Cosmology in Poincaré gauge gravity with a pseudoscalar torsion

Lu, Jianbo; Chee, Guoying

doi:10.1007/jhep05(2016)024

Cited by 25 publications

(22 citation statements)

References 104 publications

(183 reference statements)

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“…In this case, the exponential growth of perturbation makes it large (and non-linear) in the Hubble time. The analysis given in this Section shows that the self-accelerating solution (23), under assumption (53), is unstable because of the exponentially growing mode (52).…”

Section: Limit Of Small λmentioning

confidence: 99%

“…To study the linear perturbations about the self-accelerating background (23), it is convenient to make the 3-dimensional Fourier decomposition. We use the same notation for the Fouriertransformed variables and replace spatial derivatives ∂ã ≡ e μ a ∂ µ with ikã, where k is the 3-dimensional momentum.…”

Section: Perturbations About Self-accelerating Solution: 3+1 Decomposmentioning

confidence: 99%

“…This does not rule out the possibility of stable self-acceleration with torsion of the order of the effective cosmological constant.Self-accelerating solutions, without explicit cosmological constant term in the action, were found in various gravities with dynamical torsion in Refs. [15][16][17][18][19][20][21][22][23][24]. The open question is the stability of self-accelerating solutions in these theories, at least at the linearized level.…”

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confidence: 99%

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The stability of self-accelerating Universe in modified gravity with dynamical torsion

Nikiforova

2017

Int. J. Mod. Phys. A

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We consider the model of modified gravity with dynamical torsion. This model was previously found to have promising stability properties about various backgrounds. Here we study the stability of linear perturbations about the self-accelerating solution. We apply the (3 + 1)-decomposition and consider the scalar sector of perturbations. We find that the number of degrees of freedom is equal to 2, which is the same as in Minkowski background. However, there is at least one instability in the scalar sector, if the value of background torsion is large enough. This does not rule out the possibility of stable self-acceleration with torsion of the order of the effective cosmological constant.

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Section: Limit Of Small λmentioning

confidence: 99%

Section: Perturbations About Self-accelerating Solution: 3+1 Decomposmentioning

confidence: 99%

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confidence: 99%

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The stability of self-accelerating Universe in modified gravity with dynamical torsion

Nikiforova

2017

Int. J. Mod. Phys. A

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“…Lots of exciting astrophysical observations and corresponding theoretical findings have motivated people to carry out research on alternative theories of general relativity. Several theories of modified gravity have been proposed for such explorations [1][2][3][4][5][6]. Among them, the f(R) theory and the Brans-Dicke (BD) theory are highly noteworthy [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Determination of time evolution of the gravitational constant in the framework of Brans-Dicke Theory: An easy wa

Roy¹

2021

World J. Adv. Res. Rev.

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The present article demonstrates a very simple mathematical way to determine the time-dependence of the dynamical gravitational constant () in the framework of the Brans-Dicke theory of gravity. Brans-Dicke field equations, for a matter-dominated, pressure-less and spatially flat universe with homogeneous and isotropic space-time, have been used for this formulation. The gravitational constant () is the reciprocal of the Brans-Dicke scalar field (). Using a simple ansatz, which represents the Brans-Dicke scalar field () as a function of time, the possible values of a constant parameter (constituting the ansatz) have been calculated with the help of the field equations, using the values of some cosmological parameters at the present time. The values of that parameter (belonging to the ansatz) lead to the conclusion that the scalar field () decreases and consequently the gravitational constant () increases with time. The value of the relative time-rate of change of the gravitational constant (i.e., ) has also been estimated and this quantity has been found to be independent of time. Time-dependence of and has been depicted graphically for all values of the parameter belonging to the ansatz. The novel features of this study are that the gravitational field equations did not have to be solved, unlike other studies, to arrive at the results and the mathematical scheme for calculations is extremely easy in comparison to other recent studies in this regard.

