Dynamical system analysis of dark energy models in scalar coupled Metric-Torsion theories

Bhatia, Arshdeep Singh; Sur, Sourav

doi:10.1142/s0218271817501498

Cited by 28 publications

(21 citation statements)

References 62 publications

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“…On the other hand, Ω (m) by definition has no fallacy whatsoever. Therefore, from the practical point of view as well as for transparency in realizing the results physically, it is imperative to stick to the definition of Ω (m) as the matter density parameter, and hence to ρ as the critical density of the universe, while studying cosmology even for the theoretical formulations in the Jordan frame (see [250] for further elaboration).…”

Section: Cosmological Equations and Solutionmentioning

confidence: 99%

Weakly dynamic dark energy via metric-scalar couplings with torsion

Sur¹,

Bhatia

2017

J. Cosmol. Astropart. Phys.

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Abstract. We study the dynamical aspects of dark energy in the context of a non-minimally coupled scalar field with curvature and torsion. Whereas the scalar field acts as the source of the trace mode of torsion, a suitable constraint on the torsion pseudo-trace provides a mass term for the scalar field in the effective action. In the equivalent scalar-tensor framework, we find explicit cosmological solutions representing dark energy in both Einstein and Jordan frames. We demand the dynamical evolution of the dark energy to be weak enough, so that the present-day values of the cosmological parameters could be estimated keeping them within the confidence limits set for the standard ΛCDM model from recent observations. For such estimates, we examine the variations of the effective matter density and the dark energy equation of state parameters over different redshift ranges. In spite of being weakly dynamic, the dark energy component differs significantly from the cosmological constant, both in characteristics and features, for e.g. it interacts with the cosmological (dust) fluid in the Einstein frame, and crosses the phantom barrier in the Jordan frame. We also obtain the upper bounds on the torsion mode parameters and the lower bound on the effective BransDicke parameter. The latter turns out to be fairly large, and in agreement with the local gravity constraints, which therefore come in support of our analysis.

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Section: Cosmological Equations and Solutionmentioning

confidence: 99%

Weakly dynamic dark energy via metric-scalar couplings with torsion

Sur¹,

Bhatia

2017

J. Cosmol. Astropart. Phys.

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“…W = W = 2Λ, due to the only existent torsion mode T μ (in absence of the Holst term) therein. While the coupling β(φ) ∼ φ 2 has had its motivation from the point of view of its natural appearance in metric-torsion theories involving scalar field(s) [97,[148][149][150], the effect of the typical functional form it ascribes to the fractional modification Y (φ) of the constant potential W = 2Λ (of Paper 1) has turned out to be quite fascinating in the cosmological context. Specifically, such a φ 2 -coupling implies an inverse functional dependence of Y on φ, or equivalently, on the cosmic time t in the FRW framework.…”

Section: Discussionmentioning

confidence: 99%

Mimetic-metric-torsion with induced axial mode and phantom barrier crossing

2021

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We extend the basic formalism of mimetic-metric-torsion gravity theory, in a way that the mimetic scalar field can manifest itself geometrically as the source of not just the trace mode of torsion, but its axial (or, pseudo-trace) mode as well. Specifically, we consider the mimetic field to be (i) coupled explicitly to the well-known Holst extension of the Riemann–Cartan action, and (ii) identified with the square of the associated Barbero–Immirzi field, presumably a pseudo-scalar. The conformal symmetry originally prevaling in the theory would still hold, as the associated Cartan transformations do not affect the torsion pseudo-trace, and hence the Holst term. Demanding the theory to preserve the spatial parity symmetry as well, we show a geometric unification of the cosmological dark sector, and the feasibility of a super-accelerating regime in the course of evolution of the universe. From the observational perspective, assuming the cosmological evolution profile to be very close to that for $$\varLambda $$ Λ CDM, we further illustrate a smooth crossing of the so-called phantom barrier at a low red-shift, albeit with a restricted parametric domain. Subsequently, we determine the extent of the super-acceleration by examining the evolution of the relevant torsion parameters.

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“…Such a φ 2 coupling has actually been the trademark of metric-scalar-torsion theories in the literature [107,[167][168][169]. However, in our MMT formalism we crucially have the mimetic constraint (3.31), that takes care of the dynamics of φ, and hence of the mode T µ , thus leaving us with a constant effective potential W .…”

Section: λCdm Evolution From a Specific Form Of Mmt Couplingmentioning

confidence: 99%

“…g µν = −κ 2 g αβ ∂ α φ∂ β φ g µν , where κ denotes the Planck length scale, and the scalar 'mimetic field' φ is assumed dimensionless [21]. 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].…”

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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Dynamical system analysis of dark energy models in scalar coupled Metric-Torsion theories

Cited by 28 publications

References 62 publications

Weakly dynamic dark energy via metric-scalar couplings with torsion

Weakly dynamic dark energy via metric-scalar couplings with torsion

Mimetic-metric-torsion with induced axial mode and phantom barrier crossing

Cosmological dark sector from a mimetic–metric–torsion perspective

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