Investigating cosmology with equation of state

2019 ◽  
Vol 97 (7) ◽  
pp. 752-760 ◽  
Author(s):  
M. Farasat Shamir ◽  
Adnan Malik
Keyword(s):  
Equation Of State ◽  
Exact Solutions ◽  
Scalar Potential ◽  
State Parameter ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Radiation Universe ◽  
Modified Formula ◽  
Friedmann Robertson Walker ◽  
Dust Universe

The aim of this paper is to investigate the field equations of modified [Formula: see text] theory of gravity, where R and [Formula: see text] represent the Ricci scalar and scalar potential, respectively. We consider the Friedmann–Robertson–Walker space–time for finding some exact solutions by using different values of equation of state parameter. In this regard, different possibilities of the exact solutions have been discussed for dust universe, radiation universe, ultra-relativistic universe, sub-relativistic universe, stiff universe, and dark energy universe. Mainly power law and exponential forms of the scale factor are chosen for the analysis.

FRW viscous fluid cosmological model with time-dependent inhomogeneous equation of state

2017 ◽  
Vol 15 (01) ◽  
pp. 1830001 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Quadratic Form ◽  
State Parameter ◽  
The Other ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Viscous Models

In this paper, we present two viscous models of non-perfect fluid by avoiding the introduction of exotic dark energy. We consider the first model in terms of deceleration parameter [Formula: see text] has a viscosity of the form [Formula: see text] and the other model in quadratic form of [Formula: see text] of the type [Formula: see text]. In this framework we find the solutions of field equations by using inhomogeneous equation of state of form [Formula: see text] with equation of state parameter [Formula: see text] is constant and [Formula: see text].

scholarly journals GENERALIZED MODEL FOR Λ DARK ENERGY

2009 ◽  
Vol 18 (03) ◽  
pp. 389-396 ◽  
Author(s):  
UTPAL MUKHOPADHYAY ◽  
P. C. RAY ◽  
SAIBAL RAY ◽  
S. B. DUTTA CHOUDHURY
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
A Priori ◽  
State Parameter ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Two Fluid

Einstein field equations under spherically symmetric space–times are considered here in connection with dark energy investigation. A set of solutions is obtained for a kinematic Λ model, viz. [Formula: see text], without assuming any a priori value for the curvature constant and the equation-of-state parameter ω. Some interesting results, such as the nature of cosmic density Ω and deceleration parameter q, have been obtained with the consideration of two-fluid structure instead of the usual unifluid cosmological model.

Stability of anisotropic perturbed Einstein universe in f(R) gravity

2020 ◽  
Vol 35 (18) ◽  
pp. 2050152
Author(s):  
M. Sharif ◽  
Sana Saleem
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
State Parameter ◽  
Field Equations ◽  
Static Universe ◽  
Scale Factors ◽  
Static Solutions ◽  
Equation Of State Parameter ◽  
Specific Formula ◽  
Einstein Static Universe

The aim of this paper is to investigate the existence of stable modes of the Einstein static universe in the background of [Formula: see text] theory. For this purpose, we take homogeneous anisotropic perturbations in scale factors as well as matter contents. We construct static and perturbed field equations that are further parameterized by linear equation of state parameter. We obtain the Einstein static solutions for two specific [Formula: see text] models and graphically analyze their stable regions. It is concluded that contrary to general relativity, there exists stable Einstein static universe with anisotropic perturbations.

COSMOLOGY WITH NEGATIVE POTENTIALS WITH wϕ<-1

2004 ◽  
Vol 13 (09) ◽  
pp. 1939-1953 ◽  
Author(s):  
A. DE LA MACORRA ◽  
G. GERMÁN
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Scalar Potential ◽  
Energy Condition ◽  
State Parameter ◽  
Scalar Fields ◽  
High Energy ◽  
Equation Of State Parameter

We study the cosmology of canonically normalized scalar fields that lead to an equation of state parameter of wϕ=pϕ/ρϕ<-1 without violating the weak energy condition: ρ=Σiρi≥0 and ρi+pi≥0. This kind of behavior requires a negative scalar potential V, widely predicted in particle physics. We show that the energy density ρϕ=Ek+V takes negative values with an equation of state with wϕ<-1. However, the net effect of the ϕ field on the scale factor is to decelerate it giving a total equation of state parameter w=p/ρ>wb=pb/ρb, where ρb stands for any kind of energy density with -1≤wb≤1, such as radiation, matter, cosmological constant or other scalar field with a potential V≥0. The fact that ρϕ<0 allows, at least in principle, to have a small cosmological constant or quintessence today as the cancellation of high energy scales such as the electroweak or susy breaking scale. While V is negative |ρϕ| is smaller than the sum of all other energy densities regardless of the functional form of the potential V. We show that the existence of a negative potential leads, inevitable, to a collapsing universe, i.e. to a would be "big crunch." In this picture we would still be living in the expanding universe.

