scholarly journals Bounce and Stability in the Early Cosmology with Anomaly-Induced Corrections

Symmetry ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 50
Author(s):  
Wagno Cesar e Silva ◽  
Ilya L. Shapiro
Keyword(s):  
Background Radiation ◽  
Cosmological Solution ◽  
Stable Phase ◽  
Small Perturbations ◽  
Critical Part ◽  
Contraction Phase ◽  
Exponential Expansion ◽  
Expansion Of The Universe ◽  
The Stability ◽  
The Universe

An extremely fast exponential expansion of the Universe is typical for the stable version of the inflationary model, based on the anomaly-induced action of gravity. The total amount of exponential e-folds could be very large, before the transition to the unstable version and the beginning of the Starobinsky inflation. Thus, the stable exponential expansion can be seen as a pre-inflationary semiclassical cosmological solution. We explore whether this stable phase could follow after the bounce, subsequent to the contraction of the Universe. Extending the previous consideration of the bounce, we explore both stable expansion and the bounce solutions in the models with non-zero cosmological constant and the presence of background radiation. The critical part of the analysis concerns stability for small perturbations of the Hubble parameter. It is shown that the stability is possible for the variations in the bounce region, but not in the sufficiently distant past in the contraction phase.

scholarly journals Dynamical Stability of Bulk Viscous Isotropic and Homogeneous Universe

Universe ◽  
2019 ◽  
Vol 5 (8) ◽  
pp. 185
Author(s):  
Muhammad Sharif ◽  
Qanitah Ama-Tul-Mughani
Keyword(s):  
Accelerated Expansion ◽  
Stationary Points ◽  
Late Time ◽  
Energy Models ◽  
Bulk Viscous ◽  
Expansion Of The Universe ◽  
Homogeneous Universe ◽  
The Stability ◽  
The Universe ◽  
Autonomous Set

In this paper, we study the phase space portrait of homogeneous and isotropic universe by taking different coupling functions between dark energy models and bulk viscous dark matter. The dimensionless quantities are introduced to establish an autonomous set of equations. To analyze the stability of the cosmos, we evaluate critical points and respective eigenvalues for different dynamical quantities. For bulk viscous matter and radiation in tachyon coupled field, these points show stable evolution when γ ≫ δ but accelerated expansion of the universe for δ > 1 9 . The stability of the universe increases for some stationary points which may correspond to the late-time expansion for the coupled phantom field.

scholarly journals Small Scale Fluctuations in the Microwave Background Radiation Associated with the Formation of Galaxies

1977 ◽  
Vol 74 ◽  
pp. 327-334
Author(s):  
R. A. Sunyaev
Keyword(s):  
Spatial Distribution ◽  
Background Radiation ◽  
Gravitational Instability ◽  
Thomson Scattering ◽  
Small Scale ◽  
Clusters Of Galaxies ◽  
Microwave Background ◽  
Microwave Background Radiation ◽  
Expansion Of The Universe ◽  
The Universe

According to current ideas, massive extragalactic systems such as galaxies and clusters of galaxies formed as a result of the growth of small fluctuations in density and velocity which were present in the early stages of expansion of the Universe under the influence of gravitational instability. According to the hot model of the Universe at the epoch corresponding to a redshift z ≈ 1500, recombination of primaeval hydrogen took place and as a result the optical depth of the Universe to Thomson scattering decreased abruptly from about 1000 to 1 - the Universe became transparent. Therefore the observed angular distribution of the microwave background radiation (MWBR) contains information about inhomogeneities in its spatial distribution at a redshift z ∼ 1000. Silk (1968) was the first to note that this “photograph” of the Universe at the epoch of recombination must be enscribed with fluctuations associated with perturbations in the space density and velocity of motion of matter which will later lead to the formation of galaxies and clusters of galaxies.

