Higher Dimensional Cosmology with Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe

We have considered N-dimensional Einstein field equations in which four-dimensional space-time is described by a FRW metric and that of extra dimensions by an Euclidean metric. We have chosen the exponential forms of scale factors a and d numbers of b in such a way that there is no singularity for evolution of the higher dimensional Universe. We have supposed that the Universe is filled with K-essence, Tachyonic, Normal Scalar Field and DBI-essence. Here we have found the nature of potential of different scalar field and graphically analyzed the potentials and the fields for three scenario namely Emergent Scenario, Logamediate Scenario and Intermediate Scenario. Also graphically we have depicted the geometrical parameters named statefinder parameters and slow-roll parameters in the higher dimensional cosmology with the above mentioned scenarios.     

Fractional Action Cosmology: Emergent,Logamediate, Intermediate,Power Law Scenarios of the Universe and Generalized Second Law of Thermodynamics

In the framework of Fractional Action Cosmology (FAC), we study the generalized second law of thermodynamics for the Friedmann Universe enclosed by a boundary. We use the four well-known cosmic horizons as boundaries namely, apparent horizon, future event horizon, Hubble horizon and particle horizon. We construct the generalized second law (GSL) using and without using the first law of thermodynamics. To check the validity of GSL, we express the law in the form of four different scale factors namely emergent, logamediate, intermediate and power law. For Hubble, apparent and particle horizons, the GSL holds for emergent and logamediate expansions of the universe when we apply with and without using first law. For intermediate scenario, the GSL is valid for Hubble, apparent, particle horizons when we apply with and without first law. Also for intermediate scenario, the GSL is valid for event horizon when we apply first law but it breaks down without using first law. But for power law expansion, the GSL may be valid for some cases and breaks down otherwise.     

Validity of the Generalized Second Law of Thermodynamics in the Logamediate and Intermediate Scenarios of the Universe

In this work, we have investigated the validity of the generalized second law of thermodynamics in logamediate and intermediate scenarios of the universe bounded by the Hubble, apparent, particle and event horizons using and without using first law of thermodynamics. We have observed that the GSL is valid for Hubble, apparent, particle and event horizons of the universe in the logamediate scenario of the universe using first law and without using first law. Similarly the GSL is valid for all horizons in the intermediate scenario of the universe using first law. Also in the intermediate scenario of the universe, the GSL is valid for Hubble, apparent and particle horizons but it breaks down whenever we consider the universe enveloped by the event horizon.     

The Effects of Tachyonic and Phantom Fields in the Intermediate and Logamediate Scenarios of the Anisotropic Universe

In this work, we have analyzed two scenarios namely, “intermediate” and “logamadiate” scenarios for closed, open and flat anisotropic universe in presence of phantom field, normal tachyonic field and phantom tachyonic field. We have assumed that there is no interaction between the above mentioned dark energy and dark matter. In these two types of the scenarios of the Universe, the nature of the scalar fields and corresponding potentials have been investigated. In intermediate scenario, (i) the potential for normal tachyonic field decreases, (ii) the potentials for phantom tachyonic field and phantom field increase with the corresponding fields. Also in logamediate scenario, (i) the potential for normal tachyonic field increases, (ii) the potentials for phantom tachyonic field and phantom field decrease with the corresponding fields.     

On the Stability and Thermodynamics of the Dark Energy Based on Generalized Uncertainty Principle

The new agegraphic Dark Energy (NADE) model (based on generalized uncertainty principle) interacting with Dark Matter (DM) is considered in this study via power-law form of the scale factor a(t). The equation of state (EoS) parameter ω _G is observed to have a phantom-like behaviour. The stability of this model is investigated through the squared speed of sound $v_{s}^{2}$ . It is found that $v_{s}^{2}$ always stays at negative level. This indicates instability of the considered model. Moreover, validity of the generalized second law of thermodynamics has been investigated assuming that the apparent horizon is the enveloping horizon. It has been observed that the generalized second law is valid throughout the evolution of the universe.     

A Study on the New Agegraphic Dark Energy Model in the Framework of Generalized Uncertainty Principle for Different Scale Factors

In this paper, we consider the New Agegraphic Dark Energy (NADE) model interacting with pressureless Dark Matter (DM) in the framework of generalized uncertainty principle. We consider different expressions of the scale factor a(t) pertaining to the emergent, the intermediate and the logamediate scenarios of the universe. We have derived the expressions for various cosmological parameters in all the three cases and plotted the equation of state (EoS) parameter ω _D and squared speed of the sound $v_{s}^{2}$ to check the stability of the model in each case. We have observed that for emergent and intermediate cases, the EoS parameter has a quintom-like behavior and in the logamediate case it has quintessence-like behavior. The negative squared speed of sound in all of the three cases has indicated that the model is classically unstable for each choice of scale factor.     

Generalized Chaplygin Gas Model as a New Agegraphic Dark Energy in Non-flat Universe

In this paper we consider a correspondence between the new agegraphic dark energy density and generalized Chaplygin gas energy density in non-flat FRW universe. Then we reconstruct the potential and the dynamics of the scalar field which describe the generalized Chaplygin cosmology.     

Analysing Hessence Intermediate and Logamediate Universe in Loop Quantum Cosmological Background

We have discussed here Hessence inflation in Loop Quantum Cosmological background. In this work, we have emphasized on late times, taking into account various slow-roll conditions. This model has been constructed taking intermediate and logamediate scale factors. In both cases the forms of hessence field, potential, number of e-folds, slow-roll parameters are manipulated by taking the dissipative co-efficient Γ =Γ₀, where Γ₀ > 0 is a constant, in accordance with second law of thermodynamics.     

