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Showing papers on "Deceleration parameter published in 2015"


Journal ArticleDOI
TL;DR: In this paper, a review of different theoretical topics associated with interaction in the dark sector is presented, including linear and nonlinear interactions which depend on the dark matter and dark energy densities.
Abstract: In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe), with interacting dark energy and dark matter, have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model.

209 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated whether or not the Big Rip can be avoided in the locally rotationally symmetric (LRS) Bianchi type-I cosmological models in f(R,T) theory of gravity.
Abstract: The locally rotationally symmetric (LRS) Bianchi type-I cosmological models have been investigated in f(R,T) theory of gravity, where R is the Ricci scalar and T is the trace of the energy momentum tensor, for some choices of the functional f(R,T)=f 1(R)+f 2(T). The exact solutions of the field equations are obtained for the linearly varying deceleration parameter q(t) proposed by Akarsu and Dereli (2012). 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. It is interesting to note that in one of the model, the universe ends with a big rip. By taking different functional forms for f 2(T) we have investigated whether or not the Big Rip can be avoided. We found that, the Big Rip situation can not be avoided and may be inherent in the linearly varying deceleration parameter. We have also applied the State-finder diagnostics to get the geometrical dynamics of the universe at different phases.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the authors revisited the kink-like parametrization of the deceleration parameter q(z), which considers a transition, at $z_t$, from cosmic decelerations to acceleration.
Abstract: We revisit the kink-like parametrization of the deceleration parameter q(z), which considers a transition, at $z_t$, from cosmic deceleration to acceleration. In this parametrization the initial, at $z \gg z_t$, value of the q-parameter is $q_i$, its final, z=-1, value is $q_f$ and the duration of the transition is parametrized by $\tau$. By assuming a flat space geometry we obtain constraints on the free parameters of the model using recent data from type Ia supernovae, BAO, 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 $H_0$, allowing us to explore the influence of different priors when marginalizing over this parameter. We also study the importance of the CMB information in the results by considering data from WMAP7, WMAP9 and Planck. We show that the contours and best fit do not depend much on the different CMB data used and that the considered new BAO data is responsible for most of the improvement in the results. Assuming a flat space geometry, $q_i=1/2$ and expressing the present value of the deceleration parameter $q_0$ as a function of the other three free parameters, we obtain $z_t=0.67^{+0.10}_{-0.08}$, $\tau=0.26^{+0.14}_{-0.10}$ and $q_0=-0.48^{+0.11}_{-0.13}$, at 68\% of confidence level, with an uniform prior over $H_0$. If in addition we fix $q_f=-1$, as in flat $\Lambda$CDM, DGP and Chaplygin quartessence that are special models described by our parametrization, we get $z_t=0.66^{+0.03}_{-0.04}$, $\tau=0.33^{+0.04}_{-0.04}$ and $q_0=-0.54^{+0.05}_{-0.07}$, in excellent agreement with flat $\Lambda$CDM for which $\tau=1/3$. We also obtain for flat wCDM, another dark energy model described by our parametrization, the constraint on the equation of state parameter -1.22 < w < -0.78 at more than 99% confidence level.

63 citations


Journal ArticleDOI
TL;DR: Anisotropic dark energy model with dynamic pressure anisotropies along different spatial directions is constructed at the backdrop of a spatially homogeneous diagonal Bianchi type V (BV) spacetime in the framework of General Relativity as discussed by the authors.
Abstract: Anisotropic dark energy model with dynamic pressure anisotropies along different spatial directions is constructed at the backdrop of a spatially homogeneous diagonal Bianchi type V (BV) spacetime in the framework of General Relativity. A time varying deceleration parameter generating a hybrid scale factor is considered to simulate a cosmic transition from early deceleration to late time acceleration. We found that the pressure anisotropies along the y- and z-axes evolve dynamically and continue along with the cosmic expansion without being subsided even at late times. The anisotropic pressure along the x-axis becomes equal to the mean fluid pressure. At a late phase of cosmic evolution, the model enters into a phantom region. From a statefinder diagnosis, it is found that the model overlaps with ΛCDM at late phase of cosmic time.

