General scalar–tensor cosmology: analytical solutions via noether symmetry

Massaeli, Erfan; Motaharfar, Meysam; Sepangi, H. R.

doi:10.1140/epjc/s10052-017-4682-3

Cited by 8 publications

(8 citation statements)

References 102 publications

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“…Such probes include weak lensing [21][22][23][24][25][26] and redshift space distortion observations [16,[27][28][29][30][31]. A simple way to account for this tension is to allow [27] for the possibility of extensions of GR in the form of modified theories of gravity [32][33][34][35][36][37][38][39][40][41][42][43][44]. RSD measurements in galaxy redshift surveys [46][47][48][49][50] measure the peculiar velocities of matter and thus infer [51] the growth rate of cosmological perturbations on a range of redshifts and scales.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the fσ8 tension with the Planck15/ΛCDM determination and implications for modified gravity theories

2018

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We construct an updated extended compilation of distinct (but possibly correlated) f σ8(z) redshift space distortion (RSD) data published between 2006 and 2018. It consists of 63 data points and is significantly larger than previously used similar data sets. After fiducial model correction we obtain the best fit Ω0m − σ8 ΛCDM parameters and show that they are at a 5σ tension with the corresponding Planck15/ΛCDM values. Introducing a nontrivial covariance matrix correlating randomly 20% of the RSD data points has no significant effect on the above tension level. We show that the tension disappears (becomes less than 1σ) when a subsample of the 20 most recently published data is used. A partial cause for this reduced tension is the fact that more recent data tend to probe higher redshifts (with higher errorbars) where there is degeneracy among different models due to matter domination. Allowing for a nontrivial evolution of the effective Newton's constant(ga is a parameter) and fixing a Planck15/ΛCDM background we find ga = −0.91 ± 0.17 from the full f σ8 data set while the 20 earliest and 20 latest data points imply ga = −1.28 +0.28 −0.26 and ga = −0.43 +0.46 −0.41 respectively. Thus, the more recent f σ8 data appear to favor GR in contrast to earlier data. Finally, we show that the parametrization f σ8(z) = λσ8Ω(z) γ /(1 + z) β provides an excellent fit to the solution of the growth equation for both GR (ga = 0) and modified gravity (ga = 0).

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Section: Introductionmentioning

confidence: 99%

Evolution of the fσ8 tension with the Planck15/ΛCDM determination and implications for modified gravity theories

2018

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“…was provided. Likewise, Massaeli et al [90] found exact solutions by taking ceratin assumptions in Horndeski theory and explored the possible constraints on free parameters using effective EoS parameter only which turned out as a constant quantity in each case. In [72], Capozziello et.…”

Section: Discussionmentioning

confidence: 99%

Isotropic exact solutions in $$F(R,Y,\phi )$$ gravity via Noether symmetries

2021

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The present article investigates the existence of Noether and Noether gauge symmetries of flat Friedman–Robertson–Walker universe model with perfect fluid matter ingredients in a generalized scalar field formulation namely $$f(R,Y,\phi )$$ f ( R , Y , ϕ ) gravity, where R is the Ricci scalar and Y denotes the curvature invariant term defined by $$Y=R_{\alpha \beta }R^{\alpha \beta }$$ Y = R α β R α β , while $$\phi $$ ϕ represents scalar field. For this purpose, we assume different general cases of generic $$f(R,Y,\phi )$$ f ( R , Y , ϕ ) function and explore its possible forms along with field potential $$V(\phi )$$ V ( ϕ ) by taking constant and variable coupling function of scalar field $$\omega (\phi )$$ ω ( ϕ ) . In each case, we find non-trivial symmetry generator and its related first integrals of motion (conserved quantities). It is seen that due to complexity of the resulting system of Lagrange dynamical equations, it is difficult to find exact cosmological solutions except for few simple cases. It is found that in each case, the existence of Noether symmetries leads to power law form of scalar field potential and different new types of generic function. For the acquired exact solutions, we discuss the cosmology generated by these solutions graphically and discuss their physical significance which favors the accelerated expanding eras of cosmic evolution.

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“…where the left-hand equation is for the cosh-like potential, while the right-hand one is for the sinh-like potential. Since at the GR-de Sitter point: x = ξ = 0, then, from the above equations it follows that this critical point exists for the cosh and sinh-like potentials only if kµ = 1, in which case the mentioned potentials (183) asymptotically approach to the exponential as ϕ → ∞:…”

Section: (Non)emergence Of the λCdm Phase From The Brans-dicke Cosmologymentioning

confidence: 99%

“…Scalar-tensor theories of gravity 41,64,65,[175][176][177][178][179][180][181][182][183][184][185][186][187] are a generalization of the Brans-Dicke theory to allow the BD coupling to be a function of the scalar field: ω BD → ω(φ), i. e., to be a varying parameter:…”

Section: Scalar-tensor Theoriesmentioning

confidence: 99%

Selected topics in scalar–tensor theories and beyond

Quirós

2019

Int. J. Mod. Phys. D

108

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Scalar fields have played an important role in the development of the fundamental theories of physics as well as in other branches of physics such as gravitation and cosmology. For a long time these escaped detection until 2012 year when the Higgs boson was observed for the first time. Since then alternatives to the general theory of relativity like the Brans-Dicke theory, scalar-tensor theories of gravity and their higher derivative generalizations -collectively known as Horndeski theories -have acquired renewed interest. In the present review we discuss on several selected topics regarding these theories, mainly from the theoretical perspective but with due mention of the observational aspect. Among the topics covered in this review we pay special attention to the following: 1) the asymptotic dynamics of cosmological models based in the Brans-Dicke, scalar-tensor and Horndeski theories, 2) inflationary models, extended quintessence and the Galileons, with emphasis in causality and stability issues, 3) the chameleon and Vainshtein screening mechanisms that may allow the elusive scalar field to evade the tight observational constraints implied by the solar system experiments, 4) the conformal frames conundrum with a brief discussion on the disformal transformations and 5) the role of Weyl symmetry and scale invariance in the gravitation theories. The review is aimed at specialists as well as at non-specialists in the subject, including postgraduate students.

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General scalar–tensor cosmology: analytical solutions via noether symmetry

Cited by 8 publications

References 102 publications

Evolution of the fσ8 tension with the Planck15/ΛCDM determination and implications for modified gravity theories

Evolution of the fσ8 tension with the Planck15/ΛCDM determination and implications for modified gravity theories

Isotropic exact solutions in $$F(R,Y,\phi )$$ gravity via Noether symmetries

Selected topics in scalar–tensor theories and beyond

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