Letter: A Model of Dark Energy for the Accelerating Universe

Recent observations of large scale structure of the Universe, especially that of Type Ia supernovae, indicate that the Universe is flat and is accelerating, and that the dominant energy density in the Universe is the cosmic dark energy. We propose a model in which the cosmic effective Yang-Mills condensate familiar in particle physics plays the role of the dark energy that causes the acceleration of the Universe. Since the quantum effective Yang-Mills field in certain states has the equation of state p _y = – _y , when employed as the cosmic matter source, it naturally results in an accelerating expansion of the Universe. With the matter components ( _m 1/3) being added into the model, the composition of YM condensate and matter components can give rise to the desired equation of state w –2/3 for the Universe.     

Large Number, Dark Matter, Dark Energy, and Superstructures in the Universe

Since there may exist dark matter particles ν and δ with mass - 10^-1 e V in the universe, the superstructures with a scale of 10^19 solar masses （large number A - 10^19） appeared during the era near and before the hydrogen recombination. Since there are superstructures in the universe, there may be no necessity for the existence of dark energy. For checking the superstructure in the universe by CMB anisotropy, we need to measure CMB angular power spectrum especially around ten degrees across the sky- in more details, While neutrino u is related to electroweak unification, the fourth stable elementary particle 6 may be related to strong-gravity unification, which suggests p ＋ p^- → n ＋ δ^- and that some new baryons appeared in the TeV region.     

Study of Tachyon Warm Intermediate and Logamediate Inflationary Universe from Loop Quantum Cosmological Perspective

We have studied the tachyon intermediate and logamediate warm inflation in loop quantum cosmological background by taking the dissipative co-efficient Γ=Γ₀ (where Γ₀ is a constant) in “intermediate” inflation and Γ=V(φ), (where V(φ) is the potential of tachyonic field) in “logamediate” inflation. We have assumed slow-roll condition to construct scalar field φ, potential V, N-folds, etc. Various slow-roll parameters have also been obtained. We have analyzed the stability of this model through graphical representations.     

Generalized Second Law of Thermodynamics in Emergent Universe

In this letter, we have considered the FRW model of the emergent universe, which was presented in our previous work (Debnath, in Class. Quantum Gravity 25:205019, 2008). We have chosen one of the form of scale factor in such a way that the emergent scenario is possible in the universe. We have also considered the universe as a thermodynamical system with the horizon surface as a boundary of the system. The entropy and the radius of the event horizon have been calculated in the emergent scenario. When the emergent scenario occurs, we have shown that the generalized second law of thermodynamics is always satisfied for open, flat and closed models of the universe.     

A Single Model of Interacting Dark Energy: Generalized Phantom Energy or Generalized Chaplygin Gas

I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas, while phantom energy is ruled out as a dark energy candidate.     

Cosmological Model Universe Consisting of Two Forms of Dark Energy

Considering a spatially flat FRW metric we obtain a model universe consisting partly of quintessence form of dark energy and partly of cosmological constant form of dark energy; and after studying their physical,dynamical and kinematical properties it is found that our model is a new and viable form of model universe containing dark energy.     

Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe

A new dark energy model called “ghost dark energy” was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ _Λ = α H, where α is a constant of order \({\Lambda }^{3}_{QCD}\) and Λ _{Q C D} ～ 100M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed \({v_{s}^{2}}\) the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.     

Evolution of Dark Energy in the Open Universe

In this paper we discuss the evolution of the dark energy in the open universe under the framework of the χCDM model. It is showed that the dark energy in the open universe, which drives the universe accelerating, had strange evolution behaviors: it was in the state of negative energy and positive pressure at the early stage of evolution of the dark energy, then evolved into the phase of negative energy and negative pressure during the middle period, and evolved to have the typical features of dark energy (positive energy and negative pressure) only at the later stage.     

Dark Energy and Global Rotation of the Universe

We discuss the problem of universe acceleration driven by global rotation. The redshift-magnitude relation is calculated and discussed in the context of SN Ia observation data. It is shown that the dynamics of considered problem is equivalent to the Friedmann model with additional non-interacting fluid with negative pressure. We demonstrate that the universe acceleration increase is due to the presence of global rotation effects, although the cosmological constant is still required to explain the SN Ia data. We discuss some observational constraints coming from SN Ia imposed on the behaviour of the homogeneous Newtonian universe in which matter rotates relative local gyroscopes. In the Newtonian theory _r,0 can be identified with ^,0 (only dust fluid is admissible) and rotation can exist with _r,0 =^,0 0. However, the best-fit flat model is the model without rotation, i.e., ^,0 =0. In the considered case we obtain the limit for ^,0>-0.033 on the confidence level 68.3. We are also beyond the model and postulate the existence of additional matter which scales like radiation matter and then analyse how that model fits the SN Ia data. In this case the limits on rotation coming from BBN and CMB anisotropies are also obtained. If we assume that the current estimates are _m,0 ~ 0.3, _r,0 ~ 10^-4, then the SN Ia data show that ^,0 -0.01 (or ₀ > 2.6 · 10^-19 rad/s). The statistical analysis gives us that the interval for any matter scaling like radiation is _r,0 ( - 0.01, 0.04).