Testing unimodular gravity

Jain, Pankaj; Karmakar, Purnendu; Mitra, Subhadip; Panda, Sukanta; Singh, Narayani P.

doi:10.1088/1475-7516/2012/05/020

Cited by 34 publications

(72 citation statements)

References 30 publications

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“…Therefore, the obtained action (25) does not include the cosmological constant. This tells that the cosmological constant Λ does not affect the dynamics even in the action (24).…”

Section: Generalization Of Unimodular Gravitymentioning

confidence: 93%

Some solutions for one of the cosmological constant problems

Nojiri

2016

Mod. Phys. Lett. A

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We propose several covariant models which may solve one of the problems in the cosmological constant. One of the model can be regarded as an extension of sequestering model. Other models could be regarded as extensions of the covariant formulation of the unimodular gravity. The contributions to the vacuum energy from the quantum corrections from the matters are absorbed into a redefinition of a scalar field and the quantum corrections become irrelevant to the dynamics. In a class of the extended unimodular gravity models, we also consider models which are regarded as topological field theories. The models can be extended and not only the vacuum energy but any quantum corrections to the gravitational action could become irrelevant for the dynamics. We find, however, that the BRS symmetry in the topological field theories is broken spontaneously and therefore the models might not be consistent.Comment: LaTeX 9 pages, references are added, the version to appear in Mod.Phys.Lett.

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“…Therefore, the obtained action (25) does not include the cosmological constant. This tells that the cosmological constant Λ does not affect the dynamics even in the action (24).…”

Section: Generalization Of Unimodular Gravitymentioning

confidence: 93%

Some solutions for one of the cosmological constant problems

Nojiri

2016

Mod. Phys. Lett. A

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“…For ξ = 6, the action is invariant under the general unimodular coordinate transformations, and A is treated as a scalar field [15,16].…”

Section: Unimodular Theory Of Gravitymentioning

confidence: 99%

“…In Sec. 2, we describe the proposed model of the unimodular theory of gravity [15,16] in brief. In Sec.…”

Section: Introductionmentioning

confidence: 99%

Unimodular theory of gravity and inflation

Cho

Singh

2015

Class. Quantum Grav.

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We investigate inflation and its scalar perturbation driven by a massive scalar field in the unimodular theory of gravity. We introduce a parameter ξ with which the theory is invariant under general unimodular coordinate transformations. When the unimodular parameter is ξ = 6, the classical picture of inflation is reproduced in the unimodular theory because it recovers the background equations of the standard theory of general relativity. We show that for ξ = 6, the theory is equivalent to the standard theory of general relativity at the perturbation level. Unimodular gravity constrains the gauge degree of freedom in the scalar perturbation, but the perturbation equations are similar to those in general relativity. For ξ = 6, we derive the power spectrum and the spectral index, and obtain the unimodular correction to the tensorto-scalar ratio. Depending on the value of ξ, the correction can either raise or lower the value of the tensor-to-scalar ratio. IntroductionThe de Sitter expansion in the period of inflation, provides a solution to the flatness problem, the horizon problem, the entropy problem etc [1][2][3][4][5][6][7][8][9]. The inflationary model also explains the structure formation of the Universe by considering the perturbations which are generated in the period of inflation. Not only for the period of inflation in the early universe, the role of the exponential expansion of the Universe is important in the current era of the accelerating universe [10,11]. There are many theories which describe the current accelerating universe such as DGP model, f (R)-gravity and scalar field models, etc. The scalar field model is one of the simplest model. The cosmological constant is also one of the explanation for the current acceleration of the Universe. However, adding the cosmological constant term, the theory suffers from the fine tuning problem.The unimodular theory of gravity was initially developed in Refs. [12,13]. One of the motivations of considering the unimodular theory of gravity is to solve the cosmological constant problem [14]. Another interesting implication is that it explains the current expansion of the Universe by considering only single component such as the cosmological constant, or by the nonrelativistic matter [15,16]. The full metric is decomposed in the unimodular metric and a scalar field [15,16]. The value of the determinant of the unimodular metric is the same as the determinant of the Minkowski metric. The basic idea of the unimodular theory of gravity is to consider the determinant of metric not as a dynamical variable [14,[17][18][19], and hence the cosmological constant term is absent from the action. However, it was shown in Ref. [14] that the cosmological constant appears as an integration constant in this theory. Some progress in the unimodular theory of gravity has been discussed in Refs. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In the case of the unimodular theory we have the unimodular constraint equation, and hence it reduces the gauge...

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“…In other words, it would be more appropriate to state that unimodular gravity, in a sense, can offer a proposal to solve the cosmological problem. It is important to mention that in the context of unimodular gravity the problem of late-time acceleration of the universe can be developed, where the metric can be decomposed in the unimodular metric part and a scalar field a e-mail: sthoundjo@yahoo.fr part [23][24][25]. Instead of considering GR, different kinds of modified gravity based on the curvature scalar have been performed in the recent years, as f (R) [31][32][33][34][35][36][37][38][39] where R is the curvature scalar, f (R, T ), T being the trace of the energy-momentum tensor [40][41][42][43][44][45][46][47][48][49], and f (G), G denoting the Gauss-Bonnet (GB) invariant .…”

Section: Introductionmentioning

confidence: 99%

Unimodular f(G) gravity

Nassur¹,

Ainamon²,

Houndjo³

et al. 2017

Eur. Phys. J. C

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In this paper we study a modified version of unimodular general relativity in the context of f (G), G denoting the Gauss-Bonnet invariant. We focus on Bianchi-type I and Friendmann-Robertson-Walker universes and search for unimodular f (G) models according to the de Sitter and power-law solutions. Assuming unimodular f (G) gravity as a perfect fluid and making use of the slow-roll parameters, the inflationary model has been reconstructed in concordance with the Planck observational data. Moreover, we investigate the realization of the bounce and loop quantum cosmological ekpyrotic paradigms. Assuming suitable and appropriate scale factors, unimodular f (G) models able to reproduce superbounce and ekpyrotic scenarios have been reconstructed.

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Testing unimodular gravity

Cited by 34 publications

References 30 publications

Some solutions for one of the cosmological constant problems

Some solutions for one of the cosmological constant problems

Unimodular theory of gravity and inflation

Unimodular f(G) gravity

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