Inflationary cosmology for f(R, ϕ) models with different potentials

2017 ◽  
Vol 95 (11) ◽  
pp. 1074-1085 ◽  
Author(s):  
M. Zubair ◽  
Farzana Kousar
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Energy Density ◽  
Cosmological Constant ◽  
Observational Data ◽  
Power Law ◽  
Early Time ◽  
Inflationary Cosmology ◽  
Effective Equation ◽  
Slow Roll

We examine inflation in [Formula: see text] theory, where a scalar field is coupled to gravity. We have constructed [Formula: see text] models using exponential and power law potentials and study inflation for these models, which can support the early-time acceleration with a useful cosmological constant at high curvature. We have calculated the slow-roll parameters, scalar-to-tensor ratio, and spectral index for these models and analyzed them graphically to check the viability according to recent observational data. We have also presented the evolution of effective equation of state and energy density.

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.

scholarly journals Cosmological constant in chameleon Brans–Dicke theory

2019 ◽  
Vol 28 (01) ◽  
pp. 1950022 ◽  
Author(s):  
Yousef Bisabr
Keyword(s):  
Exact Solution ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Exact Solutions ◽  
Effective Mass ◽  
Potential Function ◽  
Power Law ◽  
Exponential Form ◽  
First Case ◽  
Different Types

We consider a generalized Brans–Dicke model in which the scalar field has a self-interacting potential function. The scalar field is also allowed to couple nonminimally with the matter part. We assume that it has a chameleon behavior in the sense that it acquires a density-dependent effective mass. We consider two different types of matter systems which couple with the chameleon, dust and vacuum. In the first case, we find a set of exact solutions when the potential has an exponential form. In the second case, we find a power-law exact solution for the scale factor. In this case, we will show that the vacuum density decays during expansion due to coupling with the chameleon.

scholarly journals Exact and Slow-Roll Solutions for Exponential Power-Law Inflation Connected with Modified Gravity and Observational Constraints

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 199
Author(s):  
Igor Fomin ◽  
Sergey Chervon
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Hubble Parameter ◽  
Gravity Models ◽  
Observational Constraints ◽  
Slow Roll ◽  
Correct Model ◽  
Scalar Spectral Index ◽  
Wide Range ◽  
Exponential Power

We investigate the ability of the exponential power-law inflation to be a phenomenologically correct model of the early universe. We study General Relativity (GR) scalar cosmology equations in Ivanov–Salopek–Bond (or Hamilton–Jacobi like) representation where the Hubble parameter H is the function of a scalar field ϕ. Such approach admits calculation of the potential for given H(ϕ) and consequently reconstruction of f(R) gravity in parametric form. By this manner the Starobinsky potential and non-minimal Higgs potential (and consequently the corresponding f(R) gravity) were reconstructed using constraints on the model’s parameters. We also consider methods for generalising the obtained solutions to the case of chiral cosmological models and scalar-tensor gravity. Models based on the quadratic relationship between the Hubble parameter and the function of the non-minimal interaction of the scalar field and curvature are also considered. Comparison to observation (PLANCK 2018) data shows that all models under consideration give correct values for the scalar spectral index and tensor-to-scalar ratio under a wide range of exponential-power-law model’s parameters.

On braneworld inverse power-law inflation

2018 ◽  
Vol 33 (10) ◽  
pp. 1850058 ◽  
Author(s):  
H. Es-sobbahi ◽  
M. Nach
Keyword(s):  
Observational Data ◽  
Power Law ◽  
Equations Of Motion ◽  
High Energy ◽  
Type Ii ◽  
Scalar Model ◽  
Slow Roll ◽  
Inverse Power Law ◽  
Perturbation Spectrum ◽  
High Energy Regime

In the framework of the braneworld Randall–Sundrum type II model, we investigate an inflationary scalar model in the high-energy regime. In this regime, the slow-roll parameters and the perturbation spectrum of the model are derived. The corresponding results are dealt with according to the known observational data. Then the solutions to the equations of motion on the brane are given.

scholarly journals Chameleon field dynamics during inflation

2018 ◽  
Vol 27 (04) ◽  
pp. 1850041 ◽  
Author(s):  
Nasim Saba ◽  
Mehrdad Farhoudi
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Big Bang ◽  
Late Time ◽  
Inflationary Model ◽  
Slow Roll ◽  
Equation Of State Parameter ◽  
The Common ◽  
The Universe

By studying the chameleon model during inflation, we investigate whether it can be a successful inflationary model, wherein we employ the common typical potential usually used in the literature. Thus, in the context of the slow-roll approximations, we obtain the e-folding number for the model to verify the ability of resolving the problems of standard big bang cosmology. Meanwhile, we apply the constraints on the form of the chosen potential and also on the equation of state parameter coupled to the scalar field. However, the results of the present analysis show that there is not much chance of having the chameleonic inflation. Hence, we suggest that if through some mechanism the chameleon model can be reduced to the standard inflationary model, then it may cover the whole era of the universe from the inflation up to the late time.

