New holographic dark energy in bianchi- III universe with k-essence

This work is devoted to the investigation of new holographic dark energy (infrared cutoff is the Hubble radius) in locally rotationally symmetric Bianchi type-
 $I$
 universe within the framework of Saez–Ballester (Phys Lett A 113:467, 1986) scalar–tensor theory of gravitation We construct interacting and non-interacting dark energy models by solving the field equations using a relationship between the metric potentials This leads to a variable deceleration parameter model which exhibits a transition of the universe from deceleration to acceleration We evaluate various cosmological parameters of our models We have observed that the energy density parameters, equation of state and important cosmological planes (
 $\omega _{\mathit{de}} - \omega _{\mathit{de}}'$
 and $r - s$
 ) yield the results compatible with the modern observational data We have, also, discussed the stability analysis of our models

Anisotropic new holographic dark energy model in Saez–Ballester theory of gravitation

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 $w_{\Lambda}$ 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.

New holographic dark energy model with non-linear interaction

A plane symmetric Bianchi-I model is explored in f(R, T) gravity, where R is the Ricci scalar and T is the trace of energy–momentum tensor. The solutions are obtained with the consideration of a specific Hubble parameter which yields a constant deceleration parameter. The various evolutionary phases are identified under the constraints obtained for physically viable cosmological scenarios. Although a single (primary) matter source is taken, due to the coupling between matter and f(R, T) gravity, an additional matter source appears, which mimics a perfect fluid or exotic matter. The solutions are also extended to the case of a scalar field model. The kinematical behavior of the model remains independent of f(R, T) gravity. The physical behavior of the effective matter also remain the same as in general relativity. It is found that f(R, T) gravity can be a good alternative to the hypothetical candidates of dark energy to describe the present accelerating expansion of the universe.

Plane symmetric model in f ( R , T ) gravity

In this article, the analysis of Tsallis holographic dark energy (which turns into holographic dark energy for a particular choice of positive non-additivity parameter δ) in modified f (T, B) gravity with the validity of thermodynamics and energy conditions for a homogeneous and isotropic FLRW Universe has been studied. The enlightenment of the field equation towards , made possible by the fact that the model is purely accelerating, corresponds to q = −0.54 (Mamon and Das 2017 Eur. Phys. J. C 77 49). The generalized second law of thermodynamics is valid not only for the same temperature inside the horizon, but also for the apparent horizon for a change in temperature. The essential inspiration driving this article is to exhibit the applicability that the holographic dark energy achieved from standard Tsallis holographic dark energy and the components acquired from f(T, B) gravity are identical for the specific bounty of constants. The analysis of energy conditions confirms that the weak energy condition and the null energy condition are fulfilled throughout the expansion, while violation of the strong energy condition validates the accelerated expansion of the Universe. With the expansion, the model becomes a quintessence dominated model. The dominant energy condition is not observed initially when the model is filled with genuine baryonic matter, whereas it appears when the model is in the quintessence dominated era.

Energy conditions of the f(T, B) gravity dark energy model with the validity of thermodynamics

In this work, we study a flat Friedmann–Robertson–Walker universe filled with dark matter and viscous new holographic dark energy. We present four possible solutions of the model depending on the choice of the viscous term. We obtain the evolution of the cosmological quantities such as scale factor, deceleration parameter and transition redshift to observe the effect of viscosity in the evolution. We also emphasis upon the two independent geometrical diagnostics for our model, namely the statefinder and the Om diagnostics. In the first case we study new holographic dark energy model without viscous and obtain power-law expansion of the universe which gives constant deceleration parameter and statefinder parameters. In the limit of the parameter, the model approaches to $$\Lambda CDM$$
 model. In new holographic dark energy model with viscous, the bulk viscous coefficient is assumed as $$\zeta =\zeta _{0}+\zeta _{1}H$$
 , where $$\zeta _{0}$$
 and $$\zeta _{1}$$
 are constants, and H is the Hubble parameter. In this model, we obtain all possible solutions with viscous term and analyze the expansion history of the universe. We draw the evolution graphs of the scale factor and deceleration parameter. It is observed that the universe transits from deceleration to acceleration for small values of $$\zeta $$
 in late time. However, it accelerates very fast from the beginning for large values of $$\zeta $$
 . By illustrating the evolutionary trajectories in $$r-s$$
 and $$r-q$$
 planes, we find that our model behaves as an quintessence like for small values of viscous coefficient and a Chaplygin gas like for large values of bulk viscous coefficient at early stage. However, model has close resemblance to that of the $$\Lambda CDM$$
 cosmology in late time. The $$ Om$$
 has positive and negative curvatures for phantom and quintessence models, respectively depending on $$\zeta $$
 . Our study shows that the bulk viscosity plays very important role in the expansion history of the universe.

