scholarly journals Inflation from the Symmetry of the Generalized Cosmological Model

Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2254
Author(s):  
Koblandy Yerzhanov ◽  
Gulnur Bauyrzhan ◽  
Aziza Altaibayeva ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Power Law ◽  
Kinetic Term ◽  
Inflationary Model ◽  
Power Law Model ◽  
Lagrange Equations ◽  
Similar Time ◽  
Starobinsky Model ◽  
Monge Ampere

It is shown that the inflationary model is the result of the symmetry of the generalized F(R,T,X,φ)-cosmological model using the Noether symmetry. It leads to a solution, a particular case of which is Starobinsky’s cosmological model. It is shown that even in the more particular case of cosmological models F(R,X,φ) and F(T,X,φ) the Monge–Ampère equation is still obtained, one of the solutions including the Starobinsky model. For these models, it is shown that one can obtain both power-law and exponential solutions for the scale factor from the Euler–Lagrange equations. In this case, the scalar field φ has similar time dependences, exponential and exponential. The resulting form of the Lagrangian of the model allows us to consider it as a model with R2 or X2. However, it is also shown that previously less studied models with a non-minimal relationship between R and X are important, as one of the possible models. It is shown that in this case the power-law model can have a limited evolutionary period with a negative value of the kinetic term.

scholarly journals COSMOLOGICAL DYNAMICS OF f(R) GRAVITY SCALAR DEGREE OF FREEDOM IN EINSTEIN FRAME

2013 ◽  
Vol 22 (14) ◽  
pp. 1350083 ◽  
Author(s):  
UMANANDA DEV GOSWAMI ◽  
KABITA DEKA
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Einstein Frame ◽  
Degree Of Freedom ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Power Law Model ◽  
Starobinsky Model ◽  
Expansion Of The Universe ◽  
The Universe

f(R) gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as a manifestation of the large scale modification of the force of gravity. f(R) gravity models can be expressed in terms of a scalar degree of freedom by redefinition of model's variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law (ξRn) and the Starobinsky (disappearing cosmological constant) f(R) gravity models numerically in the Einstein frame. Both the models show interesting behavior of their scalar degree of freedom and could produce the accelerated expansion of the universe in the Einstein frame with the negative equation of state of the scalar field. However, the scalar field potential for the power-law model is the well-behaved function of the field, whereas the potential becomes flat for higher value of field in the case of the Starobinsky model. Moreover, the equation of state of the scalar field for the power-law model is always negative and less than -1/3, which corresponds to the behavior of the dark energy, that produces the accelerated expansion of the universe. This is not always the case for the Starobinsky model. At late times, the Starobinsky model behaves as cosmological constant Λ as behaves by power-law model for the values of n → 2 at all times.

scholarly journals Light of Planck-2015 on Noncanonical Inflation

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Kh. Saaidi ◽  
A. Mohammadi ◽  
T. Golanbari
Keyword(s):  
Scalar Field ◽  
Observational Data ◽  
Power Law ◽  
Hubble Parameter ◽  
Field Model ◽  
Kinetic Term ◽  
Inflationary Scenario ◽  
Slow Roll ◽  
Power Law Function ◽  
Free Parameters

Slow-roll inflationary scenario is considered in noncanonical scalar field model supposing a power-law function for kinetic term and using two formalisms. In the first approach, the potential is picked out as a power-law function, that is, the most common approach in studying inflation. Hamilton-Jacobi approach is selected as the second formalism, so that the Hubble parameter is introduced as a function of scalar field instead of the potential. Employing the last observational data, the free parameters of the model are constrained, and the predicted form of the potential and attractor behavior of the model are studied in detail.

