scholarly journals Generalized F(R, T) cosmological models with fermionic fields

2021 ◽  
Vol 2090 (1) ◽  
pp. 012063
Author(s):  
Koblandy Yerzhanov ◽  
Gulnur Bauyrzhan ◽  
Ratbay Myrzakulov
Keyword(s):  
Mathematical Model ◽  
Cosmological Model ◽  
Main Idea ◽  
Scale Factor ◽  
Specific Form ◽  
Fermion Field ◽  
Fermionic Fields ◽  
Particular Solution ◽  
The Universe ◽  
Symmetry Method

Abstract We investigated the gravity model F (R, T), which interacts with a fermion field in a uniform and isotropic at spacetime FLRW. The main idea and purpose of the work donewas to create a mathematical model and find a particular solution for the scale factor a, since it describes the dynamics of the evolution of the Universe. The solutions for this universe are obtained using the Noether symmetry method. With its help, a specific form of the Lagrangian is obtained. And the possible types of the scale factor were found. The evolution of the resulting cosmological model has been investigated.

scholarly journals Cosmological model with fermion and tachyon fields interacting via Yukawa-type potential

2016 ◽  
Vol 31 (06) ◽  
pp. 1650039 ◽  
Author(s):  
Marlos O. Ribas ◽  
Fernando P. Devecchi ◽  
Gilberto M. Kremer
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Matter Field ◽  
Fermionic Field ◽  
Tachyonic Field ◽  
Fermionic Fields ◽  
The Universe ◽  
Type Potential

A model for the universe with tachyonic and fermionic fields interacting through a Yukawa-type potential is investigated. It is shown that the tachyonic field answers for the initial accelerated regime and for the subsequent decelerated regime so that it behaves as an inflaton at early times and as a matter field at intermediate times, while the fermionic field has the role of a dark energy constituent, since it leads to an accelerated regime at later times. The interaction between the fields via a Yukawa-type potential controls the duration of the decelerated era, since a stronger coupling makes a shorter decelerated period.

scholarly journals Anisotropic Bianchi Type-III Bulk Viscous Fluid Universe in Lyra Geometry

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Priyanka Kumari ◽  
M. K. Singh ◽  
Shri Ram
Keyword(s):  
Cosmological Model ◽  
Viscous Fluid ◽  
Bianchi Type ◽  
Lyra Geometry ◽  
Scale Factor ◽  
Field Equations ◽  
Type Iii ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
The Universe

An anisotropic Bianchi type-III cosmological model is investigated in the presence of a bulk viscous fluid within the framework of Lyra geometry with time-dependent displacement vector. It is shown that the field equations are solvable for any arbitrary function of a scale factor. To get the deterministic model of the universe, we have assumed that (i) a simple power-law form of a scale factor and (ii) the bulk viscosity coefficient are proportional to the energy density of the matter. The exact solutions of the Einstein’s field equations are obtained which represent an expanding, shearing, and decelerating model of the universe. Some physical and kinematical behaviors of the cosmological model are briefly discussed.

DENSITY PERTURBATIONS AND THE CHAPLYGIN GAS

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1674-1677
Author(s):  
SANDRO SILVA E COSTA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Power Spectrum ◽  
Cosmological Model ◽  
Chaplygin Gas ◽  
Scale Factor ◽  
Modified Chaplygin Gas ◽  
Modern Cosmology ◽  
Density Perturbations ◽  
The Universe

One approach in modern cosmology consists in supposing that dark matter and dark energy are different manifestations of a single 'quartessential' fluid. Following such idea, this work presents a summary of some studies of the evolution of density perturbations in a flat cosmological model with a modified Chaplygin gas acting as a single component. Our goal is to obtain properties of the model which can be used to distinguish it from another cosmological models which have the same solutions for the general evolution of the scale factor of the universe, even without the construction of the power spectrum. Both our analytical and numerical results clearly indicate as one interesting feature of the model the presence of peaks in the evolution of the density constrast.

scholarly journals DOES QUANTUM COSMOLOGY PREDICT A CONSTANT DILATONIC FIELD?

2005 ◽  
Vol 14 (02) ◽  
pp. 291-307 ◽  
Author(s):  
F. G. ALVARENGA ◽  
A. B. BATISTA ◽  
J. C. FABRIS
Keyword(s):  
Cosmological Model ◽  
Quantum Cosmology ◽  
Initial Conditions ◽  
Specific Model ◽  
Scale Factor ◽  
Gravitational Coupling ◽  
Expectation Values ◽  
Time Coordinate ◽  
Classical Models ◽  
The Universe

Quantum cosmology may permit to determine the initial conditions of the Universe. In particular, it may select a specific model between many possible classical models. In this work, we study a quantum cosmological model based on the string effective action coupled to matter. The Schutz's formalism is employed in the description of the fluid. A radiation fluid is considered. In this way, a time coordinate may be identified and the Wheeler–DeWitt equation reduces in the minisuperspace to a Schrödinger-like equation. It is shown that, under some quite natural assumptions, the expectation values indicate a null axionic field and a constant dilatonic field. At the same time the scale factor exhibits a bounce revealing a singularity-free cosmological model. In some cases, the mininum value of the scale factor can be related to the value of gravitational coupling.

scholarly journals Theory of Dark Matter and Dark Energy

2018 ◽  
Vol 10 (5) ◽  
pp. 1 ◽  
Author(s):  
Thierry Delort
Keyword(s):  
Mathematical Model ◽  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Model ◽  
Galaxy Clusters ◽  
Geometrical Model ◽  
New Model ◽  
Theoretical Predictions ◽  
The Mathematical Model ◽  
The Universe

