arXiv subjects

Abdulla Al Mamon

Publications and source records attributed to Abdulla Al Mamon.

30 records · Page 2Linked to original sources

arXiv2018

A new parametrization of dark energy equation of state leading to double exponential potential

We show that a canonical scalar field with a phenomenological form of energy density or equivalently an equation of state parameter can provide the required transition from decelerated ($q>0$) to accelerated expansion ($q<0$) phase of the universe. We have used the latest Type Ia Supernova (SNIa) and Hubble parameter datasets to constrain the model parameters. It has been found that for each of these dataset, the transition in deceleration parameter $q$ takes place at the recent past ($z<1$). The future evolution of $q$ is also discussed in the context of the model under consideration. Furthermore, using those datasets, we have reconstructed $ω_ϕ(z)$, the equation of state parameter for the scalar field. The results show that the reconstructed forms of $q(z)$ and $ω_ϕ(z)$ do not differ much from the standard $Λ$CDM value at the current epoch. Finally, the functional form of the relevant potential $V(ϕ)$ is derived by a parametric reconstruction from the observational dataset. The corresponding $V(ϕ)$ comes out to be a double exponential potential which has a number of cosmological implications. Additionally, we have also studied the effect of this particular scalar field dark energy sector on the evolution of matter over-densities and compared it with the $Λ$CDM model.

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arXiv2018

Constraints on a generalized deceleration parameter from cosmic chronometers

In this paper, we have proposed a generalized parametrization for the deceleration parameter $q$ in order to study the evolutionary history of the universe. We have shown that the proposed model can reproduce three well known $q$-parametrized models for some specific values of the model parameter $α$. We have used the latest compilation of the Hubble parameter measurements obtained from the cosmic chronometer (CC) method (in combination with the local value of the Hubble constant $H_{0}$) and the Type Ia supernova (SNIa) data to place constraints on the parameters of the model for different values of $α$. We have found that the resulting constraints on the deceleration parameter and the dark energy equation of state support the $Λ$CDM model within $1σ$ confidence level at the present epoch.

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arXiv2018

Study of thermal stability for different dark energy models

In the present work, we have made an attempt to investigate the dark energy possibility from the thermodynamical point of view. For this purpose, we have studied thermodynamic stability of three popular dark energy models in the framework of an expanding, homogeneous, isotropic and spatially flat FRW Universe filled with dark energy and cold dark matter. The models considered in this work are Chevallier-Polarski-Linder (CPL) model, Generalized Chaplygin Gas (GCG) model and Modified Chaplygin Gas (MCG) model. By considering the cosmic components (dark energy and cold dark matter) as perfect fluid, we have examined the constraints imposed on the total equation of state parameter ($w_{T}$) of the dark fluid by thermodynamics and found that the phantom nature ($w_{T}<-1$) is not thermodynamically stable. Our investigation indicates that the dark fluid models (CPL, GCG and MCG) are thermodynamically stable under some restrictions of the parameters of each model.

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arXiv2017

A parametric reconstruction of the deceleration parameter

The present work is based on a parametric reconstruction of the deceleration parameter $q(z)$ in a model for the spatially flat FRW universe filled with dark energy and non-relativistic matter. In cosmology, the parametric reconstruction technique deals with an attempt to build up a model by choosing some specific evolution scenario for a cosmological parameter and then estimate the values of the parameters with the help of different observational datasets. In this paper, we have proposed a logarithmic parametrization of $q(z)$ to probe the evolution history of the universe. Using the type Ia supernova (SNIa), baryon acoustic oscillation (BAO) and the cosmic microwave background (CMB) datasets, the constraints on the arbitrary model parameters $q_{0}$ and $q_{1}$ are obtained (within $1σ$ and $2σ$ confidence limits) by $χ^{2}$-minimization technique. We have then reconstructed the deceleration parameter, the total EoS parameter $ω_{tot}$, the jerk parameter and have compared the reconstructed results of $q(z)$ with other well-known parametrizations of $q(z)$. We have also shown that two model selection criteria (namely, Akaike information criterion and Bayesian Information Criterion) provide the clear indication that our reconstructed model is well consistent with other popular models.