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“…Such a parametrization not only ensures the invariance of g µν under a conformal demonstrates Cartan gauge invariance [157], the square-torsion theory [158][159][160][161], the degenerate tetrad formalism [162][163][164][165][166], the non-minimal metric-scalar-torsion coupling formalism [167][168][169], and so on. Moreover, a lot of attention has been drawn in recent years by modified versions of the (curvature-free) teleparallel gravity theories [170][171][172][173][174][175][176][177][178][179][180][181][182][183][184][185], apart from the modern refinements of Poincaré gauge theory of gravity [186][187][188][189][190][191][192][193][194][195][196]. Now, given such a wide applicability of torsion, it seems really interesting to look for a generalized mimetic gravity formulation in presence of torsion, especially from the point of view of getting an observational support for the latter, amidst its miniscule experimental evidence till date [197][198]…”

Section: Introductionmentioning

confidence: 99%

Cosmological dark sector from a mimetic–metric–torsion perspective

Chothe

Dutta

Sur

2019

Int. J. Mod. Phys. D

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We generalize the basic theory of mimetic gravity by extending its purview to the general metriccompatible geometries that admit torsion, in addition to curvature. This essentially implies reinstating the mimetic principle of isolating the conformal degree of freedom of gravity in presence of torsion, by parametrizing both the physical metric and torsion in terms of the scalar 'mimetic' field and the metric and torsion of a fiducial space. We assert the requisite torsion parametrization from an inspection of the fiducial space Cartan transformation which, together with the conformal transformation of the fiducial metric, preserve the physical metric and torsion. In formulating the scalar-tensor equivalent Lagrangian, we consider an explicit contact coupling of the mimetic field with torsion, so that the former can manifest itself geometrically as the source of a torsion mode, and most importantly, give rise to a viable 'dark universe' picture from a mimicry of an evolving dust-like cosmological fluid with a non-zero pressure. A further consideration of higher derivatives of the mimetic field in the Lagrangian leads to physical bounds on the mimetic-torsion coupling strength, which we determine explicitly. * transformation of g µν , but also implicates that φ is left non-dynamical by the condition for the invertibility of g µν , viz. −κ 2 g µν ∂ µ φ∂ ν φ = 1 . This condition could be implemented in the theory as a constraint, using a Lagrange multiplier λ in an equivalent mimetic action. A further equivalence of the latter with the singular Brans-Dicke (BD) action (in which the BD parameter w = − 3 2 ) eventually shows that mimetic gravity is indeed a ratification of GR being raised to the status of a scalar-tensor equivalent MG theory [21][22][23][24]29].Detailed studies have revealed many attractive features of the basic mimetic model of Chemseddine and Mukhanov (henceforth, the CM model [21]) and its various extensions, from the perspectives of both cosmology and astrophysics . In particular, the CM Lagrangian extended by a potential V (φ) leads to the scenarios of a cosmologically evolving fluid -the so-called 'mimetic fluid' -which characterizes dust, albeit with a nonvanishing pressure 1 [22]. As such, no propagating scalar perturbation mode is there to suppress the growth of structures at smaller (sub-galactic) scales [26,27]. Nor it is possible to define the quantum fluctuations to the (non-dynamical) field φ, so that the latter can provide the seeds of the observed large scale structure of the universe [22,23]. A reasonable supposition has therefore been to extend the CM theory further by incorporating higher derivative (HD) term(s) for φ, e.g. (✷φ) 2 , which lead(s) to a non-vanishing sound speed c s of the mimetic matter perturbations, keeping the background solution unaffected qualitatively 2 [22,23,29]. However, the HD terms in general make the theory susceptible to Ostrogradsky ghost or(and) gradient instabilities [26,27,[64][65][66][67], possible wayouts of which point to more complicated extensions...

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Cosmology in Poincaré gauge gravity with a pseudoscalar torsion

Cited by 25 publications

References 104 publications

The stability of self-accelerating Universe in modified gravity with dynamical torsion

The stability of self-accelerating Universe in modified gravity with dynamical torsion

Determination of time evolution of the gravitational constant in the framework of Brans-Dicke Theory: An easy wa

Cosmological dark sector from a mimetic–metric–torsion perspective

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