scholarly journals Inflation constraints for classes of f(R) models

2018 ◽  
Vol 15 (12) ◽  
pp. 1850209
Author(s):  
Joseph Ntahompagaze ◽  
Jean Damascène Mbarubucyeye ◽  
Shambel Sahlu ◽  
Amare Abebe
Keyword(s):  
Scalar Field ◽  
Early Universe ◽  
First Derivative ◽  
A Value ◽  
Slow Roll ◽  
Theories Of Gravity ◽  
Text Model ◽  
Definition Of ◽  
Inflationary Parameters

In this paper, we explore the equivalence between two theories, namely [Formula: see text] and scalar–tensor theories of gravity. We use this equivalence to explore several [Formula: see text] toy models focusing on the inflation epoch of the early universe. The study is done based on the definition of the scalar field in terms of the first derivative of [Formula: see text] model. We have applied the slow-roll approximations during inflationary parameters consideration. The comparison of the numerically computed inflationary parameters with the observations is done. We have inspected that some of the [Formula: see text] models produce numerical values of [Formula: see text] that are in the same range as the suggested values from observations. But for the case of the tensor-to-scalar ratio [Formula: see text], we realized that some of the considered [Formula: see text] models suffer to produce a value which is in agreement with the observed values for different considered space parameter.

Investigating inflation driven by DBI-essence scalar field

2020 ◽  
Vol 29 (12) ◽  
pp. 2050087
Author(s):  
Gargee Chakraborty ◽  
Surajit Chattopadhyay
Keyword(s):  
Scalar Field ◽  
Early Universe ◽  
Inflationary Model ◽  
Type Iii ◽  
Ultraviolet Cutoff ◽  
Big Rip ◽  
Slow Roll ◽  
Limiting Case

Motivated by the work of Nojiri et al., Phys. Lett. B 797, 134829 (2019), the present study demonstrates inflation driven by holographic DBI-essence scalar field. Considering a simple correction due to the Ultraviolet cutoff, we have studied the slow-roll parameters. It has been observed that the role of the UV-cutoff is not negligible and in the limiting case of [Formula: see text] the inflationary model is characterized by Type-III singularity but can avoid Big-Rip singularity. Finally, it has been observed that the trajectories in [Formula: see text] are compatible with the observational bound found by Planck. It has been concluded that the tensor to scalar ratio for this model can explain the primordial fluctuation in the early universe as well. However, under the purview of [Formula: see text] inflation, although the DBI-essence scalar field can explain primordial fluctuation, the holographic DBI-essence scalar field does not lead to [Formula: see text] trajectory satisfying the Planck’s observational bound.

scholarly journals Dynamics of tachyon fields and inflation - comparison of analytical and numerical results with observation

2016 ◽  
pp. 1-8 ◽  
Author(s):  
M. Milosevic ◽  
D.D. Dimitrijevic ◽  
G.S. Djordjevic ◽  
M.D. Stojanovic
Keyword(s):  
Scalar Field ◽  
String Theory ◽  
Numerical Methods ◽  
Spectral Index ◽  
Early Universe ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
Homogeneous Universe ◽  
The Given ◽  
Good Agreement

The role tachyon fields may play in evolution of early universe is discussed in this paper. We consider the evolution of a flat and homogeneous universe governed by a tachyon scalar field with the DBI-type action and calculate the slow-roll parameters of inflation, scalar spectral index (n), and tensor-scalar ratio (r) for the given potentials. We pay special attention to the inverse power potential, first of all to V (x) ~ x?4, and compare the available results obtained by analytical and numerical methods with those obtained by observation. It is shown that the computed values of the observational parameters and the observed ones are in a good agreement for the high values of the constant X0. The possibility that influence of the radion field can extend a range of the acceptable values of the constant X0 to the string theory motivated sector of its values is briefly considered.

Inflationary dynamics in f(𝒢) gravity

2017 ◽  
Vol 26 (04) ◽  
pp. 1750030 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Power Spectrum ◽  
Universe Model ◽  
De Sitter ◽  
Slow Roll ◽  
Homogeneous Universe ◽  
Text Model ◽  
Flow Functions ◽  
Hubble Flow

This paper investigates inflationary dynamics for isotropic and homogeneous universe model in the background of [Formula: see text] gravity. We construct Hubble-flow functions, slow-roll parameters, amplitude of scalar power spectrum, spectral index and tensor–scalar ratio for a particular form of equation of state which describes quasi-de Sitter expansion. The dynamics of inflationary epoch is analyzed for scalar field as well as fluid cosmology with viable power-law [Formula: see text] model. We obtain different potential functions that correspond to chaotic inflation and Starobinsky type models. The graphical behavior of these parameters shows compatible results with observational Planck 2015 data in this gravity.

Shaft potential inspired warm inflation

2017 ◽  
Vol 14 (06) ◽  
pp. 1750088 ◽  
Author(s):  
Abdul Jawad ◽  
Amara Ilyas ◽  
Sarfraz Ahmad
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Power Spectra ◽  
Spectral Indices ◽  
Tensor Power ◽  
Planck Data ◽  
Warm Inflation ◽  
Slow Roll ◽  
Scalar Spectral Index ◽  
Inflationary Parameters

We discuss the warm inflation in the presence of shaft potential [Formula: see text], tachyon scalar field and the generalized form of dissipative coefficient [Formula: see text]. In this respect, we investigate the inflationary parameters (slow-roll parameters, number of e-folds, scalar-tensor power spectra, spectral indices, tensor-to-scalar ratio and running of scalar spectral index) in both strong and weak dissipative regimes. It is interesting to mention that our inflationary parametric results (tensor-scalar ratio, spectral index and running of spectral) are consistent with the recent observational data such as BICEP[Formula: see text], WMAP[Formula: see text] and latest Planck data.

