deceleration parameter with redshift. The constraints on the MCG parameters found here are compared with that of GCG (generalized Chaplygin gas) model for viable cosmology. Cosmologies with MCG satisfactorily describe late acceleration followed by a matter dominated phase. The range of values of EoS parameters, the associated parameters ( $f$ , $\gamma $ , $\omega $ , $\varOmega $ , $c^{2}_{s}$ , $q$ ) are also determined from observational data in order to understand the suitability of the MCG model.