scholarly journals FULL CAUSAL BULK VISCOUS COSMOLOGIES WITH TIME-VARYING CONSTANTS

2003 ◽  
Vol 12 (05) ◽  
pp. 861-883 ◽  
Author(s):  
JOSÉ ANTONIO BELINCHÓN ◽  
INDRAJIT CHAKRABARTY
Keyword(s):  
Equations Of State ◽  
Functional Dependence ◽  
Physical Parameters ◽  
Time Varying ◽  
Field Equations ◽  
Bulk Viscous ◽  
Varying Constants ◽  
Time Varying Constants ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

We study the evolution of a flat Friedmann–Robertson–Walker Universe, filled with a bulk viscous cosmological fluid, in the presence of time varying "constants." The dimensional analysis of the model suggests a proportionality between the bulk viscous pressure of the dissipative fluid and the energy density. Using this assumption and with the choice of the standard equations of state for the bulk viscosity coefficient, temperature and relaxation time, the general solution of the field equations can be obtained, with all physical parameters having a power-law time dependence. The symmetry analysis of this model, performed using Lie group techniques, confirms the uniqueness of the solution for this functional form of the bulk viscous pressure. In order to find another possible solution we relax the hypotheses and assume a concrete functional dependence for the "constants."

scholarly journals Cosmic Evolution of Viscous QCD Epoch in Causal Eckart Frame

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 112
Author(s):  
Eman Abdel Hakk ◽  
Abdel Nasser Tawfik ◽  
Afaf Nada ◽  
Hayam Yassin
Keyword(s):  
Energy Density ◽  
Energy Flow ◽  
Equations Of State ◽  
Temporal Evolution ◽  
Particle Diffusion ◽  
Cosmic Evolution ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure ◽  
Particle Current

It is conjectured that in cosmological applications the particle current is not modified but finite heat or energy flow. Therefore, comoving Eckart frame is a suitable choice, as it merely ceases the charge and particle diffusion and conserves charges and particles. The cosmic evolution of viscous hadron and parton epochs in casual and non-casual Eckart frame is analyzed. By proposing equations of state deduced from recent lattice QCD simulations including pressure p, energy density ρ, and temperature T, the Friedmann equations are solved. We introduce expressions for the temporal evolution of the Hubble parameter H˙, the cosmic energy density ρ˙, and the share η˙ and the bulk viscous coefficient ζ˙. We also suggest how the bulk viscous pressure Π could be related to H. We conclude that the relativistic theory of fluids, the Eckart frame, and the finite viscous coefficients play essential roles in the cosmic evolution, especially in the hadron and parton epochs.

BULK VISCOUS BRANS–DICKE COSMOLOGICAL MODELS AND LATE-TIME ACCELERATION OF THE UNIVERSE

2003 ◽  
Vol 12 (05) ◽  
pp. 925-939 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Energy Density ◽  
Momentum Tensor ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Bulk Viscous ◽  
Order Of Magnitude ◽  
Viscous Pressure ◽  
The Universe ◽  
Matter Energy

We consider the dynamics of a causal bulk viscous cosmological fluid filled flat homogeneous Universe in the framework of the Brans–Dicke theory. Three classes of exact solutions of the field equations are obtained and the behavior of the physical parameters is considered in detail. In this model the energy density associated to the Brans–Dicke scalar field is of the same order of magnitude as the matter energy density. The inclusion of the bulk viscous pressure term in the matter energy-momentum tensor leads to a non-decelerating evolution of the Universe.

scholarly journals PERFECT FLUID COSMOLOGICAL MODELS WITH TIME-VARYING CONSTANTS

2003 ◽  
Vol 12 (06) ◽  
pp. 1113-1129 ◽  
Author(s):  
JOSÉ ANTONIO BELINCHÓN ◽  
INDRAJIT CHAKRABARTY
Keyword(s):  
Cosmological Model ◽  
Perfect Fluid ◽  
Fluid Model ◽  
Time Varying ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
Varying Constants ◽  
Time Varying Constants ◽  
Limiting Case ◽  
Symmetry Method

In this paper, we study in detail a perfect fluid cosmological model with time-varying "constants" using dimensional analysis and the symmetry method. We examine the case of variable "constants" in detail without considering the perfect fluid model as a limiting case of a model with a causal bulk viscous fluid as discussed in a recent paper. We obtain some new solutions through the Lie method and show that when matter creation is considered, these solutions are physically relevant.

scholarly journals A THEORY OF TIME-VARYING CONSTANTS

2001 ◽  
Vol 10 (03) ◽  
pp. 299-309 ◽  
Author(s):  
JOSÉ ANTONIO BELINCHÓN ◽  
ANTONIO ALFONSO-FAUS
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Cosmological Model ◽  
Perfect Fluid ◽  
Gauge Invariance ◽  
Time Varying ◽  
Field Equations ◽  
Cosmological Time ◽  
Varying Constants ◽  
Time Varying Constants

We present a flat (K=0) cosmological model, described by a perfect fluid with the "constants" G, c and Λ varying with cosmological time t. We introduce Planck's "constant" ℏ in the field equations through the equation of state for the energy density of radiation. We then determine the behaviour of the "constants" by using the zero divergence of the second member of the modified Einstein's field equations i.e. div [Formula: see text], together with the equation of state and the Einstein cosmological equations. Assuming realistic physical and mathematical conditions we obtain a consistent result with ℏ c= constant . In this way we obtain gauge invariance for the Schrödinger equation and the behavior of the remaining "constants."