62 citations


Journal ArticleDOI
TL;DR: In this paper, the evolution of the cosmological parameters, namely, the deceleration parameter $q(z)$ and the parameter of effective equation of state in a universe containing, besides ordinary matter and dark energy, a self-interacting (collisional) matter, in the generalized $f(R,T)$ theory of gravity, where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively.
Abstract: We study the evolution of the cosmological parameters, namely, the deceleration parameter $q(z)$ and the parameter of effective equation of state in a Universe containing, besides ordinary matter and dark energy, a self-interacting (collisional) matter, in the generalized $f(R,T)$ theory of gravity, where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized Friedmann-Robertson-Walker equations and the equation of continuity and obtain a differential equation in $H(z)$, and we solve it numerically for studying the evolution of the cosmological parameters. Two $f(R,T)$ models are considered. The results with collisional matter are compared with the ones of the $\mathrm{\ensuremath{\Lambda}}$ cold dark matter model, and also with the model where only noncollisional matter exists. The curves show that the models are acceptable because the values found for ${w}_{\text{eff}}$ are consistent with observed data.

62 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined observational constraints on the power law cosmology; essentially dependent on two parameters H0 (Hubble constant) and q (deceleration parameter).
Abstract: In this paper, we examine observational constraints on the power law cosmology; essentially dependent on two parameters H0 (Hubble constant) and q (deceleration parameter). We investigate the constraints on these parameters using the latest 28 points of H(z) data and 580 points of Union2.1 compilation data and, compare the results with the results of ΛCDM . We also forecast constraints using a simulated data set for the future JDEM, supernovae survey. Our studies give better insight into power law cosmology than the earlier done analysis by Kumar [arXiv:1109.6924] indicating it tuning well with Union2.1 compilation data but not with H(z) data. However, the constraints obtained on and i.e. H0 average and q average using the simulated data set for the future JDEM, supernovae survey are found to be inconsistent with the values obtained from the H(z) and Union2.1 compilation data. We also perform the statefinder analysis and find that the power-law cosmological models approach the standard ΛCDM model as q → −1. Finally, we observe that although the power law cosmology explains several prominent features of evolution of the Universe, it fails in details.

56 citations


Journal ArticleDOI
TL;DR: In this article, three models of f(R) modified gravity including higher order terms based on different equation of state parameters were studied, and the behavior of some important cosmological parameters, such as the Hubble expansion H parameter and the deceleration parameter q, were obtained using numerical analysis.
Abstract: In this paper, we study three models of f(R) modified gravity including higher order terms based on different equation of state parameters. We also assume variable G and Λ. Using numerical analysis, we obtain the behavior of some important cosmological parameters, like the Hubble expansion H parameter and the deceleration parameter q. Statefinder diagnostics are also performed for all models.

48 citations


Journal ArticleDOI
TL;DR: In this paper, the Friedmann-Robertson-Walker universe containing viscous fluid and matter creation is considered in the modified f(R,T) theory of gravitation, which is an arbitrary function of the Ricci scalar R and the trace T of the energy-momentum tensor.
Abstract: The Friedmann–Robertson–Walker Universe containing viscous fluid and matter creation is considered in the modified f(R,T) theory of gravitation, which is an arbitrary function of the Ricci scalar R and the trace T of the energy-momentum tensor. We assume the bulk viscosity and the matter creation as two independent processes as discussed by Progogine et al. (1988, 1989). The effects of bulk viscosity and matter creation are investigated by considering the general form of bulk viscous coefficient ζ=ζ 0+ζ 1 H and particle creation rate Γ(t)=3βH. Assuming a particular class of f(R,T)=R+2f(T), where f(T)=αT, various forms of the scale factor are obtained with constant and time-dependent bulk viscous coefficient using equation of state p=(γ−1)ρ. All possible (deceleration, acceleration and their transitions) evolutions of the Universe are discussed by constraining the models on β, ζ 0 and ζ 1 in case of time-dependent deceleration parameter for positive and negative values of α. A big-rip singularity is observed for γ<0 at a finite value of cosmic time with some restrictions on parameters. It is also noted that the finite time big-rip singularity can be removed for a specific range of α in phantom region. The role of bulk viscosity and matter creation are discussed in detail through the tables and graphs of variation of deceleration parameter and the scale factor.

