Dark energy and viscous cosmology with variable G and Λ in an anisotropic background

2013 ◽  
Vol 91 (2) ◽  
pp. 153-157 ◽  
Author(s):  
V. Fayaz ◽  
M.R. Setare ◽  
H. Hossienkhani
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Bulk Viscosity ◽  
Deceleration Parameter ◽  
Chaplygin Gas ◽  
Density Parameter ◽  
Type I ◽  
De Sitter ◽  
Variable G And Λ ◽  
Variable G

The general Bianchi type I with dark energy in the form of standard and modified Chaplygin gas with variable G and Λ and bulk viscosity have been investigated. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models that reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe, that which yields a constant value for the deceleration parameter. We reconstruct bulk viscosity, ξ, gravitational parameter, G, cosmological term, Λ, density parameter, Ω, cosmological constant density parameter, ΩΛ, and deceleration parameter, q, for different equations of state. In the large time limit the model describes an accelerating universe wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

scholarly journals Diagnostics for generalized power-law torsion–matter coupling f(T) model

2019 ◽  
Vol 28 (02) ◽  
pp. 1950031
Author(s):  
Rui-Hui Lin ◽  
Qiang Wen ◽  
Xiang-Hua Zhai ◽  
Xin-Zhou Li
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
System Analysis ◽  
Coupling Model ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Matter Coupling ◽  
Energy Models ◽  
The Universe

The currently accelerated expansion of our universe is unarguably one of the most intriguing problems in today’s physics research. Two realistic nonminimal torsion–matter coupling [Formula: see text] models have been established and studied in our previous papers [C. J. Feng, F. F. Ge, X. Z. Li, R. H. Lin and X. H. Zhai, Phys. Rev. D 92 (2015) 104038; R. H. Lin, X. H. Zhai and X. Z. Li, Eur. Phys. J. C 77 (2017) 504] aiming to explain this “dark energy” problem. In this paper, we study the generalized power-law torsion–matter coupling [Formula: see text] model. Dynamical system analysis shows that the three expansion phases of the universe, i.e. the radiation-dominated era, the matter-dominated era and the dark energy-dominated era, can all be reproduced in this generalized model. By using the statefinder and [Formula: see text] diagnostics, we find that the different cases of the model can be distinguished from each other and from other dark energy models such as the two models in our previous papers, [Formula: see text]CDM, quintessence and Chaplygin gas. Furthermore, the analyses also show that all kinds of generalized power-law torsion–matter coupling model are able to cross the [Formula: see text] divide from below to above, which is a realization of quintom scenario. The decrease of the energy density resulting from the crossing of [Formula: see text] will make the catastrophic fate of the universe avoided and a de Sitter expansion fate in the future will be approached.

BULK VISCOUS ANISOTROPIC COSMOLOGICAL MODELS WITH VARIABLE G AND Λ

2002 ◽  
Vol 11 (06) ◽  
pp. 893-912 ◽  
Author(s):  
ANIRUDH PRADHAN ◽  
VINOD KUMAR YADAV
Keyword(s):  
Power Law ◽  
Bulk Viscosity ◽  
Bianchi Type ◽  
Einstein Field Equations ◽  
Variable G And Λ ◽  
Field Equations ◽  
Expansion Factor ◽  
Bulk Viscous ◽  
Suitable Power ◽  
Variable G

The Einstein field equations with bulk viscosity and variable G and Λ for Bianchi-type universes are studied under the assumption of a power-law time variation of the expansion factor, achieved via a suitable power-law assumption for the Hubble parameter suggested by M. S. Berman. All the models have a power-law variation of pressure and density and are singular at the epoch t = 0. The variation of G(t) as [Formula: see text] and Λ(t) as [Formula: see text] is consistent with these models.

scholarly journals Cosmological singularities in interacting dark energy models with an ω(q) parametrization

2019 ◽  
Vol 28 (01) ◽  
pp. 1950019 ◽  
Author(s):  
Emilio Elizalde ◽  
Martiros Khurshudyan ◽  
Shin’ichi Nojiri
Keyword(s):  
Dark Energy ◽  
Energy Budget ◽  
Deceleration Parameter ◽  
Finite Time ◽  
Numerical Solutions ◽  
Unstable State ◽  
Stable Node ◽  
Type I ◽  
Cosmological Singularity ◽  
Time Future

