scholarly journals Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

Built-in inflation in f(G) gravity

2016 ◽  
Vol 25 (01) ◽  
pp. 1650011 ◽  
Author(s):  
M. Sharif ◽  
H. Ismat Fatima
Keyword(s):  
Energy Density ◽  
Late Time ◽  
Universe Model ◽  
Frw Universe ◽  
Eos Parameter ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Bonnet Term

In this paper, we study the role of Gauss–Bonnet term for the early and late time accelerating phases of the universe with the help of two viable [Formula: see text] models in the background of flat FRW universe model. These models show inflationary behavior as well as the present accelerating expansion of the universe. The contribution of Gauss–Bonnet term in pressure and energy density is used to calculate equation of state (EoS) parameter for the modified fluid which behaves like cosmological constant with [Formula: see text]. We discuss early inflation and late accelerating expansion of the universe through scale factor evaluated from equation of continuity numerically.

ENTROPY CORRECTED HOLOGRAPHIC DARK ENERGY f(T) GRAVITY MODEL

2014 ◽  
Vol 29 (02) ◽  
pp. 1450015 ◽  
Author(s):  
M. SHARIF ◽  
SHAMAILA RANI
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Phase Plane ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Statefinder Parameters ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Evolution Trajectory

This paper is devoted to study the power-law entropy corrected holographic dark energy (ECHDE) model in the framework of f(T) gravity. We assume infrared (IR) cutoff in terms of Granda–Oliveros (GO) length and discuss the constructed f(T) model in interacting as well as in non-interacting scenarios. We explore some cosmological parameters like equation of state (EoS), deceleration, statefinder parameters as well as ωT–ωT′ analysis. The EoS and deceleration parameters indicate phantom behavior of the accelerated expansion of the universe. It is mentioned here that statefinder trajectories represent consistent results with ΛCDM limit, while evolution trajectory of ωT–ωT′ phase plane does not approach to ΛCDM limit for both interacting and non-interacting cases.

Rotation as a Source of Accelerating Expansion of the Universe

2021 ◽  
Author(s):  
Andrzej Szummer
Keyword(s):  
Gravitational Force ◽  
Cosmological Parameters ◽  
Classical Mechanics ◽  
Astronomical Observations ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Difference ◽  
Changes Over Time ◽  
The Universe ◽  
Over Time

Abstract Assuming a hypothesis, that the universe is rotating from the very beginning – as soon as it appeared- creates new possibilities to explain accelerating expansion of the universe. A spinning universe is under the action of two enormous forces: gravitational force and centrifugal force. The difference between the two forces has been shown to give the resultant force that causes the expansion of the universe to accelerate. Applying classical mechanics as a method, I calculated the magnitude of this acceleration, the time when it appeared and how it changes over time. By applying only recognized cosmological parameters, interesting results were obtained that can be checked with astronomical observations. The presence of acceleration of expansion causes the rate of expansion of the universe to continue to increase, which is consistent with astronomical observations. However, the speed of this increase in the rate of expansion becomes slower over time.

scholarly journals THE EVOLUTION OF THE UNIVERSE WITH THE B–I TYPE PHANTOM SCALAR FIELD

2006 ◽  
Vol 15 (02) ◽  
pp. 199-214 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
Z. G. HUANG ◽  
K. F. ZHANG
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Phase Plane Analysis ◽  
Density Parameter ◽  
Late Time ◽  
Plane Analysis ◽  
Accelerating Expansion ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe

We consider the phantom cosmology with a Lagrangian [Formula: see text] originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(Xc) at the critical point (Xc, 0) should be maximum and greater than zero. We study a specific potential with the form of [Formula: see text] via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ωϕ≃10-12 at the equipartition epoch), and also avoid the future collapse of the universe.

Gödel-type universe in f(R,G) gravity

2019 ◽  
Vol 16 (12) ◽  
pp. 1950188 ◽  
Author(s):  
M. Farasat Shamir ◽  
Saeeda Zia
Keyword(s):  
Equation Of State ◽  
Graphical Analysis ◽  
Gravity Models ◽  
Energy Conditions ◽  
Radial Coordinate ◽  
Model Parameters ◽  
Cylindrical Coordinates ◽  
Polytropic Equation ◽  
Expansion Of The Universe ◽  
The Universe

In the current study, we discuss Gödel-type universe in [Formula: see text] gravity. Analysis has been done by considering anisotropic and perfect fluid distributions. Energy conditions for two proposed [Formula: see text] gravity models have been studied for suitable values of model parameters. Furthermore, Tolman–Oppenheimer–Volkoff equation has been developed with cylindrical coordinates in [Formula: see text] gravity. The graphical analysis for both these models suggests that Tolman–Oppenheimer–Volkoff equation is obeyed in a specific interval for the radial coordinate [Formula: see text]. A polytropic equation of state has been discussed for two [Formula: see text] gravity models. By analyzing the energy conditions, it is concluded that Gödel-type universe with both [Formula: see text] gravity models supports the expansion of the universe for certain range of radial coordinates.

