scholarly journals Will There Be Future Deceleration? A Study of Particle Creation Mechanism in Nonequilibrium Thermodynamics

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Supriya Pan ◽  
Subenoy Chakraborty
Keyword(s):  
Production Rate ◽  
Deceleration Parameter ◽  
Particle Production ◽  
Nonequilibrium Thermodynamics ◽  
Particle Creation ◽  
Point Of View ◽  
Late Time ◽  
Cosmological Solutions ◽  
Alternative Choice ◽  
The Universe

The paper deals with nonequilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe. Using Friedmann’s equations, it is shown that the deceleration parameter (q) can be obtained from the knowledge of the particle production rate (Γ). Motivated by thermodynamical point of view, cosmological solutions are evaluated for the particle creation rates in three cosmic phases, namely, inflation, matter dominated era, and present late time acceleration. The deceleration parameter (q) is expressed as a function of the redshift parameter (z), and its variation is presented graphically. Also, statefinder analysis has been presented graphically in three different phases of the universe. Finally, two noninteracting fluids with different particle creation rates are considered as cosmic substratum, and deceleration parameter (q) is evaluated. Whether more than one transition ofqis possible or not is examined by graphical representations.

scholarly journals COSMOLOGICAL BACKREACTION OF HEAVY STRING STATES

2011 ◽  
Vol 26 (35) ◽  
pp. 2615-2626
Author(s):  
G. DE RISI
Keyword(s):  
Phase Space ◽  
Particle Production ◽  
Numerical Solutions ◽  
Particle Creation ◽  
Big Bang ◽  
Smooth Transition ◽  
Massive String ◽  
Evolution Of The Universe ◽  
Scale Particle ◽  
The Universe

We propose a mechanism to have a smooth transition from a pre-Big Bang phase to a standard cosmological phase. Such transition is driven by gravitational production of heavy massive string states that backreact on the geometry to stop the growth of the curvature. Close to the string scale, particle creation can become effective because the string phase space compensate the exponential suppression of the particle production. Numerical solutions for the evolution of the Universe with this source are presented.

Cosmological model with variable deceleration parameter in f(R,T) modified gravity

2018 ◽  
Vol 15 (07) ◽  
pp. 1850115 ◽  
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Bhupendra Shukla
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Deceleration Parameter ◽  
Late Time ◽  
Type I ◽  
Field Equations ◽  
Geometrical Properties ◽  
Deceleration Phase ◽  
Modified Gravity Theory ◽  
The Universe

A study is made of the LRS Bianchi type-I cosmological model in [Formula: see text] modified gravity theory. Einstein’s field equations in [Formula: see text] gravity are solved by taking [Formula: see text] and the deceleration parameter [Formula: see text] to be a linear function of the Hubble parameter [Formula: see text]. The universe begins with an initial singular state and changes with time from an early deceleration phase to a late time acceleration phase. We have found that the jerk parameter [Formula: see text] in the model approaches that of the [Formula: see text] model at late times. We also discuss the physical and geometrical properties of the model.

Time-varying q-deformed dark energy interacts with dark matter

2017 ◽  
Vol 27 (01) ◽  
pp. 1750177
Author(s):  
Emre Dil ◽  
Erdinç Kolay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Particle Creation ◽  
State Parameter ◽  
Late Time ◽  
Dynamical Structure ◽  
Stable Attractor ◽  
Energy Quantum ◽  
The Universe

We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a [Formula: see text]-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume that the number of particles in each mode of the [Formula: see text]-deformed scalar field varies in time by the particle creation and annihilation. We first describe the [Formula: see text]-deformed scalar field dark energy quantum-field theoretically, then construct the action and the dynamical structure of these interacting dark sectors, in order to study the dynamics of the model. We perform the phase space analysis of the model to confirm and interpret our proposal by searching the stable attractor solutions implying the late-time accelerating phase of the universe. We then obtain the result that when interaction and equation-of-state parameter of the dark matter evolve from the present day values into a particular value, the dark energy turns out to be a [Formula: see text]-deformed scalar field.

