scholarly journals Thermodynamics of flat FLRW universe in Rastall theory

2016 ◽  
Vol 757 ◽  
pp. 187-191 ◽  
Author(s):  
H. Moradpour
Keyword(s):  
Flrw Universe

scholarly journals Time-covariant Schrödinger equation and invariant decay probability: the $$\Lambda $$-Kantowski–Sachs universe

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Theodoros Pailas ◽  
Nikolaos Dimakis ◽  
Petros A. Terzis ◽  
Theodosios Christodoulakis
Keyword(s):  
Schrödinger Equation ◽  
Wave Packet ◽  
Time Dependence ◽  
Schrodinger Equation ◽  
Canonical Quantization ◽  
Dynamical Equations ◽  
Quadratic Constraint ◽  
Decay Probability ◽  
Flrw Universe ◽  
Arbitrary Time Dependence

AbstractThe system under study is the $$\Lambda $$ Λ -Kantowski–Sachs universe. Its canonical quantization is provided based on a recently developed method: the singular minisuperspace Lagrangian describing the system, is reduced to a regular (by inserting into the dynamical equations the lapse dictated by the quadratic constraint) possessing an explicit (though arbitrary) time dependence; thus a time-covariant Schrödinger equation arises. Additionally, an invariant (under transformations $$t=f({\tilde{t}})$$ t = f ( t ~ ) ) decay probability is defined and thus “observers” which correspond to different gauge choices obtain, by default, the same results. The time of decay for a Gaussian wave packet localized around the point $$a=0$$ a = 0 (where a the radial scale factor) is calculated to be of the order $$\sim 10^{-42}{-}10^{-41}~\text {s}$$ ∼ 10 - 42 - 10 - 41 s . The acquired value is near the end of the Planck era (when comparing to a FLRW universe), during which the quantum effects are most prominent. Some of the results are compared to those obtained by following the well known canonical quantization of cosmological systems, i.e. the solutions of the Wheeler–DeWitt equation.

scholarly journals PRE-INFLATION IN THE PRESENCE OF CONFORMAL COUPLING

2004 ◽  
Vol 19 (11) ◽  
pp. 807-816
Author(s):  
APOSTOLOS KUIROUKIDIS ◽  
DEMETRIOS B. PAPADOPOULOS
Keyword(s):  
Scalar Field ◽  
Exact Solutions ◽  
Hubble Parameter ◽  
Field Potential ◽  
Critical Value ◽  
Big Bang ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Conformal Parameter ◽  
Flrw Universe

We consider a massless scalar field, conformally coupled to the Ricci scalar curvature, in the pre-inflation era of a closed FLRW Universe. The scalar field potential can be of the form of the Coleman–Weinberg one-loop potential, which is flat at the origin and drives the inflationary evolution. For positive values of the conformal parameter ξ, less than the critical value ξ c =(1/6), the model admits exact solutions with nonzero minimum scale factor and zero initial Hubble parameter. Thus these solutions can be matched smoothly to the so-called Pre-Big-Bang models. At the end of this pre-inflation era one can match inflationary solutions by specifying the form of the potential and the whole solution is of the class C(1).

scholarly journals Cosmological hyperfluids, torsion and non-metricity

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
Damianos Iosifidis
Keyword(s):  
Conservation Laws ◽  
Previous Model ◽  
Covariant Form ◽  
Future Directions ◽  
Affine Spaces ◽  
Cosmological Principle ◽  
Friedmann Equations ◽  
Flrw Universe ◽  
Novel Model

AbstractWe develop a novel model for cosmological hyperfluids, that is fluids with intrinsic hypermomentum that induce spacetime torsion and non-metricity. Imposing the cosmological principle to metric-affine spaces, we present the most general covariant form of the hypermomentum tensor in an FLRW Universe along with its conservation laws and therefore construct a novel hyperfluid model for cosmological purposes. Extending the previous model of the unconstrained hyperfluid in a cosmological setting we establish the conservation laws for energy–momentum and hypermomentum and therefore provide the complete cosmological setup to study non-Riemannian effects in Cosmology. With the help of this we find the forms of torsion and non-metricity that were earlier reported in the literature and also obtain the most general form of the Friedmann equations with torsion and non-metricity. We also discuss some applications of our model, make contact with the known results in the literature and point to future directions.

scholarly journals A dark energy quintessence model of the universe

2019 ◽  
Vol 35 (04) ◽  
pp. 2050002
Author(s):  
G. K. Goswami ◽  
Anirudh Pradhan ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Time Dependent ◽  
Observational Constraints ◽  
History Of ◽  
Flrw Universe ◽  
The Universe ◽  
Quintessence Model

In this paper, we have presented a model of the Friedmann–Lemaitre–Robertson–Walker (FLRW) universe filled with matter and dark energy (DE) fluids by assuming an ansatz that deceleration parameter (DP) is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating–accelerating transition phase of the universe. This is a quintessence model [Formula: see text]. The quintessence phase remains for the period [Formula: see text]. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated.

