arXiv subjects

M. Malekjani

Publications and source records attributed to M. Malekjani.

30 records · Page 2Linked to original sources

arXiv2011

The Effect of Cosmological Background Dynamics on the Spherical Collapse in MOND

The effect of background dynamics of the universe on formation of large scale structures in the framework of Modified Newtonian Dynamics (MOND) is investigated. A spherical collapse model is used for modeling the formation of the structures. This study is done in two extreme cases: ({\it i}) assuming a universe with a low-density baryonic matter without any cold dark matter and dark energy; ({\it ii}) a dark energy dominated universe with baryonic matter, without cold dark matter. We show that for the case ({\it ii}) the structures virialize at lower redshifts with larger radii compared to the low-density background universe. The dark energy slow downs the collapse of the structures. We show that our results are compatible with recent simulations of the structure formation in MOND.

gr-qc↗

arXiv2011

Cosmological implications of interacting polytropic gas dark energy model in non-flat universe

The polytropic gas model is investigated as an interacting dark energy scenario. The cosmological implications of the model including the evolution of EoS parameter $w_Λ$, energy density $Ω_Λ$ and deceleration parameter $q$ are investigated. We show that, depending on the parameter of model, the interacting polytropic gas can behave as a quintessence or phantom dark energy. In this model, the phantom divide is crossed from below to up. The evolution of $q$ in the context of polytropic gas dark energy model represents the decelerated phase at the early time and accelerated phase later. The singularity of this model is also discussed. Eventually, we establish the correspondence between interacting polytropic gas model with tachyon, K-essence and dilaton scalar fields. The potential and the dynamics of these scalar field models are reconstructed according to the evolution of interacting polytropic gas.

gr-qc↗

arXiv2011

Interacting entropy-corrected holographic scalar field models in non-flat universe

In this work we establish a correspondence between the tachyon, K-essence and dilaton scalar field models with the interacting entropy-corrected holographic dark (ECHD) model in non-flat FRW universe. The reconstruction of potentials and dynamics of these scalar fields according to the evolutionary behavior of the interacting ECHDE model are be done. It has been shown that the phantom divide can not be crossed in ECHDE tachyon model while it is achieved for ECHDE K-essence and ECHDE dilaton scenarios. At last we calculate the limiting case of interacting ECHDE model, without entropy-correction.

gr-qc↗

arXiv2011

Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis

The generalized Chaplygin gas (GCG) model in spatially flat universe is investigated. The cosmological consequences led by GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated. We show that the GCG model behaves as a general quintessence model. The GCG model can also represent the pressureless CDM model at the early time and cosmological constant model at the late time. The dependency of transition from decelerated expansion to accelerated expansion on the parameters of model is investigated. The statefinder parameters $r$ and $s$ in this model are derived and the evolutionary trajectories in $s-r$ plane are plotted. Finally, based on current observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for best fit values of the parameters of GCG model. It has been shown that although, there are similarities between GCG model and other forms of chaplygin gas in statefinder plane, but the distance of this model from the $Λ$CDM fixed point in $s-r$ diagram is shorter compare with standard chaplygin gas model.

gr-qc↗

arXiv2010

Cosmological evolution and statefinder diagnostic for new holographic dark energy model in non flat universe

In this paper, the holographic dark energy model with new infrared cut-off proposed by Granda and Oliveros has been investigated in spatially non flat universe. The dependency of the evolution of equation of state, deceleration parameter and cosmological evolution of Hubble parameter on the parameters of new HDE model are calculated. Also, the statefinder parameters $r$ and $s$ in this model are derived and the evolutionary trajectories in $s-r$ plane are plotted. We show that the evolutionary trajectories are dependent on the model parameters of new HDE model. Eventually, in the light of SNe+BAO+OHD+CMB observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for best fit values of the parameters of new HDE model.

gr-qc↗

arXiv2010

New holographic Chaplygin gas model of dark energy

In this work, we investigate the holographic dark energy model with new infrared cut-off (new HDE model) proposed by Granda and Oliveros. Using this new definition for infrared cut-off, we establish the correspondence between new HDE model and standard Chaplygin gas (SCG), generalized Chaplygin gas (GCG) and modified Chaplygin gas (MCG) scalar field models in non-flat universe. The potential and dynamics for these scalar field models, which describe the accelerated expansion of the universe are reconstructed. According to the evolutionary behavior of new HDE model, we derive the same form of dynamics and potential for different SCG, GCG and MCG models. We also calculate the squared sound speed of new HDE model as well as for SCG, GCG and MCG models and investigate the new HDE Chaplygin gas models from the viewpoint of linear perturbation theory. All results in non-flat universe are also discussed in the limiting case of flat universe, i.e. $k=0$.