Future singularities arising in a family of models for the expanding universe, characterized by sharing a convenient parametrization of the energy budget in terms of the deceleration parameter, are classified. Finite-time future singularities are known to appear in many cosmological scenarios, in particular, in the presence of viscosity or nongravitational interactions, the last being known to be able to suppress or just change in some cases the type of the cosmological singularity. Here, a family of models with a parametrization of the energy budget in terms of the deceleration parameter are studied in the light of Gaussian processes using reconstructed data from [Formula: see text]-value [Formula: see text] datasets. Eventually, the form of the possible nongravitational interaction between dark energy and dark matter is constructed from these smoothed [Formula: see text] data. Using phase space analysis, it is shown that a noninteracting model with dark energy [Formula: see text] ([Formula: see text] being the deceleration parameter) may evolve, after starting from a matter-dominated unstable state, into a de Sitter universe (the solution being in fact a stable node). Moreover, for a model with interaction term [Formula: see text] ([Formula: see text] is a parameter and [Formula: see text], the Hubble constant) three stable critical points are obtained, which may have important astrophysical implications. In addition, part of the paper is devoted to a general discussion of the finite-time future singularities obtained from direct numerical integration of the field equations, since they appear in many cosmological scenarios and could be useful for future extended studies of the models here introduced. Numerical solutions for the new models, produce finite-time future singularities of Type I or Type III, or an [Formula: see text]-singularity, provided general relativity describes the background dynamics.

scholarly journals DARK ENERGY IN GLOBAL BRANE UNIVERSE

2007 ◽  
Vol 16 (10) ◽  
pp. 1633-1640 ◽  
Author(s):  
YONGLI PING ◽  
LIXIN XU ◽  
CHENGWU ZHANG ◽  
HONGYA LIU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Exact Solutions ◽  
Deceleration Parameter ◽  
Mass Density ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Friedmann Equations

We discuss the exact solutions of brane universes and the results indicate that the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain that the new term varies with the redshift z. Finally, the evolutions of the mass density parameter Ω2, dark energy density parameter Ωx and deceleration parameter q2 are studied.

VISCOUS GENERALIZED CHAPLYGIN GAS

2006 ◽  
Vol 15 (08) ◽  
pp. 1151-1161 ◽  
Author(s):  
XIANG-HUA ZHAI ◽  
YOU-DONG XU ◽  
XIN-ZHOU LI
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Critical Energy ◽  
State Equation ◽  
Chaplygin Gas ◽  
Point Of View ◽  
Dynamical Analysis ◽  
Density Parameter ◽  
Generalized Chaplygin Gas ◽  
Barotropic Fluid

Viscous generalized Chaplygin gas (GCG) cosmology is discussed, assuming that there is bulk viscosity in the linear barotropic fluid and GCG. wγ = γ - 1 and wg represent the state equation parameters for barotropic fluid and GCG, respectively, in which γ = 1 or [Formula: see text] corresponds to ordinary matter or radiation. The dynamical analysis indicates that the phase [Formula: see text] is a dynamical attractor and the equation of state of GCG approaches it from either wg > -1 or wg < -1 depending on the choice of its initial cosmic density parameter and the ratio of pressure to critical energy density, where τg and τγ are viscosity parameters. Therefore, the equation of state wg will cross the boundary wg = -1 if we choose initial value wg < -1. Furthermore, we show that bulk viscosity coefficients should satisfy inequalities from the point of view of dynamics.

scholarly journals Origin of Universe accelerated expansion and prediction of the right deceleration parameter

2019 ◽  
Author(s):  
Paolo Di Sia
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Ad Hoc ◽  
Accelerated Expansion ◽  
Dense Layer ◽  
De Sitter ◽  
Dark Energy Density ◽  
Particle Velocities ◽  
De Sitter Universe ◽  
The Right

The filament (f) theory implies initial isotropic particle-velocities with uniform value-distribution between zero and the speed of light c. That leads to a universe boundary coinciding with the events horizon of its centre. The very dense layer of particles and antiparticles expanding with almost c observed at retarded times attracts the internal particles thus implying for them an accelerated expansion. There is no need for an "ad hoc" dark energy implying repulsion. The predicted negative deceleration parameter q corresponds to a dark energy density 95.5 % of the critical value. If the red-shift of far galaxies was due to the only Doppler-Fizeau effect, the standard value 73 % is obtained. The past and future q is predicted. The q value was a negative maximum just after the primordial annihilation of the particles with the antiparticles and will vanish at about 3TH (where TH denotes the Hubble time) after the present time t. For t larger than 3TH, it will be positive, tending to 1/2, typical of the Einstein-De Sitter universe.

scholarly journals LRS Bianchi Type-I Cosmological Model with Anisotropic Dark Energy and Special Form of Deceleration Parameter

2013 ◽  
Vol 04 (08) ◽  
pp. 1037-1040 ◽  
Author(s):  
Kishor Shankarrao Adhav ◽  
Rajesh Purushottam Wankhade ◽  
Abhijit Shankarrao Bansod
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Deceleration Parameter ◽  
Special Form ◽  
Bianchi Type ◽  
Type I ◽  
Bianchi Type I ◽  
Anisotropic Dark Energy
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