44 citations


Journal ArticleDOI
TL;DR: In this article, a cosmological model dominated by bulk viscous matter with a total bulk viscosity coefficient proportional to the velocity and acceleration of the expansion of the universe was considered.
Abstract: We consider a cosmological model dominated by bulk viscous matter with a total bulk viscosity coefficient proportional to the velocity and acceleration of the expansion of the universe in such a way that $$\zeta =\zeta _{0}\,+\,\zeta _{1}\frac{\dot{a}}{a}\,+\,\zeta _{2}\frac{\ddot{a}}{\dot{a}}.$$ We show that there exist two limiting conditions in the bulk viscous coefficients ( $$\zeta _{0}$$ , $$\zeta _{1}$$ , $$\zeta _{2}$$ ) which correspond to a universe having a Big Bang at the origin, followed by an early decelerated epoch and then making a smooth transition into an accelerating epoch. We have constrained the model using the type Ia Supernovae data, evaluated the best estimated values of all the bulk viscous parameters and the Hubble parameter corresponding to the two limiting conditions. We found that even though the evolution of the cosmological parameters are in general different for the two limiting cases, they show identical behavior for the best estimated values of the parameters from both limiting conditions. A recent acceleration would occur if $$\tilde{\zeta }_{0}+\tilde{\zeta }_{1}>1$$ for the first limiting conditions and if $$\tilde{\zeta }_{0}+\tilde{\zeta }_{1}<1$$ for the second limiting conditions. The age of the universe predicted by this model is found to be less than that predicted from the oldest galactic globular clusters. The total bulk viscosity seems to be negative in the past and becomes positive when $$z\le 0.8$$ . So the model violates the local second law of thermodynamics. However, the model satisfies the generalized second law of thermodynamics at the apparent horizon throughout the evolution of the universe. We also made a statefinder analysis of the model and found that it is distinguishably different from the standard $$\varLambda $$ CDM model at present, but it shows a de Sitter type behavior in the far future of the evolution.

43 citations


Journal ArticleDOI
TL;DR: In this article, anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans-Dicke theory with a self-interacting potential.
Abstract: Anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans–Dicke theory with a self-interacting potential. A unified dark fluid characterised by a linear equation of state is considered as the source of dark energy. The shear scalar is considered to be proportional to the expansion scalar simulating an anisotropic relationship among the directional expansion rates. The dynamics of the universe in the presence of a unified dark fluid in anisotropic background have been discussed. The presence of an evolving scalar field makes it possible to get an accelerating phase of expansion even for a linear relationship among the directional Hubble rates. It is found that the anisotropy in expansion rates does not affect the scalar field, the self-interacting potential, but it controls the non-evolving part of the Brans–Dicke parameter.

40 citations


Journal ArticleDOI
TL;DR: In this article, a cosmokinematics approach is used to study the accelerated expansion of the universe and the deceleration parameter, q(z), is parametrized to constrain the transition redshift (zt) at which the expansion goes from a decelerating to an accelerating phase.
Abstract: In this paper, we use the cosmokinematics approach to study the accelerated expansion of the Universe. This is a model independent approach and depends only on the assumption that the Universe is homogeneous and isotropic and is described by the FRW metric. We parametrize the deceleration parameter, q(z), to constrain the transition redshift (zt) at which the expansion of the Universe goes from a decelerating to an accelerating phase. We use three different parametrizations of q(z) namely, qI(z)=q1+q2z, qII (z) = q3 + q4 ln (1 + z) and qIII (z)=½+q5/(1+z)2. A joint analysis of the age of galaxies, strong lensing and supernovae Ia data indicates that the transition redshift is less than unity i.e. zt < 1. We also use a nonparametric approach (LOESS+SIMEX) to constrain zt. This too gives zt < 1 which is consistent with the value obtained by the parametric approach.