scholarly journals HOLOGRAPHIC DARK ENERGY MODEL CHARACTERIZED BY THE CONFORMAL-AGE-LIKE LENGTH

2012 ◽  
Vol 27 (16) ◽  
pp. 1250085 ◽  
Author(s):  
ZHUO-PENG HUANG ◽  
YUE-LIANG WU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Dimensional Space ◽  
Early Time ◽  
Energy Model ◽  
Holographic Dark Energy Model ◽  
Frw Universe

A holographic dark energy model characterized by the conformal-age-like length scale [Formula: see text] is motivated from the four-dimensional space–time volume at cosmic time t in the flat Friedmann–Robertson–Walker (FRW) universe. It is shown that when the background constituent with constant equation of state wm dominates the universe in the early time, the fractional energy density of the dark energy scales as [Formula: see text] with the equation of state given by [Formula: see text]. The value of wm is taken to be wm≃-1 during inflation, wm = ⅓ in radiation-dominated epoch and wm = 0 in matter-dominated epoch, respectively. When the model parameter d takes the normal value at order one, the fractional density of dark energy is naturally negligible in the early universe, Ω de ≪1 at a ≪1. With such an analytic feature, the model can be regarded as a single-parameter model like the ΛCDM model, so that the present fractional energy density Ω de (a = 1) can solely be determined by solving the differential equation of Ωde once d is given. We further extend the model to the general case in which both matter and radiation are present. The scenario involving possible interaction between the dark energy and the background constituent is also discussed.

scholarly journals On a Slightly Different Power Law-Scaling for the Flat Universe

2020 ◽  
Vol 12 (4) ◽  
pp. 569-574
Author(s):  
C. Sivakumar ◽  
R. Francis
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Power Law ◽  
Hubble Parameter ◽  
State Parameter ◽  
Effective Equation ◽  
Flat Universe ◽  
Equation Of State Parameter ◽  
Age Of The Universe ◽  
The Universe

A slightly different power law-scaling fits to the picture of our 13.7 billion years old flat universe which is expanding presently at 67 km/s/Mpc with an acceleration. The model which is an attempt to retain power-law scaling in the light of the accepted facts about the universe we are living in, has a constant effective equation of state parameter as the cosmic fluid is a solution of matter, radiation and dark energy. It is successful in explaining the acceleration of universe which the normal power law fails if the present Hubble parameter is 67 km/s/Mpc and age of the universe is 13.7 billion years, and it is free from the defect of singularity.

scholarly journals Viscous coupled fluids in terms of a log-corrected equation-of-state

2021 ◽  
Vol 18 (12) ◽  
Author(s):  
I. Brevik ◽  
K. Myrzakulov ◽  
A. V. Timoshkin ◽  
A. Zhadyranova
Keyword(s):  
Dark Matter ◽  
Comparative Analysis ◽  
Equation Of State ◽  
Energy Density ◽  
Power Law ◽  
Late Time ◽  
System Of Equations ◽  
Power Law Fluid ◽  
Power Law Equation ◽  
Detailed Picture

In this paper, we consider a class of cosmological fluids that possess properties analogous to those of crystalline solids undergoing isotropic deformations. Our research is based on a modified log-corrected power-law equation of state in the presence of a bulk viscosity. This formalism represents a class of the so-called logotropic fluids, and allows explaining an accelerating late-time universe. In order to obtain a more detailed picture of its evolution, we add in our model a coupling of the log-corrected power-law fluid to dark matter, and study various interacting forms between them. We solve the system of equations for a modified log-power-law fluid coupled to dark matter, and obtain expressions for the log-corrected power-law energy density, and the energy density for dark matter. A comparative analysis is made with the model of a nonviscous log-corrected power-law fluid without interaction with dark matter.

scholarly journals Unrivaled quantum vacuum in the primordial universe

2021 ◽  
Vol 36 (01) ◽  
pp. 2150002
Author(s):  
Davood Momeni
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Effective Mass ◽  
Conformal Symmetry ◽  
Early Time ◽  
Late Time ◽  
Quantization Scheme ◽  
Quantum Vacuum ◽  
Vacuum States ◽  
Dominant Part

In a primordial universe pre- (post-)inflationary era, there could be phases of early universe made of cold gas baryons, radiation and early post-inflationary cosmological constant. I showed that in the baryonic epoch, the quantum vacuum is unique. By using the standard quantization scheme for a massive minimally coupled scalar field with maximal conformal symmetry in the classical space–time, I demonstrated that the scalar modes had an effective mass [Formula: see text] (or [Formula: see text]). This argument was validated when the conformal time [Formula: see text] kept so close to the inflation ending time [Formula: see text]. The energy density of the baryonic matter diverged at the inflation border and vanishes at the late time future. Furthermore, I argued that at very early accelerating epoch when the radiation was the dominant part in the close competition with the early time cosmological constant, fine-tuned mass of the scalar field [Formula: see text] also provided a unique quantum vacuum. The reason is that the effective mass eventually is vanished. A remarkable observation was that all the other possible vacuum states “squeezed” eternally.

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