scholarly journals Viscous cosmology for early- and late-time universe

2017 ◽  
Vol 26 (14) ◽  
pp. 1730024 ◽  
Author(s):  
Iver Brevik ◽  
Øyvind Grøn ◽  
Jaume de Haro ◽  
Sergei D. Odintsov ◽  
Emmanuel N. Saridakis
Keyword(s):  
Hubble Parameter ◽  
Equations Of State ◽  
Point Of View ◽  
Late Time ◽  
Macroscopic Theory ◽  
Viscous Cosmology ◽  
Phantom Divide ◽  
Special Cases ◽  
Ultimate Fate ◽  
The Universe

From a hydrodynamicist’s point of view the inclusion of viscosity concepts in the macroscopic theory of the cosmic fluid would appear most natural, as an ideal fluid is after all an abstraction (exluding special cases such as superconductivity). Making use of modern observational results for the Hubble parameter plus standard Friedmann formalism, we may extrapolate the description of the universe back in time up to the inflationary era, or we may go to the opposite extreme and analyze the probable ultimate fate of the universe. In this review, we discuss a variety of topics in cosmology when it is enlarged in order to contain a bulk viscosity. Various forms of this viscosity, when expressed in terms of the fluid density or the Hubble parameter, are discussed. Furthermore, we consider homogeneous as well as inhomogeneous equations of state. We investigate viscous cosmology in the early universe, examining the viscosity effects on the various inflationary observables. Additionally, we study viscous cosmology in the late universe, containing current acceleration and the possible future singularities, and we investigate how one may even unify inflationary and late-time acceleration. Finally, we analyze the viscosity-induced crossing through the quintessence-phantom divide, we examine the realization of viscosity-driven cosmological bounces, and we briefly discuss how the Cardy–Verlinde formula is affected by viscosity.

scholarly journals Creation of particles in a cyclic universe driven by loop quantum cosmology

2015 ◽  
Vol 24 (08) ◽  
pp. 1550062 ◽  
Author(s):  
Yaser Tavakoli ◽  
Júlio C. Fabris
Keyword(s):  
Scalar Field ◽  
Quantum Cosmology ◽  
Particle Production ◽  
Friedmann Equation ◽  
Big Bang ◽  
Loop Quantum Cosmology ◽  
Late Time ◽  
Background Density ◽  
The Future ◽  
The Universe

We consider an isotropic and homogeneous universe in loop quantum cosmology (LQC). We assume that the matter content of the universe is dominated by dust matter in early time and a phantom matter at late time which constitutes the dark energy component. The quantum gravity modifications to the Friedmann equation in this model indicate that the classical big bang singularity and the future big rip singularity are resolved and are replaced by quantum bounce. It turns out that the big bounce and recollapse in the herein model contribute to a cyclic scenario for the universe. We then study the quantum theory of a massive, nonminimally coupled scalar field undergoing cosmological evolution from primordial bounce towards the late time bounce. In particular, we solve the Klein–Gordon equation for the scalar field in the primordial and late time regions, in order to investigate particle production phenomena at late time. By computing the energy density of created particles at late time, we show that this density is negligible in comparison to the quantum background density at Planck era. This indicates that the effects of quantum particle production do not influence the future bounce.

scholarly journals Reconstruction of some cosmological models from the deceleration parameter

2021 ◽  
Vol 2081 (1) ◽  
pp. 012001
Author(s):  
Aroonkumar Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Particle Physics ◽  
Unsolved Problem ◽  
Gravity Models ◽  
Reasonable Assumption ◽  
Late Time ◽  
The Past ◽  
Acceleration Of The Universe ◽  
The Universe

Abstract Since the discovery of the late-time acceleration of the universe, researchers are still trying to fnd an explanation for it. This is regarded as the most important unsolved problem in cosmology today. The most favoured explanation is dark energy, an unknown or exotic form of matter with negative pressure. One may argue that particle physics may provide the answer in time. Currently, the LambdaCDM model is regarded as the best model. Although this model is reasonably successful and widely accepted, there is growing interest in looking at alternatives. Some of the reasons for this are the fne-tuning, coincidence, infationary paradigm and cosmological constant problems, and whether general relativity is valid on large scales. One focus in trying to understand dark energy is to assume some form of the scale, Hubble or deceleration parameter (or some other reasonable assumption), and then to see how well the model fts in with current observations. This approach is broadly called reconstruction. In this talk, we focus on the deceleration parameter. We provide a brief review of the various forms of the deceleration parameter that have been employed in the past in cosmology, and then focus on some particular forms of interest which have drawn some attention. We note that it is most worthwhile to study alternative dark energy and dark gravity models in order to fully understand the entire space of possibilities.