gr-qc↗

arXiv2010

Agegraphic reconstruction of modified $F(R)$ and $F(\mathcal{G})$ gravities

The cosmological reconstruction of modified $F(R)$ and $F(\mathcal{G})$ gravities with agegraphic dark energy (ADE) model in a spatially flat universe without matter field is investigated by using e-folding "$N$" as a forward way. After calculating a consistent $F(R)$ in ADE's framework, we obtain conditions for effective equation of state parameter $w_{\mathrm{eff}}$, and see that reconstruction is possible for both phantom and non-phantom era. These calculations also are done for $F(\mathcal{G})$ gravity and the condition for a consistent reconstruction is obtained.

hep-th↗

arXiv2010

Cosmic Behavior, Statefinder Diagnostic and $w-w^{\prime}$ Analysis for Interacting NADE model in Non-flat Universe

We give a brief review of interacting NADE model in non-flat universe. we study the effect of spatial curvature $Ω_{k}$, interaction coefficient $α$ and the main parameter of NADE, $n$, On EoS parameter $w_{d}$ and deceleration parameter $q$. We obtain a minimum value for $n$ in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing the sign of $q$ is strongly dependent on $α$. It has been shown that the quantities $w_{d}$ and $q$ have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and $ w-w^{\prime}$ analysis in non flat universe. In non flat universe, the statefinder trajectory is discriminated by both $n$ and $α$.

gr-qc↗

arXiv2010

Agegraphic Dark Energy Model in Non-Flat Universe: Statefinder Diagnostic and $w-w^{\prime}$ Analysis

We study the interacting agegraphic dark energy (ADE) model in non-flat universe by means of statefinder diagnostic and $w-w^{\prime}$ analysis. First, the evolution of EoS parameter ($w_d$) and deceleration parameter ($q$) in terms of scale factor for interacting ADE model in non-flat universe are calculated. Dependence of $w_d$ on the ADE model parameters $n$ and $α$ in different spatial curvatures is investigated. We show that the evolution of $q$ is dependent on the type of spatial curvature, beside of dependence on parameters $n$ and $α$. The accelerated expansion takes place sooner in open universe and later in closed universe compare with flat universe. Then, we plot the evolutionary trajectories of the interacting ADE model for different values of the parameters $n$ and $α$ as well as for different contributions of spatial curvature, in the statefinder parameters plane. In addition to statefinder, we also investigate the ADE model in non-flat universe with $w-w^{\prime}$ analysis.

gr-qc↗

arXiv2010

Interacting entropy-corrected agegraphic Chaplygin gas model of dark energy

In this work, we consider the interacting agegraphic dark energy models with entropy correction terms due to loop quantum gravity. We study the correspondence between the Chaplygin gas energy density with the interacting entropy-corrected agegraphic dark energy models in non-flat FRW universe. We reconstruct the potentials and the dynamics of the interacting entropy-corrected agegraphic scalar field models. This model is also extended to the interacting entropy-corrected agegraphic generalized Chaplygin gas dark energy.

gr-qc↗

arXiv2008

Two Component Baryonic-Dark Matter Structure Formation in Top-Hat Model

In this work we extend simple top-hat model of structure formation to the two-component system made of baryonic and dark matter. We use Harrison-Zeldovich spectrum as the initial condition for the structures and calculate their evolution up to the present time. While we do not take into account some complications during the structure formation, such as the merging of galaxies, however this formalism can give us a qualitative picture from the formation of structures. We show that in this model small scale structures evolve faster than the larger ones and it predicts a down-top scenario for the structure formation. The trend of power spectrum in this model is compatible with the observations and results in $σ_8 \sim 0.8$. This formalism provides an analytic treatment of structure growth and can easily show the effect of the cosmological parameters on the formation of the structures. As an example, the effect of a parameterized dark energy model on the growth of the structures is investigated.

astro-ph↗

arXiv2008

Spherical Collapse in Modified Newtonian Dynamics (MOND)

Modeling the structure formation in the universe, we extend the spherical collapse model in the context of MOND starting with the linear Newtonian structure formation followed by the MONDian evolution. In MOND the formation of structures speed up without a need for dark matter. Starting with the top-hat over-dense distribution of the matter, the structures virialize with a power--law profile of the distribution of matter. We show that the virialization process takes place gradually from the center of the structure to the outer layers. In this scenario the smaller structures enter to the MONDian regime earlier and evolve faster, hence they are older than larger structures. We also show that the virialization of the structures occur in the MONDian regime, in which the smaller structures have stronger gravitational acceleration than the larger ones. This feature of the dynamical behavior of the structures is in agreement with this fact that the smaller structures as the globular clusters or galactic bulges have been formed earlier and need less dark matter in CDM scenario.

astro-ph↗