Tachyon scalar field in a braneworld cosmology

2018 ◽  
Vol 33 (34) ◽  
pp. 1845017 ◽  
Author(s):  
Dragoljub D. Dimitrijevic ◽  
Neven Bilić ◽  
Goran S. Djordjevic ◽  
Milan Milosevic ◽  
Marko Stojanovic
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Power Law ◽  
Inverse Power ◽  
Warp Factor ◽  
Braneworld Cosmology ◽  
Model Based ◽  
Inverse Power Law ◽  
Cosmological Context

We analyze a tachyon cosmological model based on the dynamics of a 3-brane in the bulk of the second Randall–Sundrum model. This model contains extended general warp functions, i.e. generalized bulk geometry. We study a power law warp factor in cosmological context. This type of warp factor generates an inverse power law tachyonic potential.

scholarly journals LRS Bianchi Type-I Inflationary String Cosmological Model in Brans-Dicke Theory of Gravitation

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
R. Venkateswarlu ◽  
J. Satish
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Power Law ◽  
Bianchi Type ◽  
Type I ◽  
Physical Behavior ◽  
Bianchi Type I ◽  
Expansion Scalar ◽  
Theory Of Gravitation ◽  
Shear Scalar

We investigate locally rotational symmetric (LRS) Bianchi type I space time coupled with scalar field. String cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We assume that the expansion scalar is proportional to the shear scalar and also power law ansatz for scalar field. The physical behavior of the resulting model is discussed through different parameters.

scholarly journals Anisotropic power-law inflation in a two-scalar-field model with a mixed kinetic term

2017 ◽  
Vol 26 (07) ◽  
pp. 1750072 ◽  
Author(s):  
Tuan Q. Do ◽  
Sonnet Hung Q. Nguyen
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Field Model ◽  
Scalar Fields ◽  
Kinetic Term ◽  
Type I ◽  
Field Equations ◽  
Scalar Field Model ◽  
Phantom Scalar ◽  
The Stability

We examine whether an extended scenario of a two-scalar-field model, in which a mixed kinetic term of canonical and phantom scalar fields is involved, admits the Bianchi type I metric, which is homogeneous but anisotropic spacetime, as its power-law solutions. Then, we analyze the stability of the anisotropic power-law solutions to see whether these solutions respect the cosmic no-hair conjecture or not during the inflationary phase. In addition, we will also investigate a special scenario, where the pure kinetic terms of canonical and phantom fields disappear altogether in field equations, to test again the validity of cosmic no-hair conjecture. As a result, the cosmic no-hair conjecture always holds in both these scenarios due to the instability of the corresponding anisotropic inflationary solutions.

QUANTUM FLUCTUATIONS AND ETERNAL INFLATION IN THE R2MODEL

1988 ◽  
Vol 03 (03) ◽  
pp. 617-629 ◽  
Author(s):  
DAVID H. COULE ◽  
MILAN B. MIJIĆ
Keyword(s):  
Random Walk ◽  
Scalar Field ◽  
Power Law ◽  
Quantum Fluctuations ◽  
Global Structure ◽  
Inflationary Model ◽  
Field Case ◽  
Standard Cosmology ◽  
Eternal Inflation ◽  
The Universe

We show that in the R2 inflationary model, as in the scalar field case, quantum fluctuations at early times can be sufficiently large that the universe evolves like a random walk. Within this picture we describe the resulting global structure of the universe: the so-called “eternal inflation” scenario. Such behavior can naturally fit into a picture of “quantum creation of the universe”. Inflating domains are present today and in fact are growing in number. Approximately every 10−31 s new hot radiation dominated domains are created which occupy a volume larger than all the previously existing Friedmann universes; during the first ~10−9 fraction of this period the power law expanding volume exceeds the inflating volume. Regularly, numerous domains occur where inflation proceeds purely classically and sufficiently to solve the problems of standard cosmology.

Multi-scalar field cosmological model and possible solutions using Noether symmetry approach

2021 ◽  
Author(s):  
Santu Mondal ◽  
Roshni Bhaumik ◽  
Sourav Dutta ◽  
Subenoy Chakraborty
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Potential Function ◽  
Evolution Equations ◽  
Scalar Fields ◽  
Noether Symmetry ◽  
Kinetic Term ◽  
View Point ◽  
Symmetry Approach ◽  
Augmented Space