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.

Scalar-Gauss–Bonnet gravity and cosmic acceleration: Comparison with quintessence dark energy

2017 ◽  
Vol 26 (02) ◽  
pp. 1750008 ◽  
Author(s):  
M. Heydari-Fard ◽  
H. Razmi ◽  
M. Yousefi
Keyword(s):  
Energy Density ◽  
Deceleration Parameter ◽  
Coupling Parameter ◽  
Density Ratio ◽  
Cosmic Acceleration ◽  
Field Energy ◽  
Late Time ◽  
Deceleration Phase ◽  
Quintessence Field ◽  
The Universe

The late-time cosmic acceleration of the universe is explained in the framework of the Einstein-scalar-Gauss–Bonnet (GB) theory by considering different appropriate forms for the GB coupling parameter and the scalar field. The physical quantities such as the potential energy, the GB coupling parameter, the energy density, the pressure and the deceleration parameter are obtained in an exact parametric form of the volume scale factor of the universe. The behavior of the deceleration parameter shows a transition from the deceleration phase to the acceleration phase at the late times in agreement with the observational data. Finally, the GB energy density ratio is compared to the matter energy density and the scalar (the quintessence) field energy density in the early and late times.

scholarly journals QUANTUM EFFECTS FROM PARTICLE PRODUCTION ON BACKGROUND EVOLUTION AND CARDY–VERLINDE FORMULA IN f(R) GRAVITY

2011 ◽  
Vol 20 (13) ◽  
pp. 2449-2469 ◽  
Author(s):  
M. J. S. HOUNDJO ◽  
A. V. MONWANOU ◽  
JEAN B. CHABI OROU
Keyword(s):  
Particle Production ◽  
Space Dimension ◽  
Particle Creation ◽  
Quantum Effects ◽  
Dark Fluid ◽  
Verlinde Formula ◽  
Big Rip ◽  
The Universe ◽  
Entropy Of The Universe ◽  
Constant Dark

We investigate particle production in an expanding universe under the assumption that the Lagrangian contains the Einstein term R plus a modified gravity term of the form Rα, where α is a constant. Dark fluid is considered as the main content of the universe and the big rip singularity appears. Quantum effects due to particle creation is analyzed near the singularity and we find that for α ∈ ]½, 1[, quantum effects are dominant and the big rip may be avoided whereas for α ∈ J the dark fluid is dominant and the singularity remains. The Cardy–Verlinde formula is also introduced and its equivalence with the total entropy of the universe is checked. It is found that this can always occur in Einstein gravity while in f(R) gravity, it holds only for [Formula: see text], n being the space dimension, corresponding to the situation in which the big rip cannot be avoided.

Early inflation to late-time acceleration in f(G) model

2016 ◽  
Vol 31 (33) ◽  
pp. 1650187
Author(s):  
Malay Krishna Dutta ◽  
Kaushik Sarkar ◽  
B. Modak
Keyword(s):  
Ideal Fluid ◽  
Deceleration Parameter ◽  
Accelerating Universe ◽  
Late Time ◽  
Evolution Of The Universe ◽  
Late Time Acceleration ◽  
Modified Theory Of Gravity ◽  
Theory Of Gravity ◽  
The Universe ◽  
Modified Theory

We present some solutions in Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime in the modified theory of gravity with a general Gauss–Bonnet (GB) term f(G) and R2 including an ideal fluid. We present evolution of the universe introducing an ansatz without a prior choice of f(G) in one approach, while in other class of model, the solutions are obtained assuming few simple forms of f(G). Some of the solutions show early inflationary expansion, further in one solution the fluctuation of the deceleration parameter q is evident at the end of inflation. In all cases, late-time transition to accelerating universe at redshift z [Formula: see text] 0.7 is realizable.

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