scholarly journals A RELATIVISTIC DESCRIPTION OF GENTRY'S NEW REDSHIFT INTERPRETATION

1999 ◽  
Vol 14 (12) ◽  
pp. 779-790
Author(s):  
T. SHIMIZU ◽  
K. WATANABE
Keyword(s):  
Mass Function ◽  
Space Time ◽  
Model Parameters ◽  
De Sitter ◽  
Coordinate Origin ◽  
Walker Metric ◽  
New Interpretation ◽  
Metric Function ◽  
Static Form ◽  
Friedmann Robertson Walker

We obtain a new expression of the Friedmann–Robertson–Walker metric, which is an analogue of a static chart of the de Sitter space–time. The reduced metric contains two functions, M(T, R) and Ψ(T, R), which are interpreted as, respectively, the mass function and the gravitational potential. We find that, near the coordinate origin, the reduced metric can be approximated in a static form and that the approximated metric function, Ψ(R) satisfies the Poisson equation. Moreover, when the model parameters of the Friedmann–Robertson–Walker metric are suitably chosen, the approximated metric coincides with exact solutions of the Einstein equation with the perfect fluid matter. We then solve the radial geodesics on the approximated space–time to obtain the distance-redshift relation of geodesic sources observed by the comoving observer at the origin. We find that the redshift is expressed in terms of a peculiar velocity of the source and the metric function, Ψ(R), evaluated at the source position, and one may think that this is a new interpretation of Gentry's new redshift interpretation.

scholarly journals STANDARD COSMOLOGY FROM THE BRANE COSMOLOGY WITH A LOCALIZED MATTER

2002 ◽  
Vol 17 (29) ◽  
pp. 1915-1922 ◽  
Author(s):  
Y. S. MYUNG
Keyword(s):  
Space Time ◽  
Negative Sign ◽  
Massless Scalar ◽  
Charged Dust ◽  
De Sitter ◽  
Brane Cosmology ◽  
Stiff Matter ◽  
Standard Cosmology ◽  
Friedmann Robertson Walker

We discuss the brane cosmology in the 5D anti de Sitter Reissner–Nordstrom ( AdSRN 5) space–time. A brane with tension σ is defined as the edge of an AdSRN 5 space with mass M and charge Q. In this case we get the CFT-radiation term (ρ CFT ) from M and the charged dust [Formula: see text] from Q2 in the Friedmann-like equation. However, this equation is not justified because it contains [Formula: see text]-term with the negative sign. This is unconventional in view of the standard cosmology. In order to resolve this problem, we introduce a localized dust matter which satisfies Pdm = 0. If [Formula: see text], the unwanted [Formula: see text] is cancelled against [Formula: see text] and thus one recovers a standard Friedmann–Robertson–Walker universe with CFT-radiation and dust matter. For the stiff matter consideration, we can set ρcsti ~ Q2 with the negative sign. Here we introduce a massless scalar which plays the role of a stiff matter with Psca = ρsca to cancel -ρcsti. In this case, however, we find a mixed version of the standard and brane cosmologies.

Expansion and collapse of spherical source with cosmological constant

2019 ◽  
Vol 34 (05) ◽  
pp. 1950042
Author(s):  
G. Abbas ◽  
Shahid Qaisar ◽  
Hamood Ur Rehman ◽  
M. Younas
Keyword(s):  
Cosmological Constant ◽  
Mass Function ◽  
Parametric Form ◽  
De Sitter ◽  
Field Equations ◽  
Spherical Source ◽  
Expansion Scalar ◽  
Radial Heat ◽  
Metric Functions ◽  
Metric Function

In this research paper, we address the issues of expansion and gravitational collapse of anisotropic spherical source in the presence of cosmological constant. For this purpose, we have solved the Einstein field equations with gravitating source and cosmological constant. The absence of radial heat flux in the gravitating source provide the parametric form of two-metric functions in terms of a single-metric function. The expansion scalar and the mass function of the gravitating source is evaluated for the given metric. The trapping condition is applied to mass function which implies the existence of horizons, like the horizons of Schwarzschild de-Sitter black holes. The trapping condition provides the parametric form of the unknown metric function. The value of expansion scalar has been analyzed in detail to see its positivity and negativity, which correspond to expansion and collapse, respectively. So, the values of parameter [Formula: see text] for which expansion scalar is positive have been used to analyze the other physical variables including density, pressures and anisotropy. The same quantities have been evaluated for the values of [Formula: see text] that result in the negative values of expansion scalar leading to collapse. The effects of positive cosmological constant have been noted in both expansion and collapse solutions. Due to the presence of cosmological constant after collapse, there would occur inner and outer horizons or a unique horizon depending on the value of mass of the gravitating source.