In this work, a cosmological model is considered having two scalar fields minimally coupled to gravity with a mixed kinetic term. The model is characterized by the coupling function and the potential function which are assumed to depend on one of the scalar fields. Instead of choosing these functions phenomenologically here, they are evaluated assuming the existence of Noether symmetry. By appropriate choice of a point transformation in the augmented space, one of the variables in the Lagrangian becomes cyclic and the evolution equations become much simpler to have solutions. Finally, the solutions are analyzed from cosmological view point.

scholarly journals A New Solution of Intermediate Cosmological Inflation with the Effect of Scalar Field

2021 ◽  
Vol 41 (1) ◽  
pp. 112-121
Author(s):  
Shomi Aktar ◽  
Anjan Kumar Chowdhury
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Equation Of Motion ◽  
Rapid Expansion ◽  
Inflationary Universe ◽  
Inflationary Model ◽  
Cosmological Inflation ◽  
The Universe ◽  
Interior Solutions

According to the inflationary model, the universe had a brief period of extraordinarily rapid expansion or inflation during which its diameter increased by a factor at least 1025 times larger than previously thought. In this work an analysis is given on inflationary universe, which expands at a rate intermediate between that of power-law and exponential inflation. We have examined the model of Barrow which is solved exactly and leaded to power law inflation. We have tested a new potential by applying the scalar field using the equation of motion and found some new interior solutions. The Chittagong Univ. J. Sci. 40(1) : 112-121, 2019

scholarly journals Cosmological reconstruction and energy constraints in generalized Gauss–Bonnet-scalar–kinetic–matter couplings

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Adam Z. Kaczmarek ◽  
Dominik Szczęśniak
Keyword(s):  
Scalar Field ◽  
Perfect Fluid ◽  
Power Law ◽  
Cosmological Models ◽  
Energy Conditions ◽  
Kinetic Term ◽  
De Sitter ◽  
Field Equations ◽  
Energy Constraints ◽  
Matter Fields

Abstract Recently introduced $$f(\mathcal {G},T)$$ f ( G , T ) theory is generalized by adding dependence on the arbitrary scalar field $$\phi $$ ϕ and its kinetic term $$(\nabla \phi )^2$$ ( ∇ ϕ ) 2 , to explore non-minimal interactions between geometry, scalar and matter fields in context of the Gauss–Bonnet theories. The field equations for the resulting $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T theory are obtained and show that particles follow non-geodesic trajectories in a perfect fluid surrounding. The energy conditions in the Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime are discussed for the generic function $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T . As an application of the introduced extensions, using the reconstruction techniques we obtain functions that satisfy common cosmological models, along with the equations describing energy conditions for the reconstructed $$f\left( \mathcal {G},\phi ,(\nabla \phi )^2,T\right) $$ f G , ϕ , ( ∇ ϕ ) 2 , T gravity. The detailed discussion of the energy conditions for the de Sitter and power-law spacetimes is provided in terms of the fixed kinetic term i.e. in the $$f\left( \mathcal {G},\phi ,T\right) $$ f G , ϕ , T case. Moreover, in order to check viability of the reconstructed models, we discuss the energy conditions in the specific cases, namely the $$f(R,\phi ,(\nabla \phi )^2)$$ f ( R , ϕ , ( ∇ ϕ ) 2 ) and $$f=\gamma (\phi ,X)\mathcal {G}+\mu T^{1/2}$$ f = γ ( ϕ , X ) G + μ T 1 / 2 approaches. We show, that for the appropriate choice of parameters and constants, the energy conditions can be satisfied for the discussed scenarios.

scholarly journals Intermediate Inflation or Late Time Acceleration?

2008 ◽  
Vol 2008 ◽  
pp. 1-16 ◽  
Author(s):  
Abhik Kumar Sanyal
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Cosmological Evolution ◽  
Expansion Rate ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Late Time ◽  
Late Time Acceleration ◽  
Cosmic Evolution ◽  
Scaling Solution

The expansion rate of “intermediate inflation” lies between the exponential and power law expansion but corresponding accelerated expansion does not start at the onset of cosmological evolution. Present study of “intermediate inflation” reveals that it admits scaling solution and has got a natural exit form it at a later epoch of cosmic evolution, leading to late time acceleration. The corresponding scalar field responsible for such feature is also found to behave as a tracker field for gravity with canonical kinetic term.

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