scholarly journals Nonminimal coupling inflation with constant slow roll

2021 ◽  
pp. 2150070
Author(s):  
Mehdi Shokri ◽  
Jafar Sadeghi ◽  
Mohammad Reza Setare ◽  
Salvatore Capozziello
Keyword(s):  
Scalar Field ◽  
Equations Of Motion ◽  
Nonminimal Coupling ◽  
Coupling Term ◽  
Microwave Background ◽  
First Order ◽  
Slow Roll ◽  
Wide Range ◽  
Single Field ◽  
Inflationary Parameters

In this paper, we study a single-field inflationary model modified by a nonminimal coupling term between the Ricci scalar [Formula: see text] and the scalar field [Formula: see text] in the context of constant-roll inflation. The first-order formalism is used to analyze the constant-roll inflation instead of the standard methods used in the literature. In principle, the formalism considers two functions of the scalar field, [Formula: see text] and [Formula: see text], which lead to the reduction of the equations of motion to first-order differential equations. The approach can be applied to a wide range of cosmological situations since it directly relates the function [Formula: see text] with Hubbles parameter [Formula: see text]. We perform the inflationary analysis for power-law and exponential couplings, separately. Then, we investigate the features of constant-roll potentials as inflationary potentials. Finally, we compare the inflationary parameters of the models with the observations of Cosmic Microwave Background (CMB) anisotropies in view of realizing a physically motivated model.

scholarly journals Generalization of cosmological attractor approach to Einstein–Gauss–Bonnet gravity

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Ekaterina O. Pozdeeva
Keyword(s):  
Scalar Field ◽  
Spectral Index ◽  
Leading Order ◽  
Bonnet Gravity ◽  
Inflationary Scenario ◽  
Slow Roll ◽  
Inflationary Parameters ◽  
Bonnet Term ◽  
Scalar Perturbations ◽  
Good Agreement

Abstract We construct models with the Gauss–Bonnet term multiplied by a function of the scalar field leading to an inflationary scenario. The consideration is related to the slow-roll approximation. The cosmological attractor approach gives the spectral index of scalar perturbations which is in a good agreement with modern observation and allows for variability of the tensor-to-scalar ratio. We reconstruct models with variability of parameters, which allows one to reproduce cosmological attractor predictions for inflationary parameters in an approximation of the leading order of 1/N in Einstein–Gauss–Bonnet gravity.

scholarly journals Quantum corrections to slow-roll inflation: scalar and tensor modes

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Jens O. Andersen ◽  
Magdalena Eriksson ◽  
Anders Tranberg
Keyword(s):  
Scalar Field ◽  
Quantum Corrections ◽  
Tree Level ◽  
Field Equations ◽  
Slow Roll ◽  
Scalar Field Equations ◽  
Slow Rolling ◽  
Different Sources ◽  
Suitable Potential ◽  
Quadratic Order

Abstract Inflation is often described through the dynamics of a scalar field, slow-rolling in a suitable potential. Ultimately, this inflaton must be identified with the expectation value of a quantum field, evolving in a quantum effective potential. The shape of this potential is determined by the underlying tree-level potential, dressed by quantum corrections from the scalar field itself and the metric perturbations. Following [1], we compute the effective scalar field equations and the corrected Friedmann equations to quadratic order in both scalar field, scalar metric and tensor perturbations. We identify the quantum corrections from different sources at leading order in slow-roll, and estimate their magnitude in benchmark models of inflation. We comment on the implications of non-minimal coupling to gravity in this context.

scholarly journals Conformal mapping of the Misner–Sharp mass from gravitational collapse

2016 ◽  
Vol 25 (07) ◽  
pp. 1650081 ◽  
Author(s):  
Fayçal Hammad
Keyword(s):  
Conformal Mapping ◽  
Gravitational Collapse ◽  
Conformal Transformation ◽  
Conformal Mappings ◽  
Conformal Transformations ◽  
Theories Of Gravity ◽  
Definition Of ◽  
Geometric Definition

The conformal transformation of the Misner–Sharp mass is reexamined. It has recently been found that this mass does not transform like usual masses do under conformal mappings of spacetime. We show that when it comes to conformal transformations, the widely used geometric definition of the Misner–Sharp mass is fundamentally different from the original conception of the latter. Indeed, when working within the full hydrodynamic setup that gave rise to that mass, i.e. the physics of gravitational collapse, the familiar conformal transformation of a usual mass is recovered. The case of scalar–tensor theories of gravity is also examined.

Scalar field fluctuations in the early universe

1988 ◽  
Vol 303 (4) ◽  
pp. 713-727 ◽  
Author(s):  
K. Enqvist ◽  
K.W. Ng ◽  
K.A. Olive
Keyword(s):  
Scalar Field ◽  
Early Universe ◽  
Field Fluctuations

scholarly journals NATURAL SLOW-ROLL INFLATION

1996 ◽  
Vol 11 (08) ◽  
pp. 631-646 ◽  
Author(s):  
R.F. LANGBEIN ◽  
K. LANGFELD ◽  
H. REINHARDT ◽  
L. von SMEKAL
Keyword(s):  
Phase Change ◽  
Early Universe ◽  
Slow Roll ◽  
Slow Roll Inflation

It is shown that the nonperturbative dynamics of a phase change to the nontrivial phase of λφ4-theory in the early universe can give rise to slow-rollover inflation without recourse to unnaturally small couplings.

Sign in / Sign up

Export Citation Format

Share Document