Interacting holographic dark energy with variable deceleration parameter and tachyon scalar field dark energy model in LRS Bianchi type-II universe

In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe.     

Stability analysis of holographic dark energy in Brans-Dicke cosmology

We study stability formulation of holographic dark energy in Brans-Dicke theory. The model is constrained with observations. The results verifies the cosmic acceleration in near past. With the stability analysis we find that the universe transits from quintessence to phantom state in near future while approaching a stable state.     

Plane-symmetric dark energy model with a massive scalar field

Investigation of dark energy models in the presence of scalar fields are attracting several kinds of research because they play a vital role in the discussion of a new scenario of accelerated expansion of the universe. In this paper, we obtain an exact plane-symmetric dark energy cosmological model in the presence of an attractive massive scalar field by solving Einstein field equations using some physically relevant conditions. We have obtained all the cosmological parameters corresponding to the model. We have also presented a physical discussion of our model using a graphical representation of these parameters. The results exhibit an expanding and accelerating dark energy model of the universe, which are consistent with modern cosmological observations.     

A dark energy model in a scalar tensor theory of gravitation

LRS Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in the scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). To get a determinate solution of the field equations we take the help of special law of variation for Hubble’s parameter presented by Bermann (Nuovo Cimento B 74:182, 1983) which yields a cosmological model with negative constant deceleration parameter. Some physical and kinematical properties of the model are also discussed.     

The entropy-corrected holographic dark energy in Brans-Dicke cosmology with varying mass fermions

We aim in this paper to study Brans-Dicke cosmology in the presence of varying mass fermions and a self-interaction potential. Furthermore, we also probe the entropy corrected holographic dark energy (ECHDE) in the model in two non-interacting and interacting scenarios. The model parameters are constrained by using the recent SNe Ia observational data and tested against observational data of Hubble parameter. For a comparison, we also constrained and tested the cosmological parameters in ΛCDM model with the same observational data. We show that in non of the scenarios the model prediction is better than ΛCDM model.     

Cosmology of some holographic dark energy models in chameleonic Brans-Dicke gravity

We study some holographic dark energy models in chameleonic Brans-Dicke field gravity by taking interaction between the dark energy components in FRW universe. Firstly, we take the holographic dark energy model with Granda-Oliveros cut-off and discuss interacting as well as non-interacting cases. Secondly, we consider the holographic dark energy with both power-law as well as logarithmic corrections using Hubble scale as infrared cut-off in interacting case only. We describe the evolution of some cosmological parameters for these holographic dark energy models. It is concluded that the phantom crossing can be achieved more easily in the presence of chameleonic Brans-Dicke field as compared to simple Brans-Dicke as well as Einstein’s gravity. Also, the deceleration parameter strongly confirms the accelerated expanding behavior of the universe.     

Two fluid scenario for dark energy model in Brans-Dicke theory of gravitation

In this paper, we study the evolution of the dark energy parameter in the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with barotropic fluid and dark energy in the scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 24:925, 1961). A determinate solution is presented using (i) the special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B 74:183, 1983) and (ii) trace free energy momentum tensor of the two fluid. Two cases of interacting and non-interacting fluid (barotropic and dark energy) scenario is considered and general results are obtained. The physical aspects of the results obtained are, also, discussed.     

G-corrected holographic dark energy model

Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant, G, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of G, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of G. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of G-corrected deceleration parameter for holographic dark energy model and show that the dependency of G on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for G-corrected holographic model and show that this model has a shorter distance from the observational point in s–r plane compare with original holographic dark energy model.     

Reconstruction of dark energy and equilibrium thermodynamics in Brans-Dicke theory

Both dark energy and the thermodynamics on apparent horizon in cosmology have been broadly investigated in recent several years. In order to maintain the continuity equation of the total matter in the universe, a new interacting dark energy in the framework of Brans-Dicke theory is proposed. Considering this new interacting dark energy, an equilibrium thermodynamics in Brans-Dicke theory is constructed successfully. Moreover, this new interacting dark energy can be regarded as arising from the “Holographic Dark Energy” models.     

