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 Chameleon field dynamics during inflation

2018 ◽  
Vol 27 (04) ◽  
pp. 1850041 ◽  
Author(s):  
Nasim Saba ◽  
Mehrdad Farhoudi
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Big Bang ◽  
Late Time ◽  
Inflationary Model ◽  
Slow Roll ◽  
Equation Of State Parameter ◽  
The Common ◽  
The Universe

By studying the chameleon model during inflation, we investigate whether it can be a successful inflationary model, wherein we employ the common typical potential usually used in the literature. Thus, in the context of the slow-roll approximations, we obtain the e-folding number for the model to verify the ability of resolving the problems of standard big bang cosmology. Meanwhile, we apply the constraints on the form of the chosen potential and also on the equation of state parameter coupled to the scalar field. However, the results of the present analysis show that there is not much chance of having the chameleonic inflation. Hence, we suggest that if through some mechanism the chameleon model can be reduced to the standard inflationary model, then it may cover the whole era of the universe from the inflation up to the late time.

scholarly journals EMERGENT UNIVERSE WITH EXOTIC MATTER IN LOOP QUANTUM COSMOLOGY, DGP BRANE-WORLD AND KALUZA–KLEIN COSMOLOGY

2012 ◽  
Vol 27 (33) ◽  
pp. 1250189 ◽  
Author(s):  
PRABIR RUDRA
Keyword(s):  
Scalar Field ◽  
Quantum Cosmology ◽  
Brane World ◽  
Loop Quantum Cosmology ◽  
Tachyonic Field ◽  
Normal Matter ◽  
Emergent Scenario ◽  
Phantom Scalar ◽  
The Universe ◽  
Kaluza Klein

In this work we have investigated the emergent scenario of the Universe described by loop quantum cosmology model, DGP brane model and Kaluza–Klein cosmology. Scalar field along with barotropic fluid as normal matter is considered as the matter content of the Universe. In loop quantum cosmology it is found that the emergent scenario is realized with the imposition of some conditions on the value of the density of normal matter in case of normal and phantom scalar field. This is a surprising result indeed considering the fact that scalar field is the dominating matter component! In case of tachyonic field, emergent scenario is realized with some constraints on the value of ρ1 for both normal and phantom tachyon. In case of DGP brane-world realization of an emergent scenario is possible almost unconditionally for normal and phantom fields. Plots and table have been generated to testify this fact. In case of tachyonic field emergent scenario is realized with some constraints on [Formula: see text]. In Kaluza–Klein cosmology emergent scenario is possible only for a closed Universe in case of normal and phantom scalar field. For a tachyonic field, realization of emergent Universe is possible for all models (closed, open and flat).

scholarly journals Thermodynamics in Loop Quantum Cosmology

2009 ◽  
Vol 2009 ◽  
pp. 1-9 ◽  
Author(s):  
Li-Fang Li ◽  
Jian-Yang Zhu
Keyword(s):  
Quantum Cosmology ◽  
Apparent Horizon ◽  
Friedmann Equation ◽  
Gravitational Energy ◽  
Effective Density ◽  
Loop Quantum Cosmology ◽  
Thermodynamic Quantities ◽  
Effective Pressure ◽  
The Universe ◽  
Friedmann Robertson Walker

Loop quantum cosmology (LQC) is very powerful to deal with the behavior of early universe. Moreover, the effective loop quantum cosmology gives a successful description of the universe in the semiclassical region. We consider the apparent horizon of the Friedmann-Robertson-Walker universe as a thermodynamical system and investigate the thermodynamics of LQC in the semiclassical region. The effective density and effective pressure in the modified Friedmann equation from LQC not only determine the evolution of the universe in LQC scenario but also are actually found to be the thermodynamic quantities. This result comes from the energy definition in cosmology (the Misner-Sharp gravitational energy) and is consistent with thermodynamic laws. We prove that within the framework of loop quantum cosmology, the elementary equation of equilibrium thermodynamics is still valid.

scholarly journals Anisotropic quantum cosmology with minimally coupled scalar field

2019 ◽  
Vol 34 (34) ◽  
pp. 1950283 ◽  
Author(s):  
Saumya Ghosh ◽  
Sunandan Gangopadhyay ◽  
Prasanta K. Panigrahi
Keyword(s):  
Scalar Field ◽  
Wave Packet ◽  
Quantum Cosmology ◽  
Hamiltonian Formalism ◽  
Big Bang ◽  
Type I ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