Journal ArticleDOI
TL;DR: In this article, a cosmological model that unifies inflation, deceleration and acceleration phases of expansion history by a BIonic system is proposed, where two coupled universes, brane and antibrane, are created interacting each other through a wormhole and inflate.

Journal ArticleDOI
TL;DR: In this paper, a nonequilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe.
Abstract: The paper deals with nonequilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe. Using Friedmann’s equations, it is shown that the deceleration parameter () can be obtained from the knowledge of the particle production rate (). Motivated by thermodynamical point of view, cosmological solutions are evaluated for the particle creation rates in three cosmic phases, namely, inflation, matter dominated era, and present late time acceleration. The deceleration parameter () is expressed as a function of the redshift parameter (), and its variation is presented graphically. Also, statefinder analysis has been presented graphically in three different phases of the universe. Finally, two noninteracting fluids with different particle creation rates are considered as cosmic substratum, and deceleration parameter () is evaluated. Whether more than one transition of is possible or not is examined by graphical representations.

Journal ArticleDOI
TL;DR: In this paper, the exact solutions of Bianchi type V spacetime in f(R, T) theory of gravity were investigated using assumptions of the variation law of Hubble parameter and constant deceleration parameter.
Abstract: The main purpose of this paper is to explore the exact solutions of Bianchi type V spacetime in f(R, T) theory of gravity (Harko et al. 2011). In this context, two exact solutions are investigated using assumptions of the variation law of Hubble parameter and constant deceleration parameter. The first solution corresponds to a singular model while the second solution gives a non-singular model of the universe. The physical quantities for these models are calculated. Moreover, the energy density and pressure of the universe is discussed in each case.

Journal ArticleDOI
TL;DR: In this paper, the existence of LRS Bianchi-I dark energy model in f(R,T) gravity with hybrid law expansion was investigated and it was shown that an extra acceleration is always present due to coupling between matter and geometry.
Abstract: In this paper, we search the existence of LRS Bianchi-I dark energy model in f(R,T) gravity with hybrid law expansion. Einstein’s field equations have been solved by taking into account the hybrid expansion law for scale factor that yields time dependent deceleration parameter (DP). We observe that in f(R,T) gravity, an extra acceleration is always present due to coupling between matter and geometry. We examine the nature of cosmological parameters and also discuss the physical properties of universe.

Journal ArticleDOI
TL;DR: In this paper, the authors considered a spatially flat FRW universe filled with pressureless matter and dark energy and derived a divergence free parametrization of the deceleration parameter.
Abstract: In this paper, we have considered a spatially flat FRW universe filled with pressureless matter and dark energy. We have considered a phenomenological parametrization of the deceleration parameter $q(z)$ and from this we have reconstructed the equation of state for dark energy $\omega_{\phi}(z)$. This divergence free parametrization of the deceleration parameter is inspired from one of the most popular parametrization of the dark energy equation of state given by Barboza and Alcaniz. Using the combination of datasets (SN Ia $+$ Hubble $+$ BAO/CMB), we have constrained the transition redshift $z_{t}$ (at which the universe switches from a decelerating to an accelerating phase) and have found the best fit value of $z_{t}$. We have also compared the reconstructed results of $q(z)$ and $\omega_{\phi}(z)$ and have found that the results are compatible with a $\Lambda$CDM universe if we consider SN Ia $+$ Hubble data but inclusion of BAO/CMB data makes $q(z)$ and $\omega_{\phi}(z)$ incompatible with $\Lambda$CDM model. The potential term for the present toy model is found to be functionally similar to a Higgs potential.

Journal ArticleDOI
TL;DR: In this article, the authors investigated spatially homogeneous and totally anisotropic Bianchi type-III cosmological models in the theory based on Lyra's geometry in Gauss normal gauge in the presence of an attractive massive scalar field.
Abstract: Spatially homogeneous and totally anisotropic Bianchi type-III cosmological models in the theory based on Lyra’s geometry in Gauss normal gauge in the presence of an attractive massive scalar field have been investigated. To get the deterministic model in terms of cosmic time, it has been assumed that the expansion scalar Θ in the models is proportional to the shear scalar σ. Two models, one with variable deceleration parameter and another with constant deceleration parameter have been discussed. To discuss the model with constant deceleration parameter, we have used the special law of variation for Hubble’s parameter proposed by (Berman Nuovo Cimento 74B, 184, 1983). The physical and geometrical properties of the models have been discussed. The energy conditions of the models are verified. It has been concluded that one of the universe models approaches to isotropy through the evolution of the universe, in some special cases.

