Delicate<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>f</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>R</mml:mi><mml:mo stretchy="false">)</mml:mo></mml:math>gravity models with a disappearing cosmological constant and observational constraints on the model parameters

Dev, Abha; Jain, Deepak; Jhingan, Sanjay; Nojiri, Shin’ichi; Sami, M.; Thongkool, I.

doi:10.1103/physrevd.78.083515

Cited by 87 publications

(63 citation statements)

References 133 publications

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“…If α = 0 and x = h − 3 (this case corresponds to the cases (1)- (6) presented above), we find 28) which is equivalent to Eq. (4.20) with α 1 = α 2 = 0.…”

Section: The Solution Of F (R G) Is Given Bymentioning

confidence: 98%

Finite-time future singularities in modified Gauss–Bonnet and ℱ(R,G) gravity and singularity avoidance

et al. 2010

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We study all four types of finite-time future singularities emerging in late-time accelerating (effective quintessence/phantom) era from F(R, G)-gravity, where R and G are the Ricci scalar and the Gauss-Bonnet invariant, respectively. As an explicit example of F(R, G)-gravity, we also investigate modified Gauss-Bonnet gravity, so-called F (G)-gravity. In particular, we reconstruct the F (G)-gravity and F(R, G)-gravity models where accelerating cosmologies realizing the finite-time future singularities emerge. Furthermore, we discuss a possible way to cure the finite-time future singularities in F (G)-gravity and F(R, G)-gravity by taking into account higher-order curvature corrections. The example of non-singular realistic modified Gauss-Bonnet gravity is presented.It turns out that adding such non-singular modified gravity to singular Dark Energy makes the combined theory to be non-singular one as well.PACS numbers: 04.50. Kd, 95.36.+x, Recent observations have implied that the current expansion of the universe is accelerating [1, 2]. There exist two broad categories to explain this phenomena [3][4][5][6][7][8][9][10][11][12]. One is the introduction of "dark energy" in the framework of general relativity. The other is the investigation of a modified gravitational theory, e.g., f (R)-gravity, in which the action is described by the Ricci scalar R plus an arbitrary function f (R) of R (for reviews, see [6][7][8][9][10] It is clear that singular dark energy may lead to various instabilities in the current universe

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“…If α = 0 and x = h − 3 (this case corresponds to the cases (1)- (6) presented above), we find 28) which is equivalent to Eq. (4.20) with α 1 = α 2 = 0.…”

Section: The Solution Of F (R G) Is Given Bymentioning

confidence: 98%

Finite-time future singularities in modified Gauss–Bonnet and ℱ(R,G) gravity and singularity avoidance

et al. 2010

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“…It is well known that f (R) theories can be considered as equivalent scalar-tensor theories. It is easy to visualise curvature singularity in a f (R) theory by looking at the form of the potential appearing in its equivalent scalar-tensor theory in the Jordan frame [19]. Due to the nonlinear motion of the scalar field, the oscillations around the potential minimum can make the field displaced to the singular point.…”

Section: Introductionmentioning

confidence: 99%

“…It is shown that past singularities may be prevented for a certain range of parameters. These singularities may also occur in future and can be avoided for fine-tuned initial conditions [19,23]. It is also realised that the curvature singularities can be eliminated by adding an extra curvature term to the Lagrangian [22,24].…”

Section: Introductionmentioning

confidence: 99%

Curvature singularity inf(R)theories of gravity

2015

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Although f (R) modification of late time cosmology is successful in explaining present cosmic acceleration, it is difficult to satisfy the fifth-force constraint simultaneously. Even when the fifth-force constraint is satisfied, the effective scalar degree of freedom may move to a point (close to its potential minima) in the field space where the Ricci scalar diverges. We elucidate this point further with a specific example of f (R) gravity that incorporates several viable f (R) gravity models in the literature. In particular, we show that the nonlinear evolution of the scalar field in pressureless contracting dust can easily lead to the curvature singularity, making this theory unviable.

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“…This problem arises due to the dynamics of the effective scalar degree of freedom, χ, in the high curvature regime. Therefore, the problem may be cured by adding higher curvature corrections that modify the structure of the potential around the large R region, as already noted in the original reference [13] and later discussed in [27]. In general, higher curvature corrections may be written as a 2 R 2 + a 3 R 3 + · · · , and so the most natural choice of the leading order term will be R 2 /µ 2 .…”

Section: Adding Higher Curvature Corrections To F (R) Gravitymentioning

confidence: 99%

“…This is done again by constructing relativistic star solutions. A higher curvature correction changes the structure of the effective potential for the scalar degree of freedom around the singularity [13,27]. We consider a modified version of Starobinsky's f (R) [13], adding a correction term proportional to R m (m ≥ 2).…”

Section: Introductionmentioning

confidence: 99%

Can higher curvature corrections cure the singularity problem inf(R)gravity?

Kobayashi

Maeda

2009

Phys. Rev. D

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Although f (R) modified gravity models can be made to satisfy solar system and cosmological constraints, it has been shown that they have the serious drawback of the nonexistence of stars with strong gravitational fields. In this paper, we discuss whether or not higher curvature corrections can remedy the nonexistence consistently. The following problems are shown to arise as the costs one must pay for the f (R) models that allow for neutrons stars: (i) the leading correction must be fine-tuned to have the typical energy scale µ 10 −19 GeV, which essentially comes from the free fall time of a relativistic star; (ii) the leading correction must be further fine-tuned so that it is not given by the quadratic curvature term. The second problem is caused because there appears an intermediate curvature scale, and laboratory experiments of gravity will be under the influence of higher curvature corrections. Our analysis thus implies that it is a challenge to construct viable f (R) models without very careful and unnatural fine-tuning.

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Delicatef(R)gravity models with a disappearing cosmological constant and observational constraints on the model parameters

Cited by 87 publications

References 133 publications

Finite-time future singularities in modified Gauss–Bonnet and ℱ(R,G) gravity and singularity avoidance

Finite-time future singularities in modified Gauss–Bonnet and ℱ(R,G) gravity and singularity avoidance

Curvature singularity inf(R)theories of gravity

Can higher curvature corrections cure the singularity problem inf(R)gravity?

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