In this paper, we perform the Wheeler–DeWitt quantization for Bianchi type I anisotropic cosmological model in the presence of a scalar field minimally coupled to the Einstein–Hilbert gravity theory. We also consider the cosmological (perfect) fluid to construct the matter sector of the model whose dynamics plays the role of time. After obtaining the Wheeler–DeWitt equation from the Hamiltonian formalism, we then define the self-adjointness relations properly. Doing that, we proceed to get a solution for the Wheeler–DeWitt equation and construct a well-behaved wave function for the universe. The wave packet is next constructed from a superposition of the wave functions with different energy eigenvalues together with a suitable weight factor which renders the norm of the wave packet finite. It is then concluded that the Big-Bang singularity can be removed in the context of quantum cosmology.

scholarly journals Effective actions for loop quantum cosmology in fourth-order gravity

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Marcello Miranda ◽  
Daniele Vernieri ◽  
Salvatore Capozziello ◽  
Francisco S. N. Lobo
Keyword(s):  
Quantum Cosmology ◽  
Planck Scale ◽  
Friedmann Equation ◽  
Order Reduction ◽  
Big Bang ◽  
Loop Quantum Cosmology ◽  
Functional Forms ◽  
Alpha Beta ◽  
Theory Of Gravity ◽  
The Big Bang

AbstractLoop quantum cosmology (LQC) is a theory which renders the Big Bang initial singularity into a quantum bounce, by means of short-range repulsive quantum effects at the Planck scale. In this work, we are interested in reproducing the effective Friedmann equation of LQC, by considering a generic f(R, P, Q) theory of gravity, where $$R=g^{\mu \nu }R_{\mu \nu }$$ R = g μ ν R μ ν is the Ricci scalar, $$P=R_{\mu \nu }R^{\mu \nu }$$ P = R μ ν R μ ν , and $$Q=R_{\alpha \beta \mu \nu }R^{\alpha \beta \mu \nu }$$ Q = R α β μ ν R α β μ ν is the Kretschmann scalar. An order reduction technique allows us to work in f(R, P, Q) theories which are perturbatively close to General Relativity, and to deduce a modified Friedmann equation in the reduced theory. Requiring that the modified Friedmann equation mimics the effective Friedmann equation of LQC, we are able to derive several functional forms of f(R, P, Q). We discuss the necessary conditions to obtain viable bouncing cosmologies for the proposed effective actions of f(R, P, Q) theory of gravity.

scholarly journals Thermodynamics in new model of loop quantum cosmology

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
Xiangdong Zhang
Keyword(s):  
Quantum Cosmology ◽  
Apparent Horizon ◽  
Friedmann Equation ◽  
High Energy ◽  
Effective Density ◽  
Loop Quantum Cosmology ◽  
Thermodynamic Quantities ◽  
Effective Pressure ◽  
New Model ◽  
The Universe

AbstractThe thermodynamic properties of loop quantum cosmology (LQC) without considering the Lorentz term were established in Li and Zhu (Adv High Energy Phys 2009:905705, 2009). In this paper, we extend this result to the recent proposed new model of LQC with the Lorentz term. We investigate the thermodynamics of LQC on the apparent horizon of the Friedmann–Lematre–Robertson–Walker universe. The result shows that the effective density and effective pressure in the modified Friedmann equation of LQC not only determines the evolution of the universe but can also serve as the thermodynamic quantities. Moreover, with the help of the Misner–Sharp energy, the first law of thermodynamics of the LQC is still valid as expected. This in turn endows precise physical meaning to the effective matter density $$\rho _{eff}$$ ρ eff and the effective pressure $$P_{eff}$$ P eff .

Coexistence of early-time inflation and late-time acceleration with scalar fields in theory of F(G,T) gravity

2018 ◽  
Vol 27 (08) ◽  
pp. 1850078 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Source Term ◽  
Friedmann Equation ◽  
Early Time ◽  
Scalar Fields ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Late Time Acceleration ◽  
The Universe