Journal ArticleDOI
TL;DR: In this article, a tilted Friedmann model is used to examine whether the deceleration parameter measured in the rest frame of the bulk flow can differ from that of the actual universe due to relative motion effects alone.
Abstract: Large-scale peculiar motions are believed to reflect the local inhomogeneity and anisotropy of the Universe, triggered by the ongoing process of structure formation. As a result, realistic observers do not follow the smooth Hubble flow but have a peculiar ``tilt'' velocity relative to it. Our local group of galaxies, in particular, moves with respect to the universal expansion at a speed of roughly $600\text{ }\text{ }\mathrm{km}/\mathrm{sec}$. Relative motion effects are known to interfere with the observations and their interpretation. The strong dipolar anisotropy seen in the cosmic microwave background, for example, is not treated as a sign of real universal anisotropy, but as a mere artifact of our peculiar motion relative to the Hubble flow. With these in mind, we look into the implications of large-scale bulk motions for the kinematics of their associated observers, by adopting a tilted Friedmann model. Our aim is to examine whether the deceleration parameter measured in the rest frame of the bulk flow can differ from that of the actual Universe due to relative-motion effects alone. We find that there is a difference, which depends on the speed as well as the scale of the bulk motion. The faster and the smaller the drifting domain, the larger the difference. In principle, this allows relatively slow peculiar velocities to have a disproportionately strong effect on the value of the deceleration parameter measured by observers within bulk flows of, say, a few hundred megaparsecs. In fact, under certain circumstances, it is even possible to change the sign of the deceleration parameter. It goes without saying that all these effects vanish identically in the Hubble frame, which makes them an illusion and mere artifact of the observers' relative motion.

Journal ArticleDOI
TL;DR: In this paper, the exact solutions of Einstein's field equations are obtained by applying the special law of variation of Hubble parameter that yields constant values of the deceleration parameter and using a special form of decelerated parameter.
Abstract: The spatially homogeneous and anisotropic Bianchi type-V universe filled with interacting Dark matter and Holographic dark energy has been studied. The exact solutions of Einstein’s field equations are obtained by (i) applying the special law of variation of Hubble parameter that yields constant values of the deceleration parameter and (ii) using a special form of deceleration parameter. It has been observed that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike $\varLambda$ CDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The physical and geometrical aspects of the models are also discussed.

Posted Content
TL;DR: In this article, the authors propose a new model that allows to unify inflation, deceleration and acceleration phases of expansion history in the BIonic system, which is consistent with previous prediction and cosmological experiments.
Abstract: In this research, we propose a new model that allows to unify inflation, deceleration and acceleration phases of expansion history in BIonic system. In this model, in the beginning, there have been $k$ black fundamental strings that transited to the BIon configuration at a corresponding point. At this point, two universe brane and universe antibrane have been created, interacted with each other via one wormhole and inflated. With decreasing temperature, the energy of this wormhole flowed into universe branes and lead to inflation. After a short time, wormhole died, inflation ended and deceleration epoch started. With approaching two universe brane and antibrane together, tachyon was born, grew and caused creation of one new wormhole. At this time, two universe brane and antibrane connected again and late-time acceleration era of the universe began. We compare our model with previous unified phantom model and observational data and obtain some cosmological parameters like temperature in terms of time. We also find that deceleration parameter is negative during inflation and late-time acceleration epochs and positive during deceleration era. This means that our model is consistent with previous prediction and cosmological experiments.

Journal ArticleDOI
TL;DR: In this article, the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analyzed.
Abstract: In this paper the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter q and the equation state w Λ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and dark energy densities are of the same order for a long period of time, avoiding the so-called coincidence problem. We have also made the correspondence of the model with the dark energy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.

Journal ArticleDOI
TL;DR: In this paper, the authors considered f(R,T) modified theory of gravity in which the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor.
Abstract: We consider f(R,T) 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.