Thermodynamics of generalized cosmic Chaplygin gas model

2016 ◽  
Vol 31 (10) ◽  
pp. 1650061 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Sarwar
Keyword(s):  
Isothermal Condition ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Stability Conditions ◽  
Expansion Of The Universe ◽  
The Stability ◽  
Generalized Cosmic Chaplygin Gas ◽  
The Universe ◽  
Thermal Stability Of

In this paper, we study thermal stability of an exotic fluid known as generalized cosmic Chaplygin gas (GCCG). We evaluate different physical parameters and examine how this fluid describes accelerated expansion of the universe. The stability conditions are formulated from thermodynamics which indicate that the respective fluid is stable adiabatically but it cannot be checked under isothermal condition.

OBSERVATIONAL COSMOLOGY 2004: WHAT THE DATA SAY ABOUT DARK ENERGY AND THE CONTENTS OF THE UNIVERSE

2005 ◽  
Vol 20 (14) ◽  
pp. 2931-2942
Author(s):  
JOSEPH FOWLER
Keyword(s):  
Dark Energy ◽  
Background Radiation ◽  
Current Data ◽  
Observational Cosmology ◽  
Microwave Background ◽  
Hubble Expansion ◽  
Microwave Background Radiation ◽  
Expansion Of The Universe ◽  
Cosmological Data ◽  
The Universe

The latest cosmological data point to a model of the universe that is self-consistent but deeply weird. It seems that most matter in our universe is non-baryonic and hidden from direct view. Meanwhile, a repulsive "dark energy" causes the expansion of the universe to proceed at an accelerating rate. Sources of current data include studies of the distribution of matter in the universe, the anisotropies of the cosmic microwave background radiation, and the Hubble expansion law as probed by distant supernovae. In the near future, we can hope that measurements like these will begin to illuminate the nature of dark energy, starting with the question of whether it behaves like a cosmological constant or shows a more complicated evolution.

scholarly journals Dynamical analysis of autonomous system in entropic cosmology

2016 ◽  
Vol 94 (5) ◽  
pp. 458-465
Author(s):  
Yu Li
Keyword(s):  
Fixed Points ◽  
Autonomous System ◽  
Constant Term ◽  
Accelerated Expansion ◽  
Dynamical Analysis ◽  
Stability Properties ◽  
Expansion Of The Universe ◽  
Dynamical Properties ◽  
The Stability ◽  
The Universe

The entropic cosmology model is an alternative method to explain the accelerated expansion of the universe. In this paper, we discuss the dynamical system in two types of entropic cosmology model: Λ(t) type and bulk viscous type. We found that the stability properties of fixed points are affected by the H2 term, while the H term and constant term have no influence on stability properties of fixed points. We also found that the dynamical properties of the C-version model are the same as the H-version model.

scholarly journals Exact scalar–tensor cosmological models

2017 ◽  
Vol 26 (07) ◽  
pp. 1750073 ◽  
Author(s):  
J. A. Belinchón ◽  
T. Harko ◽  
M. K. Mak
Keyword(s):  
Scalar Field ◽  
Cosmological Solution ◽  
Gravitational Theory ◽  
Field Equations ◽  
Group Approach ◽  
Gravitational Field Equations ◽  
Gravitational Theories ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Scalar–tensor gravitational theories are important extensions of standard general relativity, which can explain both the initial inflationary evolution, as well as the late accelerating expansion of the universe. In the present paper, we investigate the cosmological solution of a scalar–tensor gravitational theory, in which the scalar field [Formula: see text] couples to the geometry via an arbitrary function [Formula: see text]. The kinetic energy of the scalar field as well as its self-interaction potential [Formula: see text] are also included in the gravitational action. By using a standard mathematical procedure, the Lie group approach, and Noether symmetry techniques, we obtain several exact solutions of the gravitational field equations describing the time evolutions of a flat Friedman–Robertson–Walker universe in the framework of the scalar–tensor gravity. The obtained solutions can describe both accelerating and decelerating phases during the cosmological expansion of the universe.