scholarly journals Inflationary cosmology in unimodular F(T) gravity

2017 ◽  
Vol 32 (21) ◽  
pp. 1750114 ◽  
Author(s):  
Kazuharu Bamba ◽  
Sergei D. Odintsov ◽  
Emmanuel N. Saridakis
Keyword(s):  
Spectral Index ◽  
Teleparallel Gravity ◽  
Specific Model ◽  
Inflationary Cosmology ◽  
Model Parameters ◽  
De Sitter ◽  
Reconstruction Procedure ◽  
Additional Advantage ◽  
Slow Roll ◽  
Good Agreement

We investigate the inflationary realization in the context of unimodular F(T) gravity, which is based on the F(T) modification of teleparallel gravity, in which one imposes the unimodular condition through the use of Lagrange multipliers. We develop the general reconstruction procedure of the F(T) form that can give rise to a given scale-factor evolution, and then we apply it in the inflationary regime. We extract the Hubble slow-roll parameters that allow us to calculate various inflation-related observables, such as the scalar spectral index and its running, the tensor-to-scalar ratio, and the tensor spectral index. Then, we examine the particular cases of de Sitter and power-law inflation, of Starobinsky inflation, as well as inflation in a specific model of unimodular F(T) gravity. As we show, in all cases the predictions of our scenarios are in a very good agreement with Planck observational data. Finally, inflation in unimodular F(T) gravity has the additional advantage that it always allows for a graceful exit for specific regions of the model parameters.

Discreteness of Space and Its Consequences

2021 ◽  
pp. 132-141
Author(s):  
Аnatoly М. Shutyi ◽  
Keyword(s):  
Spatial Configuration ◽  
Relativistic Effects ◽  
Space Time ◽  
Maximum Speed ◽  
Speed Of Light ◽  
Quantum Uncertainty ◽  
Proposed Model ◽  
Spatial Configurations ◽  
New Interpretation ◽  
Component Particle

Based on the general principle of the unity of the nature of interacting entities and the principle of the relativity of motion, as well as following the requirement of an indissoluble and conditioning connection of space and time, the model of a discrete space-time consisting of identical interacting particles is proposed as the most acceptable one. We consider the consequences of the discreteness of space, such as: the occurrence of time quanta, the limiting speed of signal propa­gation, and the constancy of this speed, regardless of the motion of the reference frame. Regularly performed acts of particles of space-time (PST) interaction en­sure the connectivity of space, set the quantum of time and the maximum speed – the speed of light. In the process of PST communication, their mixing occurs, which ensures the relativity of inertial motion, and can also underlie quantum uncertainty. In this case, elementary particles are spatial configurations of an excited “lattice” of PST, and particles with mass must contain loop struc­tures in their configuration. A new interpretation of quantum mechanics is pro­posed, according to which the wave function determines the probability of de­struction of a spatial configuration (representing a quantum object) in its corresponding region, which leads to the contraction of the entire structure to a given, detectable component. Particle entanglement is explained by the appear­ance of additional links between the PST – the appearance of a local coordinate along which the distance between entangled objects does not increase. It is shown that the movement of a body should lead to an asymmetry of the tension of the bonds between the PST – to the asymmetry of its effective gravity, the es­tablishment of which is one of the possibilities for experimental verification of the proposed model. It is shown that the constancy of the speed of light in a vac­uum and the appearance of relativistic effects are based on ensuring the connec­tivity of space-time, i.e. striving to prevent its rupture.

Noncommutative scalar field in de Sitter space–time and pair creation process

2021 ◽  
Vol 36 (02) ◽  
pp. 2150011
Author(s):  
Nabil Mehdaoui ◽  
Lamine Khodja ◽  
Salah Haouat
Keyword(s):  
Scalar Field ◽  
Chemical Potential ◽  
De Sitter Space ◽  
Space Time ◽  
Pair Creation ◽  
De Sitter ◽  
Creation Process ◽  
Scalar Particles ◽  
Constant Electromagnetic Field

In this work, we address the process of pair creation of scalar particles in [Formula: see text] de Sitter space–time in presence of a constant electromagnetic field by applying the noncommutativity on the scalar field up to first-order in [Formula: see text]. We calculate the density of particles created in the vacuum by the mean of the Bogoliubov transformations. In contrast to a previous result, we show that noncommutativity contributes to the pair creation process. We find that the noncommutativity plays the same role of chemical potential and gives an important interest for studies at high energies.

scholarly journals De Sitter and power-law solutions in non-local Gauss–Bonnet gravity

2018 ◽  
Vol 15 (11) ◽  
pp. 1850188 ◽  
Author(s):  
E. Elizalde ◽  
S. D. Odintsov ◽  
E. O. Pozdeeva ◽  
S. Yu. Vernov
Keyword(s):  
Power Law ◽  
Sufficient Conditions ◽  
Model Parameters ◽  
Local Form ◽  
De Sitter ◽  
Dynamical Equations ◽  
Non Local ◽  
Necessary And Sufficient ◽  
The Universe ◽  
Universe Evolution

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d’Alembertian, is investigated. Casting the dynamical equations into local form, the fixed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows to describe the matter-dominated phase of the Universe evolution.

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