Inflationary f (R) Cosmologies

Sami, Heba; Ntahompagaze, Joseph; Abebe, Amare

doi:10.3390/universe3040073

Cited by 11 publications

(4 citation statements)

References 28 publications

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“…Among the modifications of the Einstein-Hilbert action originating from the inclusion of higher curvature terms, a few are of considerable interest. In particular, f (R) theories of gravity has drawn significant interest in the past few years due to its ability to explain the late time cosmic acceleration [21][22][23][24][25][26][27][28][29][30][31][32][33] and its close correspondence with scalar-tensor theories of gravity [34][35][36][37][38][39][40][41]. In addition Lovelock theories of gravity [42][43][44][45][46][47][48][49], f (T ) gravity [50][51][52][53][54][55], higher dimensional along with higher curvature modifications to gravitational dynamics [56][57][58][59][60][61] play crucial roles in explaining various scenarios among the alternative gravity theories.…”

Section: Introductionmentioning

confidence: 99%

Horndeski theories confront the Gravity Probe B experiment

Mukherjee

Chakraborty

2018

Phys. Rev. D

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In this work we have investigated various properties of a spinning gyroscope in the context of Horndeski theories. In particular, we have focused on two specific situations -(a) when the gyroscope follows a geodesic trajectory and (b) when it is endowed with an acceleration. In both these cases, besides developing the basic formalism, we have also applied the same to understand the motion of a spinning gyroscope in various static and spherically symmetric spacetimes pertaining to Horndeski theories. Starting with the Schwarzschild de-Sitter spacetime as a warm up exercise, we have presented our results for two charged Galileon black holes as well as for a black hole in scalar coupled Einstein-Gauss-Bonnet gravity. In all these cases we have shown that the spinning gyroscope can be used to distinguish black holes from naked singularities. Moreover, using the numerical estimation of the geodetic precession from the Gravity Probe B experiment, we have constrained the gauge/scalar charge of the black holes in these Horndeski theories. Implications are also discussed. * sm13ip029@iiserkol.ac.in

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Section: Introductionmentioning

confidence: 99%

Horndeski theories confront the Gravity Probe B experiment

Mukherjee

Chakraborty

2018

Phys. Rev. D

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“…Scalar-tensor theories have been widely explored [1,2,3,4] and their relationship with f (R) gravity theories are discussed [5,6,7]. Recent focus [8,9,10,11,12,13] has been on the f (R) theories as a special class of Brans-Dicke scalar-tensor theories. In the current work we continue to explore this relationship following on our recent work [11].…”

Section: Introductionmentioning

confidence: 99%

A study of perturbations in scalar–tensor theory using 1 + 3 covariant approach

Ntahompagaze

Abebe

Mbonye

2018

Int. J. Mod. Phys. D

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This work discusses scalar-tensor theories of gravity, with a focus on the Brans-Dicke subclass, and one that also takes note of the latter's equivalence with f (R) gravitation theories. A 1+3 covariant formalism is used in this case to discuss covariant perturbations on a background Friedmann-Laimaître-Robertson-Walker (FLRW) space-time. Linear perturbation equations are developed, based on gauge-invariant gradient variables. Both scalar and harmonic decompositions are applied to obtain second-order equations. These equations can then be used for further analysis of the behavior of the perturbation quantities in such a scalar-tensor theory of gravitation. Energy density perturbations are studied for two systems, namely for a scalar fluid-radiation system and for a scalar fluid-dust system, for R n models. For the matterdominated era, it is shown that the dust energy density perturbations grow exponentially, a result which agrees with those already in existing literature. In the radiation-dominated era, it is found that the behavior of the radiation energy-density perturbations is oscillatory, with growing amplitudes for n > 1, and with decaying amplitudes for 0 < n < 1. This is a new result.keywords : f (R) gravity -scalar-tensor -scalar field -cosmology -covariant perturbation. P ACSnumbers : 04.50. Kd, 95.36.+x, 98.80.Cq; M SCnumbers : 83Dxx, 83Fxx, 83Cxx arXiv:1801.01758v1 [gr-qc] 5 Jan 2018to study linear perturbation in General Relativity [15]. The same studies has been done in f (R) gravity at linear order and results have been obtained [17,18]. In scalar-tensor theory, the 1 + 3 covariant linear perturbation has been studied [19,20], but it was limited to vacuum case.The assumption that the hyper-surfaces are with constant scalar field was made in that study. Those hyper-surfaces are perpendicular to a vector field.In this paper, we consider hyper-surfaces with constant curvature. They have been considered for f (R) covariant perturbations [18,17,21]. This consideration is taken due to the equivalence between metric f (R) theory of gravity and Brans-Dicke scalar-tensor theory. The equivalence between f (R) gravity and scalar-tensor theory in five dimensions have been considered in [7,22], where Jordan frame was given much attention and bulk consideration which resulted in hyper-surfaces of four dimensional space-times. In our study, the hyper-surfaces are constructed from 1 + 3 covariant decomposition of spacetime such that they have three dimensions. The work presented in this paper is a follow-up of the work previously done by the authors [11], where the equivalence between f (R) theory and scalar-tensor theory has been explored. Here, this equivalence is extended to covariant linear perturbations for two fluid system with the consideration that scalar field behaves like a fluid (scalar fluid). The two fluid system (radiation-scalar field or dust-scalar field) are considered with the motivation that towards the end of a scalar field driven inflation the universe experienced a mixture of scalar field ...

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“…In the bottom-up approach of doing cosmology one first specifies a cosmology (a(t)) and, given a matter content, tries to find out what functional form of f (R) gravity can produces the specified dynamics. This can be achieved via various reconstruction methods [21,22,23,24,25,26,27]. Then one can carry out a dynamical systems analysis of the reconstructed f (R) model.…”

Section: The Form-independent Dynamical System Approachmentioning

confidence: 99%

A note on the dynamical system formulations in $f(R)$ gravity

Chakraborty,

Dunsby,

Macdevette

2021

Preprint

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A number of dynamical system formulations have been proposed over the last few years to analyse cosmological solutions in f (R) gravity. The aim of this article is to provide a brief introduction to the different approaches, presenting them in a chronological order as they appeared in the history of the relevant scientific literature. In this way we illuminate how the shortcoming(s) of an existing formulation encouraged the development of an alternative formulation. Whenever possible, a 2-dimensional phase portrait is given for a better visual representation of the dynamics of phase space. We also touch upon how cosmological perturbations can be analyzed using the phase space language.

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Inflationary f (R) Cosmologies

Cited by 11 publications

References 28 publications

Horndeski theories confront the Gravity Probe B experiment

Horndeski theories confront the Gravity Probe B experiment

A study of perturbations in scalar–tensor theory using 1 + 3 covariant approach

A note on the dynamical system formulations in $f(R)$ gravity

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