scholarly journals The Expansion of the Universe

2020 ◽  
Vol 8 (07) ◽  
pp. 25-31
Author(s):  
Dr. Andreas Gimsa
Keyword(s):  
Background Radiation ◽  
Expanding Universe ◽  
Stellar Radiation ◽  
Expansion Of The Universe ◽  
Accelerated Growth ◽  
The Universe ◽  
Physical Quantities

The expansion of the universe is explained, calculated and graphically displayed. The 3K background radiation is examined and interpreted as reflected and distributed stellar radiation. The role of entropy in cosmology is discussed. In our expanding universe it must remain constant. Physical quantities previously assumed to be constant are worked out to be variable. It is explained why the measured redshift is not due to an accelerated growth of the universe.

scholarly journals The expansion of the Universe may be an illusion created by Compton scattering of free electrons

2021 ◽  
Author(s):  
GuanFeng Cheng
Keyword(s):  
Compton Scattering ◽  
New Physics ◽  
Precision Measurements ◽  
Free Electrons ◽  
Expansion Factor ◽  
Distant Galaxy ◽  
Cosmological Redshift ◽  
Exponential Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Abstract The high-precision measurements of the Hubble parameter make the theory of cosmic expansion more and more confusing, which bolster the idea that new physics may be needed to explain the mismatch. The cosmological redshift may not only be related to distance but also to other factors. The expansion of the Universe may be just an illusion. The Compton effect of free electrons and low energy photons has been observed in the laboratory. This article proposes a theory: Free electron Compton scattering (FEC) produce the illusion of the Universe exponential expansion: FEC causes photons to redshift (FEC redshift), and the photon beam expands along the propagation direction, that is, the redshift factor is (1 + z); the beam length stretch factor (time dilation of the supernova curve) is (1 + z); the expansion factor of the beam volume is (1 + z)3, and FEC will not be blurred Distant galaxy. The reason for rejecting the “tired light” does not hold in FEC.

scholarly journals R2 Gravity and the Structure of the Universe

1983 ◽  
Vol 104 ◽  
pp. 483-484
Author(s):  
Kenneth Brecher
Keyword(s):  
Background Radiation ◽  
Big Bang ◽  
Microwave Background ◽  
The Standard Model ◽  
Microwave Background Radiation ◽  
Expansion Of The Universe ◽  
High Degree ◽  
Cosmological Constants ◽  
The Universe ◽  
Fundamental Physical

The “standard” hot big bang model accounts for the expansion of the Universe, the existence of the microwave background radiation, and the mass fraction of the light elements up to 4He. It does not account for the high degree of isotropy and homogeneity of the Universe in the large, nor of the existence of structure (galaxies, clusters) on smaller scales. Other problems, such as the lepton to baryon ratio, the preponderance of matter over antimatter, and the “coincidences” of dimensionless ratios of several fundamental physical and cosmological “constants” also lie outside of the “standard” model at present.

BLACK HOLE SINGULARITIES, CRITICAL PHENOMENA, THE RUNAWAY UNIVERSE AND HYPERSPACE TRAVEL

2003 ◽  
Vol 12 (09) ◽  
pp. 1675-1680
Author(s):  
LIOR M. BURKO
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Energy ◽  
Radiation Field ◽  
Background Radiation ◽  
Cosmic Background Radiation ◽  
Radiation Fields ◽  
Cosmic Background ◽  
Expansion Of The Universe ◽  
The Universe

Black holes are always irradiated by the cosmic background radiation. This captured radiation field determines the physical and geometrical nature of the singularity inside the black hole. We find that non-compact radiation fields (similar to the cosmic background radiation) affect dramatically the singularity, and may determine the fate of a falling astronaut. In particular, the dark energy which accelerates the expansion of the universe determines whether the "tunnel" inside the black hole is blocked, or whether the possibility of using the black hole as a portal for hyperspace travel cannot be ruled out as yet.

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