In this study, we discuss coexistence of the early-time inflation and the late-time acceleration of the universe in the context of the theory of [Formula: see text] gravity with scalar field which is minimally coupled with the gravity, where [Formula: see text] is the gauss bonnet invariant and [Formula: see text] is the trace of energy–momentum tensor (EMT). We reconstruct the Friedmann equation (FE) and then search for the real value of a particular model [Formula: see text], where [Formula: see text] and [Formula: see text] are real constants. A Gauss–Bonnet system (GBS) for viable cosmologies arising from the matter-source term [Formula: see text] and the scalar field, is obtained. We find that the case [Formula: see text] together with [Formula: see text] in the system gives the late-time cosmic acceleration while the source term [Formula: see text] acts as a quintessence type of dark energy. On the other hand, the general entropy expression of the universe is obtained by making use of the first law of thermodynamics (FLT) method. After theoretically analyzing the inflation in the entropy frame, we find a new condition [Formula: see text] with [Formula: see text] in the system. Then, from the observational analysis of inflation, the spectral index parameter and the scalar-tensor ratio are calculated under the new condition. In brief, we obtain a viable cosmological system arising from some modifications such as the scalar field and the source term, which can unify the early inflation and the late-time cosmic acceleration besides the deceleration regions of the universe.

scholarly journals Preinflationary Dynamics of Power-Law Potential in Loop Quantum Cosmology †

Universe ◽  
2018 ◽  
Vol 4 (8) ◽  
pp. 87 ◽  
Author(s):  
M. Shahalam
Keyword(s):  
Quantum Cosmology ◽  
Initial Conditions ◽  
Big Bang ◽  
Loop Quantum Cosmology ◽  
Inflationary Universe ◽  
Slow Roll ◽  
Wide Range ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

In this article, I mainly discuss the dynamics of the pre-inflationary Universe for the potential V ( ϕ ) ∝ ϕ n with n = 5 / 3 in the context of loop quantum cosmology, in which the big bang singularity is resolved by a non-singular quantum bounce. In the case of the kinetic energy-dominated initial conditions of the scalar field at the bounce, the numerical evolution of the Universe can be split up into three regimes: bouncing, transition, and slow-roll inflation. In the bouncing regime, the numerical evolution of the scale factor does not depend on a wide range of initial values, or on the inflationary potentials. I calculate the number of e-folds in the slow-roll regime, by which observationally identified initial conditions are obtained. Additionally, I display the phase portrait for the model under consideration.

Cosmology of the generalized model of LQG

2020 ◽  
Vol 35 (30) ◽  
pp. 2050247
Author(s):  
Surajit Chattopadhyay ◽  
Martiros Khurshudyan ◽  
K. Myrzakulov ◽  
Antonio Pasqua ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Quantum Cosmology ◽  
Friedmann Equation ◽  
Loop Quantum Cosmology ◽  
De Sitter ◽  
Complicated Case ◽  
Friedmann Equations ◽  
Cosmological Solutions ◽  
Text Model ◽  
Friedmann Robertson Walker

In this paper, we study the main cosmological properties of the classical Friedmann equations in the case of homogeneous and isotropic Friedmann–Robertson–Walker Universe and we also generalized the expression of the Friedmann equation in the case of Loop Quantum Cosmology (LQC). Considering the [Formula: see text]-model, we found the solutions of the equations considered for two particular cases, i.e. [Formula: see text] (i.e. the de Sitter solution) and [Formula: see text]. Moreover, we considered and studied two exact cosmological solutions of the [Formula: see text]-model, in particular the power-law and the exponential ones. Moreover, we also considered a third more complicated case and we derived the solution for an arbitrary function of the time [Formula: see text]. A scalar field description of the model is presented by constructing its self-interacting potential.

scholarly journals Time Direction of Information Propagation and Cosmology

1972 ◽  
Vol 25 (2) ◽  
pp. 207 ◽  
Author(s):  
DT Pegg
Keyword(s):  
Steady State ◽  
Ad Hoc ◽  
Big Bang ◽  
Information Propagation ◽  
The Past ◽  
The Future ◽  
Consistent Solution ◽  
Electrodynamic Theory ◽  
The Universe ◽  
State Universe

In conventional electrodynamic theory, the advanced potential solution of Maxwell's equations is discarded on the ad hoc basis that information can be received from the past only and not from the future. This difficulty is overcome by the Wheeler?Feynman absorber theory, but unfortunately the existence of a completely retarded solution in this theory requires a steady-state universe. In the present paper conventional electrodynamics is used to obtain a condition which, if satisfied, allows information to be received from the past only, and ensures that the retarded potential is the only consistent solution. The condition is that a function Ua of the future structure of the universe is infinite, while the corresponding function Ur of the past structure is finite. Of the currently acceptable cosmological models, only the steady-state, the open big-bang, and the Eddington-Lema�tre models satisfy this condition. In these models there is no need for an ad hoc reason for the preclusion of advanced potentials.

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