Journal ArticleDOI
TL;DR: In this article, the authors constructed a cosmological model to explain the cosmology constant problem and found that the survival probability of unstable states is a decreasing function of the cosomological time and has the inverse power-like form.
Abstract: We construct the cosmological model to explain the cosmological constant problem. We built the extension of the standard cosmological model $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ by consideration of decaying vacuum energy represented by the running cosmological term. From the principles of quantum mechanics one can find that in the long-term behavior survival probability of unstable states is a decreasing function of the cosmological time and has the inverse powerlike form. This implies that cosmological constant ${\ensuremath{\rho}}_{\mathrm{vac}}=\mathrm{\ensuremath{\Lambda}}(t)={\mathrm{\ensuremath{\Lambda}}}_{\text{bare}}+\frac{\ensuremath{\alpha}}{{t}^{2}}$ where ${\mathrm{\ensuremath{\Lambda}}}_{\text{bare}}$ and $\ensuremath{\alpha}$ are constants. We investigate the dynamics of this model using dynamical system methods due to a link to the $\mathrm{\ensuremath{\Lambda}}(H)$ cosmologies. We have found the exact solution for the scale factor as well as the indicators of its variability like the deceleration parameter and the jerk. From the calculation of the jerk we obtain a simple test of the decaying vacuum in the Friedman-Robertson-Walker universe. Using astronomical data [SNIa, $H(z)$, CMB, BAO] we have estimated the model parameters and compared this model with the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Our statistical results indicate that the decaying vacuum model is a little worse than the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. But the decaying vacuum cosmological model explains the small value of the cosmological constant today.

Journal ArticleDOI
TL;DR: In this paper, an effective quintessence scalar field with a power-law potential interacting with a barotropic fluid was considered, where q is a deceleration parameter.
Abstract: In this paper, we consider an effective quintessence scalar field with a power-law potential interacting with a P b =ξqρ b barotropic fluid as a first model, where q is a deceleration parameter. For the second model we assume viscous polytropic gas interacting with the scalar field. We investigate problem numerically and analyze behavior of different cosmological parameter concerning to components and behavior of Universe. We also compare our results with observational data to fix parameters of the models. We find some instabilities in the first model which may disappear in the second model for the appropriate parameters. Therefore, we can propose interacting quintessence dark energy with viscous polytropic gas as a successful model to describe Universe.

Journal ArticleDOI
TL;DR: In this paper, it was shown that holographic cosmology implies an evolving Hubble radius c 1 u RH = −1 + 3m in the presence of a dimensionless matter density m scaled to the closure density 3H 2 /8�G, where c denotes the velocity of light and H and G denote the Hubble parameter and Newton's constant.
Abstract: It is shown that holographic cosmology implies an evolving Hubble radius c 1 u RH = −1 + 3m in the presence of a dimensionless matter density m scaled to the closure density 3H 2 /8�G, where c denotes the velocity of light and H and G denote the Hubble parameter and Newton’s constant. It reveals a dynamical dark energy and a sixfold increase in gravitational attraction to matter on the scale of the Hubble acceleration. It reproduces the transition redshift zt ≃ 0.4 to the present epoch of accelerated expansion and is consistent with (q0,(dq/dz)0) of the deceleration parameter q(z) = q0 + (dq/dz)0z observed in Type Ia supernovae.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the Einstein field equations for two classes of gravity in presence of cosmological constant and quadratic equation of state (EoS) in the context of the Bianchi type-I universe.
Abstract: Bianchi type-I universe is analyzed in this article in the context of $f(R,T)$ gravity. We have solved the Einstein’s field equations for two classes of $f(R,T)$ gravity in presence of cosmological constant $\varLambda$ and quadratic equation of state (EoS) $p=\alpha\rho^{2}-\rho$ , where $\alpha eq0$ is a constant. To obtained the solutions we have used the scale factor of the form $\mathcal{R}(t)=(t^{\beta}e^{t})^{\frac {1}{n}}$ and such type of scale factor produce time dependent deceleration parameter. Also we have studied some physical and kinematical properties of the models.

