Homogeneous Universe Model Research Articles

Investigation of dark energy scenarios in f(Q) gravitation theory

In order to solve the mystery of the accelerating and expanding universe model first, various dark energy candidates, such as Quintessence, Tachyon, k-essence, Phantom and DBI-essence, were investigated in detail in the [Formula: see text] modified symmetric teleparallel gravitation theory for homogeneous and isotropic FRLW universe model. The [Formula: see text] model is used to obtain solutions in [Formula: see text] theory. Also, the physical behaviors of some cosmological parameters such as pressure and density were studied. Dark energy candidates were analyzed for different values of n with various graphs.

Cosmic Evolution of Five‐dimensional Einstein Chern‐Simons Gravity Through Dark Energy Model

AbstractIn this paper, the cosmic evolution in the context of five‐dimensional Einstein Chern‐Simons gravity theory by using flat homogeneous and isotropic universe model is studied. The interaction is taken into account between dark sector of the evolving universe along with holographic dark energy model with Hubble horizon. Our study with well‐known models EChS ‐β5 and EChS ‐ for Einstein Chern‐Simons gravity theory in five dimensions are carried. Some cosmological parameters through graphical representations such as coincidence parameter u, equation of state parameter , deceleration parameter q and squared speed of sound parameter is analyzed. It is found that these cosmological parameters show consistent behavior with current cosmic scenario. Also, the behavior of generalized second law of thermodynamics in the underlying gravity theory with Bekenstein‐Hawking entropy and its validity for some fixed values of constants appearing in each model are explored.

Renyi Holographic Dark Energy Model in f(R) Gravity with Hubble's IR Cut-Off

In the present study, a homogeneous and anisotropic LRS Bianchi type-I universe model is considered with an interacting dark matter and Renyi holographic dark energy model (RHDE) in f(R) gravity. The deceleration parameter (DP) shows a signature flipping for a universe which was decelerating in past and accelerating at present epoch. Therefore, the DP is a most physically justified parameter to analyze the solution of cosmological model. In order to find an exact solution of the field equations of the model, the shear scalar is considered to be proportional to the expansion scalar. We have considered f(R) = b Rn, the depiction model of f(R) which is the function of Ricci scalar R. The physical and geometrical characteristics of the universe model have been studied.

Homogeneous and anisotropic universe models with bouncing deceleration parameter in $f(R,T)$ theory

In this study, we have investigated the cloud of string with perfect fluid (CSPF) matter distribution for the homogeneous and anisotropic (Bianchi I, III, and Kantowski-Sachs) universe models in the $f(R,T)$ theory. We have used the\, bouncing\, deceleration parameter, anisotropy parameter, and equation of state to obtain the exact solutions of field equations. The obtained physical and kinematic quantities were analyzed with the help of graphics. If the anisotropy parameter is zero, then our model becomes an isotropic model of the universe and the string tension vanishes in LRS Bianchi I metric. Finally, we discuss the need for further research.

Role of constant jerk parameter in f(R,T) gravity

In this study, a homogeneous and anisotropic Bianchi type-I universe model is considered taking the cosmological constant as a variable in the context of f (R, T) gravity. The presented model relies on a unique condition of constant jerk parameter as j = 1, which corresponds to a flat [Formula: see text]CDM model that leads to a variable deceleration parameter. The exact solution of the field equations is obtained under that condition, and the physical and geometrical features of the model are discussed through the paper. The model has been shown to be successful in explaining recent cosmological observations such as the universe’s expansion decelerates in the early universe and accelerates in the late universe, in agreement with their current data.

Redshift and redshift drift in Λ=0 quasispherical Szekeres cosmological models and the effect of averaging

Since the advent of the accelerated expanding homogeneous universe model, some other explanations for the type Ia supernova dimming have been explored, among which there are inhomogeneous models constructed with exact $\mathrm{\ensuremath{\Lambda}}=0$ solutions of Einstein's equations. They have been used either to be a one patch or to build Swiss-cheese models. The most studied ones have been the Lema\^{\i}tre-Tolman-Bondi (LTB) models. However, these models being spatially spherical, they are not well designed to reproduce the large scale structures which exhibit clusters, filaments, and nonspherical voids. This is the reason why Szekeres models, which are devoid of any symmetry, have recently come into play. In this paper, we give the equations and an algorithm to compute the redshift drift for the most general quasispherical Szekeres (QSS) models with no dark energy. We apply it to a QSS model recently proposed by Bolejko and Sussman (BSQSS model) who averaged their model to reproduce the density distribution of the Alexander and collaborators' LTB model which is able to fit a large set of cosmological data without dark energy. They concluded that their model represents a significant improvement over the observed cosmic structure description by spherical LTB models. We show here that this QSS model is ruled out by a negative cosmological redshift, i.e., a blueshift, which is not observed in the universe. We also compute a positive redshift and the redshift drift for the model of Alexander et al. and compare this redshift drift to that of the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. We conclude that the process of averaging an unphysical QSS model can lead to obtain a physical model able to reproduce our observed local universe with no dark energy need and that the redshift drift can discriminate between this model and the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. For completeness, we also compute the blueshift drift of the BSQSS model.

