scholarly journals Cosmological Particle Production and Causal Thermodynamics

1999 ◽  
Vol 52 (4) ◽  
pp. 659 ◽  
Author(s):  
M. K. Mak ◽  
T. Harko
Keyword(s):  
Particle Production ◽  
Particle Creation ◽  
Phenomenological Theory ◽  
Physical Parameters ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Inflationary Phase ◽  
Bulk Viscous ◽  
Minkowskian Geometry ◽  
The Universe

The full linear causal Israel–Stewart–Hiscock theory of bulk viscous processes in relativistic cosmological fluids is reformulated as an effective phenomenological theory for describing particle production processes in the early universe. Explicit expressions for the particle balance law and particle production rates are obtained that relate the particle creation rate to the bulk viscous (creation) pressure. The general formalism is applied to the case of a full causal cosmological fluid with bulk viscosity coecient proportional to the Hubble function. In this case the general solution of the gravitational field equations can be expressed in an exact parametric form. For an appropriate choice of the physical parameters, the dynamics of the universe can be modelled as starting from a vacuum quasi-Minkowskian geometry, followed by an inflationary period but ending in a non-inflationary phase. The influence of the matter creation processes on the evolution of the universe and the behaviour of the energy density, temperature and entropy are investigated.

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 Bulk viscous quintessential inflation

2018 ◽  
Vol 27 (05) ◽  
pp. 1850052 ◽  
Author(s):  
Jaume Haro ◽  
Supriya Pan
Keyword(s):  
General Relativity ◽  
Particle Production ◽  
Cosmic Acceleration ◽  
Inflationary Universe ◽  
De Sitter ◽  
Thermodynamical Equilibrium ◽  
One Dimensional ◽  
Inflationary Phase ◽  
Bulk Viscous ◽  
The Universe

In a spatially-flat Friedmann–Lemaître–Robertson–Walker universe, the incorporation of bulk viscous process in general relativity leads to an appearance of a nonsingular background of the universe that both at early and late times depicts an accelerated universe. These early and late scenarios of the universe can be analytically calculated and mimicked, in the context of general relativity, by a single scalar field whose potential could also be obtained analytically where the early inflationary phase is described by a one-dimensional Higgs potential and the current acceleration is realized by an exponential potential. We show that the early inflationary universe leads to a power spectrum of the cosmological perturbations which match with current observational data, and after leaving the inflationary phase, the universe suffers a phase transition needed to explain the reheating of the universe via gravitational particle production. Furthermore, we find that at late times, the universe enters into the de Sitter phase that can explain the current cosmic acceleration. Finally, we also find that such bulk viscous-dominated universe attains the thermodynamical equilibrium, but in an asymptotic manner.

Cosmology of string bulk viscosity in f(G) theory of gravitation

2018 ◽  
Vol 15 (07) ◽  
pp. 1850116 ◽  
Author(s):  
S. D. Katore ◽  
S. P. Hatkar ◽  
S. V. Gore
Keyword(s):  
Large Time ◽  
Bianchi Type ◽  
String Model ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Bulk Viscous ◽  
Theory Of Gravitation ◽  
Modified Formula ◽  
The Universe

LRS Bianchi type I space time is considered to explore bulk viscous string model in modified [Formula: see text] gravity. Field equations are solved with some physically viable condition. It is observed that the string phase of the universe disappears. The Gauss–Bonnet invariant significantly effects on galactic fluid. The universe is expanding and isotropic at large time. Some physical parameters are also discussed in detail.

scholarly journals Physical Acceptability of the Renyi, Tsallis and Sharma-Mittal Holographic Dark Energy Models in the f(T,B) Gravity under Hubble’s Cutoff

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 67
Author(s):  
Salim Harun Shekh ◽  
Pedro H. R. S. Moraes ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Two Fluids ◽  
Gravitational Field Equations ◽  
Energy Models ◽  
Different Types ◽  
The Universe

In the present article, we investigate the physical acceptability of the spatially homogeneous and isotropic Friedmann–Lemâitre–Robertson–Walker line element filled with two fluids, with the first being pressureless matter and the second being different types of holographic dark energy. This geometric and material content is considered within the gravitational field equations of the f(T,B) (where T is the torsion scalar and the B is the boundary term) gravity in Hubble’s cut-off. The cosmological parameters, such as the Equation of State (EoS) parameter, during the cosmic evolution, are calculated. The models are stable throughout the universe expansion. The region in which the model is presented is dependent on the real parameter δ of holographic dark energies. For all δ≥4.5, the models vary from ΛCDM era to the quintessence era.

scholarly journals Accelerating Universe with Viscous Cosmic String in Quadratic Form of Teleparallel Gravity

2019 ◽  
Vol 11 (3) ◽  
pp. 249-262
Author(s):  
S. R. Bhoyar ◽  
V. R. Chirde ◽  
S. H. Shekh
Keyword(s):  
Cosmic String ◽  
Teleparallel Gravity ◽  
Negative Slope ◽  
Accelerating Universe ◽  
Field Equations ◽  
Physical Behavior ◽  
Torsion Scalar ◽  
Bulk Viscous ◽  
The Universe ◽  
Physical Quantities

In this paper, we have investigated Kantowaski-Sachs cosmological model with bulk viscous and cosmic string in the framework of Teleparallel Gravity so called f(T) gravity, where T denotes the torsion scalar. The behavior of accelerating universe is discussed towards the particular choice of f(T) = Α(T) + β(T)m. The exact solutions of the field equations are obtained by applying variable deceleration parameter which is linear in time with a negative slope. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the torsion scalar for the universe is evaluated.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
Author(s):  
P.K. SAHOO ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

A five dimensional Kaluza-Klein space time is considered with wet dark fluid (WDF) source in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D \textbf{84}, 024020, (2011)). A new equation of state in the form of WDF has been used for dark energy (DE) component of the universe. It is modeled on the equation of state p=\omega(\rho-\rho^*) which can be describing a liquid, for example water. The exact solutions to the corresponding field equations are obtained for power law and exponential law of the volumetric expansion. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and the very late time of the universe. This model obtained here shows that even in the presence of wet dark fluid, the universe indicates accelerated expansion of the universe.