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Viscous cosmology in new holographic dark energy model and the cosmic acceleration

The aim of this paper is to study new holographic dark energy (HDE) model in modified $f(R,T)$
 gravity theory within the framework of a flat Friedmann-Robertson-Walker model with bulk viscous matter content. It is thought that the negative pressure caused by the bulk viscosity can play the role of dark energy component, and drive the accelerating expansion of the universe. This is the motive of this paper to observe such phenomena with bulk viscosity. In the specific model $f(R,T)=R+\lambda T$
 , where $R$
 is the Ricci scalar, $T$
 the trace of the energy-momentum tensor and $\lambda $
 is a constant, we find the solution for non-viscous and viscous new HDE models. We analyze new HDE model with constant bulk viscosity, $\zeta =\zeta _{0}= \text{const.}$
 to explain the present accelerated expansion of the universe. We classify all possible scenarios (deceleration, acceleration and their transition) with possible positive and negative ranges of $\lambda $
 over the constraint on $\zeta _{0}$
 to analyze the evolution of the universe. We obtain the solutions of scale factor and deceleration parameter, and discuss the evolution of the universe. We observe the future finite-time singularities of type I and III at a finite time under certain constraints on $\lambda $
 . We also investigate the statefinder and $\mathit{Om}$
 diagnostics of the viscous new HDE model to discriminate with other existing dark energy models. In late time the viscous new HDE model approaches to $\varLambda \mathit{CDM}$
 model. We also discuss the thermodynamics and entropy of the model and find that it satisfies the second law of thermodynamics.

New holographic dark energy model with constant bulk viscosity in modified $$ gravity theory

The purpose of this paper is to study the dynamics of non-interacting and interacting holographic dark energy (HDE) models in the framework of Brans–Dicke (BD) cosmology. As system’s infrared cutof...

Cosmological evolution of non-interacting and interacting holographic dark energy model in Brans–Dicke theory

We study a spatially homogeneous and anisotropic cosmological model in the Einstein gravitational theory with a minimally coupled scalar field. We consider a non-interacting combination of scalar field and perfect fluid as the source of matter components which are separately conserved. The dynamics of cosmic scalar fields with a zero rest mass and an exponential potential are studied, respectively. We find that both assumptions of potential along with the average scale factor as an exponential function of scalar field lead to the logarithmic form of scalar field in each case which further gives power-law form of the average scale factor. Using these forms of the average scale factor, exact solutions of the field equations are obtained to the metric functions which represent a power-law and a hybrid expansion, respectively. We find that the zero-rest-mass model expands with decelerated rate and behaves like a stiff matter. In the case of exponential potential function, the model decelerates, accelerates or shows the transition depending on the parameters. The isotropization is observed at late-time evolution of the Universe in the exponential potential model.

Minimally coupled scalar field cosmology in anisotropic cosmological model

In this paper, we present the bulk viscous phenomena to mimic new holographic dark energy behavior in modified f(R, T) gravity. We assume the bulk viscosity coefficient, $$\zeta$$
 in the form of $$\zeta = \zeta_{0} + \zeta_{1} H$$
 , where $$\zeta_{0} , \zeta_{1}$$
 are positive constants and H is the Hubble parameter. We obtain the exact solution of the scale factor and classify all the possible scenarios (deceleration, acceleration and their transition) of the evolution of the Universe. It is observed that the model transits from the decelerated phase to accelerated phase in early or late time depending on the values of viscous terms. For large values of viscous terms, the model always accelerates throughout the evolution. Furthermore, we also analyze two diagnostic parameters, statefinder $$\left\{ {r,s} \right\}$$
 and Om to discriminate our model with the other existing dark energy models. The evolutions of these diagnostics are shown in $$r - s,r - q$$
 and Om − z planes. It is found that the behavior of trajectories in different planes depends on the bulk viscous coefficients. A small combination of $$\zeta_{0}$$
 and $$\zeta_{1}$$
 gives the quintessence-like behavior, whereas a large combination gives Chaplygin gas-like model. However, the model approaches the ΛCDM model in the late time evolution of the Universe. The value of the effective equation of state parameter comes to be − 0.9745 which is very close to the observational data. The entropy and generalized second law of thermodynamics are valid under certain constraints. The analysis shows that the dark energy phenomena may be explained in the presence of bulk viscosity in the modified theory of gravity.

Milan Srivastava

Papers

Viscous cosmology in new holographic dark energy model and the cosmic acceleration

New holographic dark energy model with constant bulk viscosity in modified $$ gravity theory

Cosmological evolution of non-interacting and interacting holographic dark energy model in Brans–Dicke theory

Minimally coupled scalar field cosmology in anisotropic cosmological model

New holographic dark energy model with bulk viscosity in f(R, T) gravity