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arXiv2017

Reconstruction of interaction rate in Holographic dark energy model with Hubble horizon as the infrared cut-off

This work is the reconstruction of the interaction rate of holographic dark energy whose infrared cut-off scale is set by the Hubble length. We have reconstructed the interaction rate between dark matter and the holographic dark energy for a specific parameterization of the effective equation of state parameter. We have obtained observational constraints on the model parameters using the latest Type Ia Supernova (SNIa), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) radiation datasets. We have found that for the present model, the interaction rate increases with expansion and remains positive throughout the evolution. For a comprehensive analysis, we have also compared the reconstructed results of the interaction rate with other well-known holographic dark energy models. The nature of the deceleration parameter, the statefinder parameters and the dark energy equation of state parameter have also been studied for the present model. It has been found that the deceleration parameter favors the past decelerated and recent accelerated expansion phase of the universe. It has also been found that the dark energy equation of state parameter shows a phantom nature at the present epoch.

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arXiv2016

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

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 $ϕ$ 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 $ϕ$. From our analysis, it has been found that the present model favors the standard $Λ$CDM model within $1σ$ confidence level.

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arXiv2016

Study of parametrized dark energy models with a general non-canonical scalar field

In this paper, we have considered various dark energy models in the framework of a non-canonical scalar field with a Lagrangian density of the form ${\cal L}(ϕ, X)=f(ϕ)X{\left(\frac{X}{M^{4}_{Pl}}\right)}^{α-1} - V(ϕ)$, which provides the standard canonical scalar field model for $α=1$ and $f(ϕ)=1$. In this particular non-canonical scalar field model, we have carried out the analysis for $α=2$. We have then obtained cosmological solutions for constant as well as variable equation of state parameter ($ω_ϕ(z)$) for dark energy. We have also performed the data analysis for three different functional forms of $ω_ϕ(z)$ by using the combination of SN Ia, BAO and CMB datasets. We have found that for all the choices of $ω_ϕ(z)$, the SN Ia $+$ CMB/BAO dataset favors the past decelerated and recent accelerated expansion phase of the universe. Furthermore, using the combined dataset, we have observed that the reconstructed results of $ω_ϕ(z)$ and $q(z)$ are almost choice independent and the resulting cosmological scenarios are in good agreement with the $Λ$CDM model (within the $1σ$ confidence contour). We have also derived the form of the potentials for each model and the resulting potentials are found to be a quartic potential for constant $ω_ϕ$ and a polynomial in $ϕ$ for variable $ω_ϕ$.

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arXiv2015

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

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 $ω_ϕ(z)$. 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 $ω_ϕ(z)$ and have found that the results are compatible with a $Λ$CDM universe if we consider SN Ia $+$ Hubble data but inclusion of BAO/CMB data makes $q(z)$ and $ω_ϕ(z)$ incompatible with $Λ$CDM model. The potential term for the present toy model is found to be functionally similar to a Higgs potential.

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arXiv2015

Generalized Second Law of Thermodynamics for Non-canonical Scalar Field Model with Corrected-Entropy

In this work, we have considered a non-canonical scalar field dark energy model in the framework of flat FRW background. It has also been assumed that the dark matter sector interacts with the non-canonical dark energy sector through some interaction term. Using the solutions for this interacting non-canonical scalar field dark energy model, we have investigated the validity of generalized second law (GSL) of thermodynamics in various scenarios using first law and area law of thermodynamics. For this purpose, we have assumed two types of horizons viz apparent horizon and event horizon for the universe and using first law of thermodynamics, we have examined the validity of GSL on both apparent and event horizons. Next, we have considered two types of entropy-corrections on apparent and event horizons. Using the modified area law, we have examined the validity of GSL of thermodynamics on apparent and event horizons under some restrictions of model parameters.

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arXiv2015

Study of non-canonical scalar field model using various parametrizations of dark energy equation of state

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 $Λ$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.

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arXiv2015

Cosmic acceleration in non-canonical scalar field model - An interacting scenario

In this paper we have studied the dynamics of accelerating scenario within the framework of scalar field models possessing a non-canonical kinetic term. In this toy model, the scalar field is allowed to interact with the dark matter component through a source term. We have assumed a specific form for the coupling term and then have studied the dynamics of the scalar field having a constant equation of state parameter. We have also carried out the dynamical system study of such interacting non-canonical scalar field models for power law potentials for some physically relevant specific values of the model parameters. It has been found that the only for two particular stable fixed points of the system, an accelerating solution is possible and the universe will settle down to a $Λ$CDM universe in future and thus there is no future singularity in this model.

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arXiv2014

An Interacting model of Dark Energy in Brans-Dicke theory

In this paper it is shown that in non-minimally coupled Brans-Dicke theory containing a self-interacting potential, a suitable conformal transformation can automatically give rise to an interaction between the normal matter and the Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as the quintessence matter, it has been shown that such a non-minimal coupling between the matter and the scalar field can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans-Dicke parameter $ω$. We have also studied the observational constraints on the model parameters considering the Hubble and Supernova data.

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