scholarly journals Tachyon field as a dark energy in Bianchi type-V spacetime

2015 ◽  
Vol 30 (01) ◽  
pp. 1550008 ◽  
Author(s):  
J. Sadeghi ◽  
H. Farahani
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Bianchi Type ◽  
Scalar Potential ◽  
State Parameter ◽  
Tachyon Field ◽  
Equation Of State Parameter ◽  
Type V ◽  
Bianchi Type V

In this paper, we consider Bianchi type-V spacetime and study a cosmological model of dark energy based on tachyon scalar field. We assumed three different kinds of matter without possibility of interaction with scalar dark energy. Assuming power law Hubble parameter in terms of scale factor we obtain evolution of scalar field, scalar potential and equation of state parameter.

scholarly journals The atmosphere of a black hole

2016 ◽  
Vol 31 (05) ◽  
pp. 1650034
Author(s):  
Metin Arik ◽  
Yorgo Senikoglu
Keyword(s):  
Black Hole ◽  
Equation Of State ◽  
State Parameter ◽  
Fluid Solution ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Special Case ◽  
Isotropic Fluid

We present a static, isotropic fluid solution around a black hole and its effects on the field equations and the horizon. We offer the solutions, their descriptions and we comment on their shortcomings. We derive from the proposed metric the density, the pressure, the equation of state, the temperature near and far of the black hole and the equation of state parameter. We show that for a special case, when [Formula: see text] the solution behaves as [Formula: see text], the equation of state for radiation and for [Formula: see text] we observe that [Formula: see text], the equation of state for dust.

Study of Tsallis, Rényi and Sharma–Mittal holographic dark energies for entropy corrected modified field equations in Hořava–Lifshitz gravity

2020 ◽  
Vol 17 (11) ◽  
pp. 2050170
Author(s):  
Sayani Maity ◽  
Ujjal Debnath
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Cold Dark Matter ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Frw Universe ◽  
Equation Of State Parameter ◽  
The Universe

The purpose of this work is to study the Tsallis, Rényi and Sharma–Mittal holographic dark energy models in order to evaluate the accelerated expansion of the Universe. In this regard, we consider the modified field equations for logarithmic and power law versions of entropy corrected models in FRW Universe filled with interacting dark energy and cold dark matter within the framework of Hořava–Lifshitz gravity. Employing the Nojiri and Odintsov (NO) cut-off as infrared cutoff, we explore the nature of the different cosmological quantities like the equation of state parameter, squared speed of sound and [Formula: see text]–[Formula: see text] cosmological plane during the cosmic evolution. The equation of state parameter shows the different stages of the evolution of the Universe for the considered models. By analyzing the cosmological plane [Formula: see text]–[Formula: see text], we obtain the freezing region for these models. Also, due to the study of squared speed of sound, we show the classically stable behavior of the considered models.

scholarly journals Anisotropic Universe in f(G,T) Gravity

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
M. Farasat Shamir
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Energy Momentum Tensor ◽  
State Parameter ◽  
Momentum Tensor ◽  
Anisotropic Universe ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Physical Quantities ◽  
Bonnet Term

This paper is devoted to investigating the recently introduced f(G,T) theory of gravity, where G is the Gauss-Bonnet term and T is the trace of the energy-momentum tensor. For this purpose, anisotropic background is chosen and a power law f(G,T) gravity model is used to find the exact solutions of field equations. In particular, a general solution is obtained which is further used to reconstruct some important solutions in cosmological contexts. The physical quantities like energy density, pressure, and equation of state parameter are calculated. A Starobinsky-like f2(T) model is proposed which is used to analyze the behavior of universe for different values of equation of state parameter. It is concluded that presence of term T in the bivariate function f(G,T) may give many cosmologically important solutions of the field equations.

Hypersurface-homogeneous cosmological models with dynamical equation of state parameter in Lyra geometry

2015 ◽  
Vol 93 (10) ◽  
pp. 1100-1105 ◽  
Author(s):  
Shri Ram ◽  
S. Chandel ◽  
M.K. Verma
Keyword(s):  
Dynamical Equation ◽  
State Parameter ◽  
Lyra Geometry ◽  
Cosmological Models ◽  
Anisotropic Fluid ◽  
Late Time ◽  
Field Equations ◽  
Homogeneous Cosmological Models ◽  
Negative Constant ◽  
Equation Of State Parameter

The hypersurface homogeneous cosmological models are investigated in the presence of an anisotropic fluid in the framework of Lyra geometry. Exact solutions of field equations are obtained by applying a special law of variation for mean Hubble parameter that gives a negative constant value of the deceleration parameter. These solutions correspond to anisotropic accelerated expanding cosmological models that isotropize for late time even in the presence of anisotropic fluid. The anisotropy of the fluid also isotropizes at late time. Some physical and kinematical properties of the model are also discussed.

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