Consistency Conditions of f(R,G)-Gravity Field Equations for Bianchi-Type III Metric

In this paper, we study the -gravitation theory under the assumption that the standard matter-energy content of the universe is a perfect fluid with linear barotropic equation of state within the framework of Bianchi-Type III model from the class of homogeneous and anisotropic universe models. However, whether such a restriction lead to any contradictions or inconsistencies in the field equations will create an issue that needs to be examined. Under the effective fluid approach, we will be concerned mainly the field equations in an orthonormal tetrad framework with an equimolar and examined the situation of establishing the functional form of together with the scale factors, which are their solutions. Unlike similar studies, which are very few in the literature, instead of assuming preliminary solutions, we determined the consistency conditions of the field equations by assuming the matter energy content of the universe as an isotropic perfect fluid for Bianchi-Type III.

A Summary of the Homogeneous 5D Universe Creation Model: Expressed in the Dirac Second-Order Quantization Representation

A summary of the homogeneous 5D universe model is expressed in the Dirac second-order quantized representation for the magnetic monopoles, identified in terms of the Higgs Bosons, and through systematic ordered excitations of the Higgs vacuum obtained the non-homogeneous 4D Lorentz manifolds filled with masses, corresponding to making space dimension reduction projections, and thus realization of Newtonian gravity, followed by the 3D space symmetry breaking into 2D × 1D that produces the Perelmann-entropy and Ricci-Flow mappings, resulting in the realization of Poincare spheres, represented by nucleus such as Carbon 12, all the way to stars, and matter filled discs, such as stars in galaxies and 2D carbon-based molecular structures like nitrogenous bases. Finally, the forming of RNAs and DNAs, then life forms.

Collins in Wonderland

What is the asymptotic future of a scalar-field model if the assumption of isotropy is relaxed in generic, homogeneous Universe models? This paper is a continuation of our previous work on Bianchi cosmologies with a p-form field (where p ∈ {1, 3})—or equivalently: an inhomogeneous, mass-less scalar gauge field with a homogeneous gradient. In this work we investigate such matter sector in general relativity, and restrict to space-times of the particular Bianchi types VI0 and , where = {h < 0⎸h ≠ −1/9 ∪ −1}. We show that the previously found fabric of exact solutions named Wonderland are future attractors in (VI0) and (), extending the Collins perfect-fluid equilibrium set to include a p-form (with p ∈ {1, 3}). We also write down the line-element corresponding to Wonderland in and give explicit expressions for the underlying gauge-potential ϕ(t, x) corresponding to this solution. Simulation of a path approaching Wonderland in Bianchi type I is also given.

Stability analysis of coupled phantom and tachyon field models in nonlinear electrodynamics

This paper is devoted to studying the phase space portrait of FRW universe by taking different linear forms of coupling between scalar field models and dark matter with nonlinear electromagnetic effects. We introduce normalized dimensionless quantities to construct an autonomous system of equations. We evaluate critical points and respective eigenvalues for different parameters to analyze the stability of the cosmos. These points show saddle/unstable behavior for tachyon coupled field with the nonaccelerating universe. In the case of phantom energy, the stability decreases for some critical points which also represent the nonaccelerating universe. We conclude that the dynamical stability of the isotropic and homogeneous universe model reduces in the presence of nonlinear electrodynamics for tachyon as well as the phantom field.

Thermodynamics of Modified Cosmic Chaplygin Gas

We examine the thermodynamic features of an exotic fluid known as modified cosmic Chaplygin gas in the context of homogeneous isotropic universe model. For this purpose, the behavior of physical parameters is discussed that help to analyze nature of the universe. Using specific heat formalism, the validity of third law of thermodynamics is checked. Furthermore, with the help of thermodynamic entities, the thermal equation of state is also discussed. The thermodynamic stability is explored by means of adiabatic, specific heat and isothermal conditions from classical thermodynamics. It is concluded that the considered fluid configuration is thermodynamically stable and expands adiabatically for an appropriate choice of parameters.

Study of Homogeneous and Isotropic Universe in f(R,Tφ) Gravity

This paper is devoted to study the cosmological behavior of homogeneous and isotropic universe model in the context of f(R,Tφ) gravity, where φ is the scalar field. For this purpose, we follow the first-order formalism defined by H=W(φ). We evaluate Hubble parameter, effective equation of state parameter (ωeff), deceleration parameter, and potential of scalar field for three different values of W(φ). We obtain phantom era in some cases for the early times. It is found that exponential expression of W(φ) yields ωeff independent of time for flat universe and independent of model parameter otherwise. It is concluded that our model corresponds to ΛCDM for both initial and late times.