scholarly journals Quintom cosmological model and some possible solutions using Lie and Noether symmetries

2016 ◽  
Vol 25 (14) ◽  
pp. 1650110 ◽  
Author(s):  
Sourav Dutta ◽  
Muthusamy Lakshmanan ◽  
Subenoy Chakraborty
Keyword(s):  
Lie Algebra ◽  
Physical System ◽  
Three Dimensional ◽  
Noether Symmetry ◽  
Conserved Quantities ◽  
Considerable Simplification ◽  
Present Context ◽  
Augmented Space ◽  
Constants Of Motion ◽  
Flrw Universe

The present work deals with a quintom model of dark energy in the framework of a spatially flat isotropic and homogeneous Friedmann–Lemaitre–Robertson–Walker (FLRW) universe. At first, Lie point symmetry is imposed to the system and the unknown coupled potential of the model is determined. Then Noether symmetry, which is also a point like symmetry of the Lagrangian, is imposed on the physical system and the potential takes a general form. It is shown that the Lie algebra of Noether symmetry is a sub-algebra of the corresponding Lie algebra of the Lie symmetry. Finally, a point transformation in the three-dimensional augmented space is performed suitably so that one of the variables become cyclic and as a result there is considerable simplification to the physical system. Hence, conserved quantities (i.e. constants of motion) are expressed in a compact form and cosmological solutions are evaluated and analyzed in the present context.

scholarly journals Proposal for the proper gravitational energy–momentum tensor

2016 ◽  
Vol 31 (26) ◽  
pp. 1650151 ◽  
Author(s):  
Katsutaro Shimizu
Keyword(s):  
Black Hole ◽  
Energy Momentum Tensor ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Gravitational Energy ◽  
Coordinate Transformations ◽  
Black Hole Mass ◽  
Schwarzschild Black Hole ◽  
Flrw Universe ◽  
Energy Momentum Conservation

We propose a gravitational energy–momentum (GEMT) tensor of the general relativity obtained using Noether’s theorem. It transforms as a tensor under general coordinate transformations. One of the two indices of the GEMT labels a local Lorentz frame that satisfies the energy–momentum conservation law. The energies for a gravitational wave, a Schwarzschild black hole and a Friedmann–Lemaitre–Robertson–Walker (FLRW) universe are calculated as examples. The gravitational energy of the Schwarzschild black hole exists only outside the horizon, its value being the negative of the black hole mass.

scholarly journals Thermodynamics of f(R) Gravity with Disformal Transformation

Entropy ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 172 ◽  
Author(s):  
Chao-Qiang Geng ◽  
Wei-Cheng Hsu ◽  
Jhih-Rong Lu ◽  
Ling-Wei Luo
Keyword(s):  
Hubble Parameter ◽  
Equations Of State ◽  
Kinetic Term ◽  
Laws Of Thermodynamics ◽  
Flrw Universe

We study thermodynamics in f ( R ) gravity with the disformal transformation. The transformation applied to the matter Lagrangian has the form of γ μ ν = A ( ϕ , X ) g μ ν + B ( ϕ , X ) ∂ μ ϕ ∂ ν ϕ with the assumption of the Minkowski matter metric γ μ ν = η μ ν , where ϕ is the disformal scalar and X is the corresponding kinetic term of ϕ . We verify the generalized first and second laws of thermodynamics in this disformal type of f ( R ) gravity in the Friedmann-Lemaître-Robertson-Walker (FLRW) universe. In addition, we show that the Hubble parameter contains the disformally induced terms, which define the effectively varying equations of state for matter.

scholarly journals Clock Time in Quantum Cosmology

Universe ◽  
2019 ◽  
Vol 5 (2) ◽  
pp. 66
Author(s):  
Marcello Rotondo ◽  
Yasusada Nambu
Keyword(s):  
Harmonic Oscillator ◽  
Quantum Cosmology ◽  
Schrodinger Equation ◽  
Semiclassical Limit ◽  
Cosmic Time ◽  
Wave Functions ◽  
Degree Of Freedom ◽  
Clock Time ◽  
Quantum Harmonic Oscillator ◽  
Flrw Universe

We consider the conditioning of the timeless solution to the Wheeler–DeWitt equation by a predefined matter clock state in the simple scenario of an FLRW universe. The resulting evolution of the geometrodynamical degree of freedom with respect to clock time is characterized by the “Berry connection” of the reduced geometrodynamical space, which relies on the coupling of the clock with the geometry. When the connection vanishes, the standard Schrödinger equation is obtained for the geometry with respect to clock time. When one considers environment-induced decoherence in the semiclassical limit, this condition is satisfied, and clock time coincides with cosmic time. Explicit results for the conditioned wave functions for minimal clocks made up of two quantum harmonic oscillator eigenstates are shown.

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