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

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.     

Tsallis holographic dark energy model with observational constraints in the higher derivative theory of gravity

The present study deals with a Tsallis holographic dark energy model in a flat Friedmann-Lamatire-Rbertson-Walker space-time geometry in the context of higher derivative theory of gravity. We have solved the field equations by applying energy conservation-law in non-interacting case and have obtained such a scale factor $a\left(\tau \right)={\left[\sinh \left(\sqrt{2a_1}\tau \right)\right]}^{\frac{1}{2}}$ where $a_1$ is called as model parameter which shows transit phase evolution of the universe (decelerating to accelerating). Using this scale factor we have obtained the various cosmological parameters viz. Hubble parameter $H$, deceleration parameter (DP) $q$, jerk $j$, snap $s$, lerk $l$ and max-out $m$. Constraining on Hubble parameters $H\left(z\right)$ by the observational data of $H\left(z\right)$ we have obtained the present values of $H_0$, $a_0$ and $a_1$ and by using these constrained values, we have studied other cosmological parameters. Taking the constant equation of state (EoS) ${\omega }_m$ for ordinary matter, we have investigated the effective behaviour of various cosmological parameters and energy conditions in our model. We have observed the present values of $\{t_0,H_0,q_0,j_0,s_0,l_0,m_0,{\omega }_{d{e}_0},{\omega }_0^{\left(eff\right)}\}$ and discussed with $\Lambda$CDM model. We have found the age of the present universe $t_0=13.05$ Gyrs, present value of DP $q_0=-0.8065$ and transition point $z_t=0.748$ which are compatible with several observational results.     

A bianchi type-III cosmological model in Brans-Dicke theory for vacuum field

An exact solution of Brans-Dicke (B-D) field equations for the metric tensor of a spatially homogeneous Bianchi type-III configuration has been obtained for vacuum field. It is shown that in the limiting case the solution reduces to that of Einstein field equations in vacuum.     

Power-law and logarithmic entropy-corrected Ricci viscous dark energy and dynamics of scalar fields

In this work, I consider the logarithmic-corrected and the power-law corrected versions of the holographic dark energy (HDE) model in the non-flat FRW universe filled with a viscous Dark Energy (DE) interacting with Dark Matter (DM). I propose to replace the infra-red cut-off with the inverse of the Ricci scalar curvature R. I obtain the equation of state (EoS) parameter ω _Λ , the deceleration parameter q and the evolution of energy density parameter $\varOmega_{D}'$ in the presence of interaction between DE and DM for both corrections. I study the correspondence of the logarithmic entropy corrected Ricci Dark Dnergy (LECRDE) and power-law entropy corrected Ricci Dark Energy (PLECRDE) models with the the Modified Chaplygin Gas (MCG) and some scalar fields including tachyon, K-essence, dilaton and quintessence. I also make comparisons with previous results.     

Generalized holographic dark energy model in the Hubble length

We generalize the holographic dark energy model described in Hubble length IR cutoff by assuming a slowly time varying function for holographic parameter c ². We calculate the evolution of EoS parameter and the deceleration parameter as well as the evolution of dark energy density parameter of the model in flat FRW universe. We show that in this model the phantom line is crossed from quintessence regime to phantom regime which is in agreement with observation. The evolution of deceleration parameter of the model indicates the transition from decelerated to accelerated expansion consistently with observation. Eventually, we show that the holographic dark energy model with Hubble horizon IR cutoff can interpret the pressureless dark matter era at the early time and dark energy dominated phase later. The singularity of the model is also calculated.     

Interacting Ricci dark energy with logarithmic correction

Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area A of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter ω _Λ, the deceleration parameter q and W_D￠\Omega_{D}' in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model.