scholarly journals Cosmological Einstein–Maxwell model with g-essence

2019 ◽  
Vol 28 (10) ◽  
pp. 1950126 ◽  
Author(s):  
Olga Razina ◽  
Pyotr Tsyba ◽  
Bekdaulet Meirbekov ◽  
Ratbay Myrzakulov
Keyword(s):  
Maxwell Model ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Four Dimensions ◽  
Fermion Fields ◽  
Walker Metric ◽  
Expansion Of The Universe ◽  
Boson Fields ◽  
Model Independent ◽  
Specific Equation

In this paper, we study the model of the late universe with the homogeneous, isotropic and flat Friedmann–Robertson–Walker metric, where the source of the gravitational field is based on the fermion and boson fields, with the Maxwell term [Formula: see text] in four dimensions. The actuation of the Maxwell term for the Einstein gravity makes it possible to find new approaches to solve the problem of the observed accelerated expansion of the universe. Energy conditions have been obtained and studied. These conditions impose very simple and model-independent restrictions on the behavior of energy density and pressure since they do not require a specific equation-of-state of matter. To consider the model, the energy conditions NEC, WEC, DEC are realized, and the SEC condition is violated. The boson and fermion fields are responsible for the accelerated regime at early times, but since the total pressure tends toward zero for large times, a transition to a decelerated regime occurs. Maxwell field is crucial only in the early times.

ROLE OF EXTRA DIMENSION IN ACCELERATED EXPANSION

2008 ◽  
Vol 23 (06) ◽  
pp. 909-917 ◽  
Author(s):  
K. D. PUROHIT ◽  
YOGESH BHATT
Keyword(s):  
Cosmological Model ◽  
Extra Dimension ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Four Dimensions ◽  
Scale Factors ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Kaluza Klein

A five-dimensional FRW-type Kaluza–Klein cosmological model is taken to study the role of extra dimension in the expansion of the universe. Relation between scale factors corresponding to conventional four dimensions and the extra dimension has been established. Field equations are solved in order to find out the effect of pressure corresponding to these scale factors. Conditions for accelerated expansion are derived.

scholarly journals Observational constraints and stability in viscous gravity

2020 ◽  
Vol 98 (12) ◽  
pp. 1119-1124
Author(s):  
T. Mirzaei Rezaei ◽  
Alireza Amani ◽  
E. Yusofi ◽  
S. Rouhani ◽  
M.A. Ramzanpour
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Teleparallel Gravity ◽  
System Stability ◽  
Accelerated Expansion ◽  
Tetrad Field ◽  
Dark Energy Component ◽  
Walker Metric ◽  
Expansion Of The Universe ◽  
The Universe

In this paper, we study the [Formula: see text] gravity model in the presence of bulk viscosity by the flat Friedmann–Robertson–Walker metric. The field equation is obtained by teleparallel gravity with a tetrad field. The universe components are considered matter and dark energy, with the dark energy component associated with viscous [Formula: see text] gravity. After calculating the Friedmann equations, we obtain the energy density, pressure, and equation of state of dark energy in terms of the redshift parameter. Afterward, we plot the corresponding cosmological parameters versus the redshift parameter and examine the accelerated expansion of the universe. In the end, we explore the system stability using a function called the speed sound parameter.

scholarly journals ON ANISOTROPIC DARK ENERGY

2009 ◽  
Vol 24 (14) ◽  
pp. 1137-1146 ◽  
Author(s):  
R. CHAN ◽  
M. F. A. DA SILVA ◽  
JAIME F. VILLAS DA ROCHA
Keyword(s):  
Dark Energy ◽  
Careful Analysis ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Anisotropic Pressure ◽  
Anisotropic Dark Energy ◽  
Isotropic Pressure ◽  
Expansion Of The Universe ◽  
Standard Cosmological Model ◽  
The Universe

Since the discovery of accelerated expansion of the universe, it was necessary to introduce a new component of matter distribution called dark energy. The standard cosmological model considers isotropy of the pressure and assumes an equation of state p = ωρ, relating the pressure p and the energy density ρ. The interval of the parameter ω defines the kind of matter of the universe, related to the fulfillment, or not, of the energy conditions of the fluid. The recent interest in this kind of fluid with anisotropic pressure, in the scenario of the gravitational collapse and star formation, imposes a careful analysis of the energy conditions and the role of the components of the pressure. Here, in this work, we show an example where the classification of dark energy for isotropic pressure fluids is used incorrectly for anisotropic fluids. The correct classification and its consequences are presented.

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.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

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.

INFLATION, QUINTESSENCE PROBLEM AND VARYING SPEED OF LIGHT

2002 ◽  
Vol 17 (05) ◽  
pp. 295-302
Author(s):  
SUBENOY CHAKRABORTY
Keyword(s):  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Speed Of Light ◽  
Expansion Of The Universe ◽  
The Universe

In this paper it is shown that the present accelerated expansion of the Universe can be explained only by considering variation of the speed of light, without taking into account the cosmological constant or quintessence matter.

Heuristic determination of the cosmological constant

2021 ◽  
pp. 2150114
Author(s):  
Manuel Urueña Palomo ◽  
Fernando Pérez Lara
Keyword(s):  
Field Theory ◽  
Energy Density ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Fundamental Constants ◽  
Quantum Field ◽  
Brute Force ◽  
Expansion Of The Universe ◽  
The Universe

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

scholarly journals Can accelerated expansion of the universe be due to spacetime vorticity?

2018 ◽  
Vol 33 (40) ◽  
pp. 1850240
Author(s):  
Babur M. Mirza
Keyword(s):  
Magnetic Field ◽  
Accelerated Expansion ◽  
Newtonian Gravity ◽  
Hubble’S Parameter ◽  
Cosmic Expansion ◽  
Zero Curvature ◽  
Expansion Of The Universe ◽  
General Relativistic ◽  
The Universe ◽  
The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

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