scholarly journals Accelerating universe in modified teleparallel gravity theory

2019 ◽  
Vol 15 (S356) ◽  
pp. 397-399
Author(s):  
Shambel Sahlu ◽  
Joseph Ntahompagaze ◽  
Amare Abebe ◽  
David F. Mota
Keyword(s):  
State Parameter ◽  
Teleparallel Gravity ◽  
Gravity Theory ◽  
Gravity Models ◽  
Accelerating Universe ◽  
Late Time ◽  
Numerical Result ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

AbstractThis paper studies the cosmology of accelerating expansion of the universe in modified teleparallel gravity theory. We discuss the cosmology of f(T, B) gravity theory and its implication to the new general form of the equation of state parameter wTB for explaining the late-time accelerating expansion of the universe without the need for the cosmological constant scenario. We examine the numerical value of wTB in different paradigmatic f(T, B) gravity models. In those models, the numerical result of wTB is favored with observations in the presence of the torsion scalar T associated with a boundary term B and shows the accelerating expansion of the universe.

scholarly journals FLRW Cosmological Models with Dynamic Cosmological Term in Modified Gravity

Universe ◽  
2021 ◽  
Vol 7 (9) ◽  
pp. 319
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Bhupendra Kumar Shukla
Keyword(s):  
Cosmological Model ◽  
Cold Dark Matter ◽  
Background Radiation ◽  
Cosmological Term ◽  
Energy Conditions ◽  
Physical Parameters ◽  
Late Time ◽  
Microwave Background ◽  
Microwave Background Radiation ◽  
The Universe

Although the standard lambda cold dark matter cosmological model is quite successful in describing the universe, there are still several issues that are still not resolved. Some of these are the cosmological constant problem, certain anomalies in the cosmic microwave background radiation and whether general relativity is valid on large scales. Therefore, it is interesting to examine modified theories in an attempt to solve these problems, and to examine the entire range of possibilities that are allowed. In this work, we examine one of these modified theories, viz., f(R,T) gravity. We study the homogeneous and isotropic models in this theory, which have some pleasing features, such as no initial singularity, a dynamic cosmological term, and a transition from early deceleration to late-time acceleration as intimated by observations. The physical parameters of the model, as well as the energy conditions, are discussed and a viable cosmological model can be constructed.

Properties of the Dark Energy

2005 ◽  
Vol 201 ◽  
pp. 255-259
Author(s):  
Peter M. Garnavich ◽  
Yun. Wang
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Domain Walls ◽  
Accelerating Expansion ◽  
Systematic Effects ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

A non-zero cosmological constant is only one of many possible explanations for the observed accelerating expansion of the Universe. Any smoothly distributed, “dark” energy with a significant negative pressure can drive the acceleration. One possible culprit is a dynamical scalar field, but there are many less popular models such as tangled cosmic strings or domain walls. Soon theorists are likely to think up a number of new energies that can accelerate the expansion, meaning that only better observations can solve this question. Dark energy can be parameterized by its equation of state, w = p/ρ, which in the most general form can vary over time. Unlike the CMB, supernova observations cover a range of redshift so they can, in principle, probe the variation in the equation of state of the unknown component. The current SN observations loosely constrain the equation of state to w < −0.6, ruling out non-intercommuting strings and textures (w = −1/3), but consistent with a cosmological constant (w = −1). The constraints achievable from future large SN surveys are limited by our ability to understand systematic effects in SN Ia luminosities. But a large sample of supernovae reaching out to z ˜ 2 should at least discriminate between a cosmological constant and a dynamical scalar field as the source of the observed acceleration.

scholarly journals f (R) HO’RAVA-LIFSHITZ COSMOLOGIES VIA NOETER’S SYMMETRIES

2020 ◽  
Vol 70 (2) ◽  
pp. 177-182
Author(s):  
M.P. Imankul ◽  
◽  
Sh.R. Myrzakul ◽  
Keyword(s):  
Viscous Fluid ◽  
Cosmological Parameters ◽  
Viscous Fluids ◽  
Accelerated Expansion ◽  
Fermion Field ◽  
Accelerating Expansion ◽  
Fermion Fields ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

Wе іnvеstіgаtе thе gеnеrаl аpprоаch tо іndіng еxаct cоsmоlоgіcаl sоlutіоns in f (R) Hо’rаvа-Lіfshіtz grаvіtу, bаsеd оn Nоеthеrs thеоrеm. А fеаturе оf thіs аpprоаch іs thаt іt usеs thе bеhаvіоr оf аn еffеctіvе Lаgrаngіаn undеr іnіnіtеsіmаl trаnsfоrmаtіоns оf thе dеsіrеd sуmmеtrу, еxplіcіtlу dеtеrmіnіng thе fоrm f (R) fоr whіch such sуmmеtrіеs еxіst. Іt іs shоwn thаt thе dуnаmіcs оf thе scаlе fаctоr chаngеs аccоrdіng tо еіthеr а еxpоnеntіаl functіоn оf tіmе оr tо а pоwеr lаw. f-essence is one of generalized fermion fields. In this work, the dynamics of f-essence with a viscous fluid in the flat Friedmann-Robertson-Walker universe are studied. In addition, we analyzed various types of viscous fluids and investigated the possibility of reproducing the current accelerating expansion of the Universe. The cosmological parameters of this model are obtained. It shows that accelerated expansion can also be determined with a viscous fluid of the fermion field, as in the case of non-interacting perfect fluid considered in most modern models of accelerated expansion of the Universe.

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