Journal ArticleDOI
TL;DR: In this paper, the authors used cosmokinematics to study the accelerated expansion of the universe and showed that the transition redshift is less than unity, i.e. $z_t < 1.
Abstract: In this paper, we use the Cosmokinematics approach to study the accelerated expansion of the Universe. This is a model independent approach and depends only on the assumption that the Universe is homogeneous and isotropic and is described by the FRW metric. We parametrize the deceleration parameter, $q(z)$, to constrain the transition redshift ($z_t$) at which the expansion of the Universe goes from a decelerating to an accelerating phase. We use three different parametrizations of $q(z)$ namely, $q_\I(z)=q_{\textnormal{\tiny\textsc{1}}}+q_{\textnormal{\tiny\textsc{2}}}z$, $q_\II (z) = q_\3 + q_\4 \ln (1 + z)$ and $q_\III(z)=\frac{1}{2}+\frac{q_{\textnormal{\tiny\textsc{5}}}}{(1+z)^2}$. A joint analysis of the age of galaxies, strong lensing and supernovae Ia data indicates that the transition redshift is less than unity i.e. $z_t<1$. We also use a nonparametric approach (LOESS+SIMEX) to constrain $z_t$. This too gives $z_t<1$ which is consistent with the value obtained by the parametric approach.

Journal ArticleDOI
TL;DR: In this paper, the authors tried to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space-time.
Abstract: In this present work, we try to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space–time. In this context, we have considered four different parametrizations of the equation of state parameter of the non-canonical scalar field. Under this scenario, analytical solutions for various cosmological parameters have been found out. It has been found that the deceleration parameter shows a smooth transition from a positive value to some negative value which indicates that the universe was undergoing an early deceleration followed by late time acceleration which is essential for the structure formation of the universe. With these four parametrizations, the future evolution of the models are also discussed. It has been found that one of the models (Generalized Chaplygin gas model, GCG) mimics the concordance $$\Lambda $$ CDM in the near future, whereas two other models (CPL and JBP) diverge due to future singularity. Finally, we have studied these theoretical models with the latest datasets from SN Ia $$+$$ H(z) $$+$$ BAO/CMB.

Journal ArticleDOI
TL;DR: In this paper, the dark energy model with equation of state (EoS) parameter is derived for a non-static plane symmetric space-time filled with a perfect fluid source in the framework of f (R, T) gravity.
Abstract: The dark energy model with equation of state (EoS) parameter is derived for a non-static plane symmetric space-time filled with a perfect fluid source in the framework of f (R, T) gravity (Harko et al., arXiv: 1104.2669v2 [gr-qc], 2011). To obtain a determinate solution, a special form of deceleration parameter (DP) is used. We have assumed that the relation between metric potentials and the EoS parameter is proportional to the skewness parameter. It is observed that the EoS parameter, and the skewness parameter in the model turn out to be functions of cosmic time. Some physical and kinematical properties of the model are also discussed.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the viable exponential gravity in the metric formalism with $f(R)=-\beta R_s (1-e^{-R/R_s}), and the latest sample of the Hubble parameter measurements with 23 data points was used to place bounds on this exponential gravity model.
Abstract: We investigate the viable exponential $f(R)$ gravity in the metric formalism with $f(R)=-\beta R_s (1-e^{-R/R_s})$. The latest sample of the Hubble parameter measurements with 23 data points is used to place bounds on this $f(R)$ model. A joint analysis is also performed with the luminosity distances of Type Ia supernovae and baryon acoustic oscillations in the clustering of galaxies, and the shift parameters from the cosmic microwave background measurements, which leads to $0.240 1.47$ at 1$\sigma$ confidence level. The evolutions of the deceleration parameter $q(z)$ and the effective equations of state $\omega_{de}^{eff}(z)$ and $\omega_{tot}^{eff}(z)$ are displayed. By taking the best-fit parameters as prior values, we work out the transition redshift (deceleration/acceleration) $z_T$ to be about 0.77. It turns out that the recent observations are still unable to distinguish the background dynamics in the $\Lambda$CDM and exponential $f(R)$ models.