Thermodynamical stability of FRW models with quintessence

In this paper, we study the thermodynamic stability of quintessence in the background of homogeneous and isotropic universe model. For the evolutionary picture, we consider two different forms of potentials and investigate the behavior of different physical parameters. We conclude that the quintessence model expands adiabatically and this expansion is thermodynamically stable for both potentials with suitable model parameters.

Study of some chaotic inflationary models in f ( R ) $f(R)$ gravity

In this paper, we discuss inflationary scenario via scalar field and fluid cosmology for anisotropic homogeneous universe model in $f(R)$ gravity. We consider an equation of state which corresponds to quasi-de Sitter expansion and investigate the effect of anisotropy parameter for different values of deviation parameter. We evaluate potential models like linear, quadratic and quartic which correspond to chaotic inflation. We construct the observational parameters for power-law model of $f(R)$ gravity and construct the graphical analysis of tensor-scalar ratio and spectral index which indicates consistency of these parameters with Planck 2015 data.

Thermodynamics in f(G,T) Gravity

This paper explores the nonequilibrium behavior of thermodynamics at the apparent horizon of isotropic and homogeneous universe model in f(G,T) gravity (G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, resp.). We construct the corresponding field equations and analyze the first as well as generalized second law of thermodynamics in this scenario. It is found that an auxiliary term corresponding to entropy production appears due to the nonequilibrium picture of thermodynamics in first law. The universal condition for the validity of generalized second law of thermodynamics is also obtained. Finally, we check the validity of generalized second law of thermodynamics for the reconstructed f(G,T) models (de Sitter and power-law solutions). We conclude that this law holds for suitable choices of free parameters.

Study of GSLT in Curvature-Matter Coupling Gravity

In this work, we study the first and generalized second laws of thermodynamics at the apparent horizon of homogeneous and isotropic universe model in the context of f (G, T) gravity (G and T represent the Gauss-Bonnet invariant and trace of the energymomentum tensor, respectively). We formulate the corresponding field equations as well as determine the radius, temperature and entropy to analyze these laws. An extra term associated with entropy production is appeared in the first law due to the non-equilibrium treatment of thermodynamics. It is found that the universal condition is obtained to preserve the generalized second law of thermodynamics.

Cosmological reconstruction and stability in F(T,TG) gravity

This study investigates the reconstruction scheme and stability of some well-known cosmological models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] represent the torsion scalar and Gauss–Bonnet invariant torsion term, respectively. For this purpose, we consider isotropic homogeneous universe model and develop the corresponding field equations. It is found that we can reproduce cosmological evolution for power-law, de Sitter solutions, phantom/nonphantom era and [Formula: see text] cold dark matter by applying reconstruction scheme in this gravity. Finally, we discuss stability of the reconstructed power-law and de Sitter solutions as well as two well-known [Formula: see text] models. It is concluded that all these models provide stable solutions for suitable choices of the constants except power-law solutions.

Noether symmetries and anisotropic universe models in f(R, T) gravity

This paper investigates the existence of Noether symmetries of some anisotropic homogeneous universe models in non-minimally coupled f(R, T) gravity (R and T represent Ricci scalar and trace of the energy–momentum tensor). We evaluate symmetry generators and the corresponding conserved quantities for two models of this theory admitting direct and indirect non-minimal curvature–matter coupling. We also discuss exact solutions for dust as well as non-dust matter distribution and study the physical behavior of some cosmological parameters through these solutions. For dust distribution, the exact solution corresponds to power-law expansion and Einstein universe while exponential expansion appears for non-dust matter. The graphical analysis of these solutions and cosmological parameters provide consistent results with recent observations about accelerated cosmic expansion. We conclude that Noether symmetry generators and conserved quantities exist for both models.

Stability analysis of some reconstructed cosmological models inf(G,T)gravity

Abstract The aim of this paper is to reconstruct and analyze the stability of some cosmological models against linear perturbations in f ( G , T ) gravity ( G and T represent the Gauss–Bonnet invariant and trace of the energy–momentum tensor, respectively). We formulate the field equations for both general as well as particular cases in the context of isotropic and homogeneous universe model. We reproduce the cosmic evolution corresponding to de Sitter universe, power-law solutions and phantom/non-phantom eras in this theory using reconstruction technique. Finally, we study stability analysis of de Sitter as well as power-law solutions through linear perturbations.

Cosmological analysis of scalar field models in f(R,\xa0T) gravity

This paper determines the existence of Noether symmetry in non-minimally coupled f(R, T) gravity admitting minimal coupling with scalar field models. We consider a generalized spacetime which corresponds to different anisotropic and homogeneous universe models. We formulate symmetry generators along with conserved quantities through Noether symmetry technique for direct and indirect curvature–matter coupling. For dust and perfect fluids, we evaluate exact solutions and construct their cosmological analysis through some cosmological parameters. We conclude that decelerated expansion is obtained for the quintessence model with a dust distribution, while a perfect fluid with dominating potential energy over kinetic energy leads to the current cosmic expansion for both phantom as well as quintessence models.