scholarly journals NONLINEAR EQUATION OF STATE, COSMIC ACCELERATION AND DECELERATION DURING PHANTOM DOMINANCE

2009 ◽  
Vol 18 (02) ◽  
pp. 329-345 ◽  
Author(s):  
S. K. SRIVASTAVA ◽  
J. DUTTA
Keyword(s):  
Equation Of State ◽  
Nonlinear Equation ◽  
Energy Condition ◽  
Phantom Energy ◽  
Weak Energy Condition ◽  
Cosmic Acceleration ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Acceleration And Deceleration ◽  
The Universe

In this paper, the RS-II model of brane gravity is considered for the phantom universe using a nonlinear equation of state. Phantom fluid is known to violate the weak energy condition. It is found that this characteristic of phantom energy is affected drastically by the negative brane tension λ of the RS-II model. It is interesting to see that up to a certain value of energy density ρ satisfying ρ/λ < 1, the weak energy condition is violated and the universe superaccelerates. But, as ρ increases more, only the strong energy condition is violated and the universe accelerates. When 1 < ρ/λ < 2, even the strong energy condition is not violated and the universe decelerates. Expansion of the universe stops when ρ = 2 λ. This is contrary to earlier results of the phantom universe exhibiting acceleration only.

scholarly journals PHANTOM COSMOLOGY WITH A NONLINEAR BORN–INFELD TYPE SCALAR FIELD

2005 ◽  
Vol 14 (02) ◽  
pp. 355-362 ◽  
Author(s):  
H. Q. LU
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Energy Condition ◽  
State Parameter ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Accelerating Expansion ◽  
Equation Of State Parameter ◽  
The Universe

Recent many physicists suggest that the dark energy in the universe might result from the Born–Infeld (B–I) type scalar field of string theory. The universe of B–I type scalar field with potential can undergo a phase of accelerating expansion. The corresponding equation of state parameter lies in the range of -1<ω<-⅓. The equation of state parameter of B–I type scalar field without potential lies in the range of 0≤ω≤1. We find that weak energy condition and strong energy condition are violated for phantom B–I type scalar field. The equation of state parameter lies in the range of ω<-1.

scholarly journals USING (4+1) SPLIT AND ENERGY CONDITIONS TO STUDY THE INDUCED MATTER IN 5D RICCI-FLAT COSMOLOGY

2007 ◽  
Vol 22 (05) ◽  
pp. 985-994 ◽  
Author(s):  
YONGLI PING ◽  
HONGYA LIU ◽  
LIXIN XU
Keyword(s):  
Energy Condition ◽  
Energy Conditions ◽  
Dominant Energy Condition ◽  
Strong Energy Condition ◽  
Ricci Flat ◽  
Strong Energy ◽  
Expansion Of The Universe ◽  
Frw Models ◽  
Induced Matter ◽  
The Universe

We use (4+1) split to derive the 4D induced energy density ρ and pressure p of the 5D Ricci-flat cosmological solutions which are characterized by having a bounce instead of a bang. The solutions contain two arbitrary functions of time t and, therefore, are mathematically rich in giving various cosmological models. By using four known energy conditions (null, weak, strong, and dominant) to pick out and study physically meaningful solutions, we find that the 4D part of the 5D solutions asymptotically approaches to the standard 4D FRW models and the expansion of the universe is decelerating for normal induced matter for which all the four energy conditions are satisfied. We also find that quintessence might be normal or abnormal, depending on the parameter w of the equation of state. If -1 ≤ w < -1/3, the expansion of the universe is accelerating and the quintessence is abnormal because the strong energy condition is violated while other three are satisfied. For phantom, all the four energy conditions are violated. Before the bounce, all the four energy conditions are violated, implying that the cosmic matter before the bounce could be explained as a phantom that has a large negative pressure and makes the universe bouncing. In the early times after the bounce, the dominant energy condition is violated, while the other three are satisfied, and so the cosmic matter could be explained as a super-luminal acoustic matter.

scholarly journals COMMENTS ON BRANE WORLD COSMOLOGY

2001 ◽  
Vol 16 (18) ◽  
pp. 1157-1169 ◽  
Author(s):  
LUIS ANCHORDOQUI ◽  
KASPER OLSEN
Keyword(s):  
Speed Of Sound ◽  
Energy Condition ◽  
Brane World ◽  
Energy Conditions ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Late Stages ◽  
The Universe ◽  
Nature Of Matter

In this letter we consider some constraints on brane-world cosmologies. In the first part we analyze different behaviors for the expansion of our universe by imposing constraints on the speed of sound. In the second part, we study the nature of matter on the brane world by means of the well-known energy conditions. We find that the strong energy condition must be completely violated at late stages of the universe.

scholarly journals ON BIG RIP SINGULARITIES

2004 ◽  
Vol 19 (33) ◽  
pp. 2479-2484 ◽  
Author(s):  
L. P. CHIMENTO ◽  
RUTH LAZKOZ
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Energy Condition ◽  
Scale Factor ◽  
Late Time ◽  
Strong Energy Condition ◽  
Phantom Field ◽  
Big Rip ◽  
Strong Energy ◽  
Time Singularities

Here we discuss big rip singularities occurring in typical phantom models by violation of the weak energy condition. After that, we compare them with future late-time singularities arising in models where the scale factor ends in a constant value and there is no violation of the strong energy condition. In phantom models the equation of state is well defined along the whole evolution, even at the big rip. However, both the pressure and the energy density of the phantom field diverge. In contrast, in the second kind of model the equation of state is not defined at the big rip because the pressure bursts at a finite value of the energy density.