In this article, we propose a new model of dark matter. According to this new model, dark matter is a substance, that is a new physical element not constituted of classical particles, called dark substance and filling the Universe. Assuming some very simple physical properties to this dark substance, we theoretically justify the flat rotation curve of galaxies and the baryonic Tully-Fisher’s law. We then study according to our new theory of dark matter  the different possible distributions of dark matter in galaxies and in galaxy clusters, and the velocities of galaxies in galaxy clusters. Then using the new model of dark matter we are naturally led to propose a new geometrical model of Universe, finite, that is different from all geometrical models proposed by the Standard Cosmological Model (SCM). Despite that our Theory of dark matter is compatible with the SCM, we then expose a new Cosmological model based on this new geometrical form of the Universe and on the interpretation of the CMB Rest Frame (CRF), that has not physical interpretation on the SCM and that we will call local Cosmological frame. We then propose 2 possible mathematical models of expansion inside the new Cosmological model. The 1st mathematical model is based on General Relativity as the SCM and gives the same theoretical predictions of distances and of the Hubble’s constant as the SCM. The 2nd mathematical model of expansion of the Universe is mathematically much simpler than the mathematical model of expansion used in the SCM, but we will see that its theoretical predictions are in agreement with astronomical observations. Moreover, this 2nd mathematical model of expansion does not need to introduce the existence of a dark energy contrary to the mathematical model of expansion of the SCM. To end we study the evolution of the temperature of dark substance in the Universe and we make appear the existence of a dark energy, due to our model of dark matter.

Cosmological spacetimes

2018 ◽  
Author(s):  
Nathalie Deruelle ◽  
Jean-Philippe Uzan
Keyword(s):  
Cosmological Model ◽  
Large Scale ◽  
Cosmic Time ◽  
De Sitter ◽  
Matter Distribution ◽  
Observable Universe ◽  
Cosmological Principle ◽  
Riemannian Spacetime ◽  
The Universe ◽  
Copernican Principle

This chapter provides a few examples of representations of the universe on a large scale—a first step in constructing a cosmological model. It first discusses the Copernican principle, which is an approximation/hypothesis about the matter distribution in the observable universe. The chapter then turns to the cosmological principle—a hypothesis about the geometry of the Riemannian spacetime representing the universe, which is assumed to be foliated by 3-spaces labeled by a cosmic time t which are homogeneous and isotropic, that is, ‘maximally symmetric’. After a discussion on maximally symmetric space, this chapter considers spacetimes with homogenous and isotropic sections. Finally, this chapter discusses Milne and de Sitter spacetimes.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

scholarly journals IMPLICATIONS OF A QUANTUM MECHANICAL TREATMENT OF THE UNIVERSE

1998 ◽  
Vol 13 (05) ◽  
pp. 347-351 ◽  
Author(s):  
MURAT ÖZER
Keyword(s):  
Quantum Mechanics ◽  
Wave Packet ◽  
Early Universe ◽  
Mechanical Treatment ◽  
Correspondence Principle ◽  
Scale Factor ◽  
Quantum Mechanical ◽  
Quantum Mechanical Treatment ◽  
The Standard Model ◽  
The Universe

We attempt to treat the very early Universe according to quantum mechanics. Identifying the scale factor of the Universe with the width of the wave packet associated with it, we show that there cannot be an initial singularity and that the Universe expands. Invoking the correspondence principle, we obtain the scale factor of the Universe and demonstrate that the causality problem of the standard model is solved.

Marketing Fraud: An Approach for Differentiating Multilevel Marketing from Pyramid Schemes

2002 ◽  
Vol 21 (1) ◽  
pp. 139-151 ◽  
Author(s):  
Peter J. Vander Nat ◽  
William W. Keep
Keyword(s):  
Mathematical Model ◽  
Distribution Channel ◽  
Specific Form ◽  
The Internet ◽  
Key Factors ◽  
Direct Selling ◽  
Multilevel Marketing ◽  
International Growth ◽  
Pyramid Scheme ◽  
Pyramid Schemes

A specific form of direct selling, multilevel marketing (MLM), experienced significant international growth during the 1990s, facilitated in part by the development of the Internet. A corresponding increase in the investigation and prosecution of illegal pyramid schemes occurred during the same period. These parallel activities led to increased uncertainty among marketing managers who used or wished to use the MLM approach. The authors examine similarities between the multilevel approach to marketing and activities associated with illegal pyramid schemes. A mathematical model is used to differentiate between the two on the basis of previous pyramid scheme cases and current U.S. law. The results of the model suggest key factors that marketers interested in MLM will need to consider when developing this type of distribution channel.

Southeast Asian Muslim Washathyyah in the Global Era

2015 ◽  
Vol 4 (1) ◽  
pp. 137-154
Author(s):  
Syahrin Harahap
Keyword(s):  
Southeast Asia ◽  
Significant Contribution ◽  
Main Idea ◽  
Global Village ◽  
Global Era ◽  
The People ◽  
The World ◽  
Huge Impact ◽  
Religious Aspects ◽  
The Universe

Globalization in the world has given the huge impact on the people, as the new condition of the world has brought the world to the globalism- a consciousness and understanding that the world is one. Globalization has also unified the people in a global village that covers all aspects of life such as economic, political, cultural, religious aspects. This paper will explore the concept of wa¡a¯iyyah which stresses on the moderation and accommodative way and its implementation in Southeast Asia. The main idea of the wa¡a¯iyyah or moderation in religious life is that it offers the importance of realizing the concept of Islamic blessing for all the Universe (Islam; Ra¥matan lil ±lam³n). Therefore, the main offer of the Muslim wa¡a¯iyyah movement is to focus on developing civilization, freedom, justice, prosperity and better future for all the people. It is the main capital of the Wa¡a¯iyyah in Southeast Asia to give the significant contribution to the globalization of the world.

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