Kaluza–Klein dark energy model in the form of wet dark fluid in f(R, T) gravity

2014 ◽  
Vol 92 (9) ◽  
pp. 1062-1067 ◽  
Author(s):  
P. K. Sahoo ◽  
B. Mishra
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Dark Fluid ◽  
The Universe ◽  
Kaluza Klein

In this paper, we have investigated the five-dimensional Kaluza–Klein space time with wet dark fluid (WDF), which is a candidate for dark energy (DE), in the framework of f(R, T) gravity. R and T denote the Ricci scalar and the trace of the energy–momentum tensor, respectively (Harko et al. Phys. Rev. D, 84, 024020 (2011)). We have used equation of state in the form of WDF for the DE component of the universe. It is modeled on the equation of state p = ω(ρ – ρ*). With the help of the power law and exponential law of volumetric expansion, we have derived the exact solutions of the corresponding field equations. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and very late time of the universe. It is concluded that the model obtained here shows that even in the presence of WDF, the universe indicates accelerated expansion of the universe.

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 Viscous cosmology in the Weyl-type f(Q, T) gravity

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Gaurav N. Gadbail ◽  
Simran Arora ◽  
P. K. Sahoo
Keyword(s):  
Bulk Viscosity ◽  
Viscosity Coefficient ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Bulk Viscous ◽  
The Impact ◽  
Bulk Viscosity Coefficient ◽  
The Universe

AbstractBulk viscosity is the only viscous influence that can change the background dynamics in a homogeneous and isotropic universe. In the present work, we analyze the bulk viscous cosmological model with the bulk viscosity coefficient of the form $$\zeta =\zeta _0+\zeta _1H+\zeta _2\left( \frac{\dot{H}}{H}+H\right) $$ ζ = ζ 0 + ζ 1 H + ζ 2 H ˙ H + H where, $$\zeta _0$$ ζ 0 , $$\zeta _1$$ ζ 1 and $$\zeta _2$$ ζ 2 are bulk viscous parameters, and H is the Hubble parameter. We investigate the impact of the bulk viscous parameter on dynamics of the universe in the recently proposed Weyl-type f(Q, T) gravity, where Q is the non-metricity, and T is the trace of the matter energy–momentum tensor. The exact solutions to the corresponding field equations are obtained with the viscous fluid and the linear model of the form $$f(Q, T)=\alpha Q+\frac{\beta }{6\kappa ^2}T$$ f ( Q , T ) = α Q + β 6 κ 2 T , where $$\alpha $$ α and $$\beta $$ β are model parameters. Further, we constrain the model parameters using the 57 points Hubble dataset the recently released 1048 points Pantheon sample and the combination Hz + BAO + Pantheon, which shows our model is good congeniality with observations. We study the possible scenarios and the evolution of the universe through the deceleration parameter, the equation of state (EoS) parameter, the statefinder diagnostics, and the Om diagnostics. It is observed that the universe exhibits a transition from a decelerated to an accelerated phase of the universe under certain constraints of model parameters.

Particle creation in FLRW higher dimensional universe with gravitational and cosmological constants

2021 ◽  
Author(s):  
Archana Dixit ◽  
Priyanka Garg ◽  
Anirudh Pradhan
Keyword(s):  
Gravitational Constant ◽  
Particle Creation ◽  
Physical Parameters ◽  
Distance Modulus ◽  
Field Equations ◽  
Gravitational And Cosmological Constants ◽  
Higher Dimensional ◽  
Age Of The Universe ◽  
The Look ◽  
Generation Mechanisms

We study the mechanism of particle creation in the higher dimensional FLRW type cosmological models by using variable cosmological and gravitational constants. The solution of the corresponding field equations is obtained by assuming a linear function of the Hubble parameter (H), i.e., q = α + βH [Dixit et al., Pramana: 94, 25 (2020)] which gives a scale factor a(t) = exp({\frac{1}{\beta}\sqrt{2\beta t +k} }), where k and β are positive constants. Here we consider the time-dependent higher-dimensional (HD) field equations, including the general formulation of particle creation (PC) and entropy generation mechanisms (EGM). We also investigate few quantities such as the deceleration parameter (DP) q, particle creation rate \psi, the entropy S, the cosmological constant (CC) /Lambda, Newton's gravitational constant (GC) G, the energy density (ED) ρ and discuss their physical significance. We have observed that all quantities, except the gravitational constant (G) and the entropy (S), decrease with time in all dimensions characteristically. However, the entropy S and the gravitational constant G increase with time. Additionally, we have also discussed the look-back time, luminosity distance, distance modulus and age of the universe with redshift z and observed the role of particle formation in universe evolution in early and late times. For the derived model, we have calculated various physical parameters, which are in good agreement with the recent observations.

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