scholarly journals Necessary conditions for having wormholes in f(R) gravity

2016 ◽  
Vol 31 (37) ◽  
pp. 1650203 ◽  
Author(s):  
S. Habib Mazharimousavi ◽  
M. Halilsoy
Keyword(s):  
Necessary Conditions ◽  
Energy Condition ◽  
Weak Energy Condition ◽  
Polynomial Expansion ◽  
Energy Conditions ◽  
Wormhole Solution ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
External Sources

For a generic f(R) which admits a polynomial expansion, we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such f(R) theories are derived for both zero and nonzero matter sources. For vanishing external sources, we show that the energy conditions are violated. A particular choice of energy–momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters, even the strong energy condition (SEC) is shown to be satisfied.

scholarly journals VIOLATION OF STRONG ENERGY CONDITION IN EFFECTIVE LOOP QUANTUM COSMOLOGY

2007 ◽  
Vol 22 (18) ◽  
pp. 3137-3146 ◽  
Author(s):  
HUA-HUI XIONG ◽  
JIAN-YANG ZHU
Keyword(s):  
Quantum Cosmology ◽  
Small Volume ◽  
Energy Condition ◽  
Matter Field ◽  
Loop Quantum Cosmology ◽  
Quantum Geometry ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Scalar Matter ◽  
The Universe

In loop quantum cosmology nonperturbative modification to a scalar matter field at short scales implies inflation which also means a violation of the strong energy condition. In the framework of effective Hamiltonian we discuss the issue of violation of the strong energy condition in the presence of quantum geometry potential. It is shown that the appearance of quantum geometry potential strengthens the violation of the strong energy condition in small volume regions. In the small volume regions superinflation can easily happen. Furthermore, when the evolution of the universe approaches the bounce scale, this trend of violating the strong energy condition can be greatly amplified.

Repulsive gravitational force and quintessence field in f(T) gravity: How anisotropic compact stars in strong energy condition behave

2021 ◽  
Vol 36 (07) ◽  
pp. 2150044
Author(s):  
Mayukh Bandyopadhyay ◽  
Ritabrata Biswas
Keyword(s):  
Energy Condition ◽  
Cosmic Acceleration ◽  
Compact Stars ◽  
Energy Conditions ◽  
Massachusetts Institute Of Technology ◽  
Strong Energy Condition ◽  
Unknown Parameters ◽  
Strong Energy ◽  
Wide Range ◽  
Quintessence Field

Recently literature is found to be enriched with studies related to anisotropic behaviors of different compact stars in the background of [Formula: see text] gravity in different energy conditions. Quintessence field, as local impacts of cosmic acceleration upon the compact stars, is also very interesting in recent studies. In this paper, the quintessential field effects on the compact stars (mainly on the neutron stars with an wide range of mass distributions), repulsive gravitational effects inside the compact stars due to dark matter distribution in them, charge distribution inside them in strong energy condition, etc. are studied. All required equations of motion using anisotropic property and concept of Massachusetts Institute of Technology bag model are acquired. Black holes surrounded by quintessential matters which satisfy the additive and linearity conditions, with the form of energy tensors were proposed and the corresponding metric was derived by Kiselev.1 The metric, described by Krori and Barua2 with Reissner–Nordström metric3 are compared to find out the different numerical values of unknown parameters. The numerical values are derived and some important parameters like anisotropic stress, adiabatic constant, surface redshift, electric intensity, compactness factor, stability etc. are analyzed deeply to get a clear idea for further study on these types of stars and to understand their nature.

Another Possible Abnormality of Compact Space-Time

1975 ◽  
Vol 18 (5) ◽  
pp. 695-697 ◽  
Author(s):  
K. K. Lee
Keyword(s):  
Compact Space ◽  
Energy Condition ◽  
Space Time ◽  
Energy Conditions ◽  
Strong Energy Condition ◽  
Lorentz Structure ◽  
Strong Energy

AbstractIt is shown that the Lorentz structure of a compact prespace- time M can be so chosen such that M can not satisfy the strong energy condition. Thus, combining both the causal and the strong energy conditions, a stronger case against the compact space-times as proper arenas of physics can be made.

scholarly journals A NEW SINGULARITY THEOREM IN RELATIVISTIC COSMOLOGY

2000 ◽  
Vol 15 (06) ◽  
pp. 391-395 ◽  
Author(s):  
A. K. RAYCHAUDHURI
Keyword(s):  
Ricci Tensor ◽  
Energy Condition ◽  
Space Time ◽  
Relativistic Cosmology ◽  
Raychaudhuri Equation ◽  
Singularity Theorem ◽  
Strong Energy Condition ◽  
Strong Energy

It is shown that if the time-like eigenvector of the Ricci tensor is hypersurface orthogonal so that the space–time allows a foliation into space sections, then the space average of each of the scalars that appears in the Raychaudhuri equation vanishes provided that the strong energy condition holds good. This result is presented in the form of a singularity theorem.

scholarly journals Strong energy condition and the repulsive character of f(R) gravity

2017 ◽  
Vol 49 (4) ◽  
Author(s):  
Crislane S. Santos ◽  
Janilo Santos ◽  
Salvatore Capozziello ◽  
Jailson S. Alcaniz
Keyword(s):  
Energy Condition ◽  
Strong Energy Condition ◽  
Strong Energy
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