scholarly journals Iterative solutions for relativistic dissipative cosmologies

2002 ◽  
Vol 80 (5) ◽  
pp. 591-598
Author(s):  
T Harko ◽  
M K Mak
Keyword(s):  
Order Approximation ◽  
Pressure Ratio ◽  
Field Equations ◽  
Bulk Viscous Fluid ◽  
Gravitational Field Equations ◽  
Bulk Viscous ◽  
Iterative Solutions ◽  
Viscous Pressure ◽  
Thermodynamic Pressure ◽  
Bulk Viscous Pressure

Iterative solutions of the gravitational field equations for a homogeneous flat Friedmann–Robertson–Walker Universe filled with a causal bulk viscous fluid in the framework of the full Israel–Stewart–Hiscock theory are presented. The general solution of the field equations are presented in a parametric form in the zeroth-, first-, second-, and mth-order approximation by the method of iteration. The time evolution of the scale factor, energy density, deceleration parameter, entropy, Kretschmann scalar, and bulk viscous pressure-thermodynamic pressure ratio for a Zeldovich fluid-filled space-time are discussed. PACS Nos.: 98.80-k, 04.20Jb

scholarly journals Bianchi I in scalar and scalar-tensor cosmologies

Open Physics ◽  
2012 ◽  
Vol 10 (4) ◽  
Author(s):  
José Belinchón
Keyword(s):  
Perfect Fluid ◽  
Theoretical Models ◽  
Point Of View ◽  
Time Varying ◽  
Self Similarity ◽  
Bianchi I ◽  
Exact Power ◽  
Varying Constants ◽  
Time Varying Constants ◽  
Matter Fields

AbstractWe study how the constants G and Λ may vary in different theoretical models (general relativity (GR) with a perfect fluid, scalar cosmological models (SM) (“quintessence”) with and without interacting scalar and matter fields and three scalar-tensor theories (STT) with a dynamical Λ) in order to explain some observational results. We apply the program outlined in section II to study the Bianchi I models, under the self-similarity hypothesis. We put special emphasis on calculating exact power-law solutions which allow us to compare the different models. In all the studied cases we conclude that the solutions are isotropic and noninflationary. We also arrive at the conclusion that in the GR model with time-varying constants, Λ vanishes while G is constant. In the SM all the solutions are massless i.e. the potential vanishes and all the interacting models are inconsistent from the thermodynamical point of view. The solutions obtained in the STT collapse to the perfect fluid one obtained in the GR model where G is a true constant and Λ vanishes as in the GR and SM frameworks.

A comparative study of some cosmological models with time varying G and Λ: A symmetry approach

2019 ◽  
Vol 97 (10) ◽  
pp. 1083-1095 ◽  
Author(s):  
José Antonio Belinchón ◽  
Rafael Uribe
Keyword(s):  
Theoretical Models ◽  
Time Varying ◽  
Symmetry Approach ◽  
Exact Power ◽  
Walker Metric ◽  
Self Similar ◽  
Varying Constants ◽  
Time Varying Constants ◽  
Matter Collineation ◽  
Friedmann Robertson Walker

We study how the constants G and Λ may vary in four different theoretical models: general relativity with time-varying constants (Y.-K. Lau. Aust. J. Phys. 38, 547 (1985). doi: 10.1071/PH850547 ), the model proposed by Lu et al. (Phys Rev D, 89, 063526 (2014). doi: 10.1103/PhysRevD.89.063526 ), the model proposed by Bonanno et al. (Class. Quant. Grav. 24, 1443 (2007). doi: 10.1088/0264-9381/24/6/005 ), and the Brans–Dicke model with Λ([Formula: see text]) [ 25 ]. To carry out this study, we work under the self-similar hypothesis and we assume the same metric, a flat Friedmann–Robertson–Walker metric, and the same matter source, a perfect fluid. We put special emphasis on mathematical and formal aspects, which allows us to calculate exact power-law solutions through symmetry methods, matter collineation, and Noether symmetries. This enables us to compare the solutions of each model and in the same way to contrast the results with some observational data.

GENERALIZED SCALAR TENSOR THEORY IN FOUR AND HIGHER DIMENSION

2000 ◽  
Vol 09 (05) ◽  
pp. 543-549 ◽  
Author(s):  
SUBENOY CHAKRABORTY ◽  
ARABINDA GHOSH
Keyword(s):  
Physical Parameters ◽  
Scalar Tensor Theory ◽  
Higher Dimension ◽  
Field Equations ◽  
Bianchi I ◽  
Bulk Viscous Fluid ◽  
Tensor Theory ◽  
Bulk Viscous ◽  
Coupled Field ◽  
Coupled Field Equations

In this paper, we have considered generalized scalar–tensor theory for four-dimensional Bianchi-I model and also for a five-dimensional cosmological model. We have studied both exponential and power law solutions, considering a bulk viscous fluid. To solve the complicated coupled field equations, we have made assumptions among the physical parameters and solutions have been discussed.

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