Perturbations of the Robertson-Walker space - Multicomponent sources and generalized gravity

Hwang, Jai‐chan

doi:10.1086/170206

Cited by 165 publications

(339 citation statements)

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“…Note the presence of the Ricci curvature scalar R in the left-hand side, as well as its perturbation δR in the right-hand side: the latter term is not trivial, since it contains δφ; from [27] we see that in the synchronous gauge it is in fact…”

Section: B Perturbationsmentioning

confidence: 95%

Tracking extended quintessence

2000

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We investigate the cosmological role of a Tracking Field φ in Extended Quintessence scenarios, where the dynamical vacuum energy driving the acceleration of the universe today possesses an explicit coupling with the Ricci scalar, R, of the form F (φ)R/2, where F (φ) mimics General Relativity today, F (φ0) = 1/8πG. We analyse explicit non-minimally coupled (NMC) models where F (φ) = 1/8πG + ξ(φ 2 − φ 2 0 ), with ξ is the coupling constant and φ0 is the Q value today. Tracker solutions for these NMC models, with inverse power-law potentials, possess an initial enhancement of the scalar field dynamics, named R-boost, caused by the effective potential generated by the Ricci scalar in the Klein-Gordon equation. During this phase the field performs a "gravitational" slow rolling until the true potential becomes important. We give accurate analytic formulas describing the R-boost, showing that the Quintessence energy in this phase scales with the redshift z as (1 + z) 2 . When the R-boost ends, the field trajectory matches the tracker solution in minimally coupled theories. We compute perturbations in these Tracking Extended Quintessence models, by integrating the full set of equations for the evolution of linear fluctuations in scalar-tensor theories of gravity, and assuming Gaussian scale-invariant initial perturbations. The Integrated Sachs Wolfe (ISW) effect on the Cosmic Microwave Background (CMB) angular spectrum causes a change δC /C 2[1 − 8πGF (φ dec )] at < ∼ 10, where dec stands for decoupling. Similarly, the CMB acoustic peaks multipoles shift compared to ordinary tracking Quintessence models by roughly an amount δ / [8πGF (φ dec ) − 1]/8. The turnover wavenumber kturn in the matter power spectrum shifts by an amount δkturn/kturn [1 − 8πGF (φeq)]/2, where eq stands for matter-radiation equivalence. All these corrections may assume positive as well as negative values, depending on the sign of the NMC parameter ξ. We show that the above effects can be as large as 10 − 30% with respect to equivalent cosmological constant and ordinary tracking Quintessence models, respecting all the existing experimental constraints on scalartensor theories of gravity. These results demonstrate that the playground where the next decade data will have their impact includes the nature of the dark energy in the Universe, as well as the structure of the theory of gravity.

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Section: B Perturbationsmentioning

confidence: 95%

Tracking extended quintessence

2000

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“…We present a complete set of equations describing the scalar-type perturbation without fixing the temporal gauge condition, i.e., in a gauge-ready form [8,1,2]:…”

Section: Perturbed World Model and Basic Equationsmentioning

confidence: 99%

“…In the following we briefly summarize the gauge-ready strategy suggested by Bardeen [8] and elaborated in [1]; see [2] for a recent extension. Under the gauge transformationx a = x a + ξ a with ξ t ≡ aξ 0 (0 = η) the perturbed metric and fluid quantities change as [1,2]:…”

Section: Perturbed World Model and Basic Equationsmentioning

confidence: 99%

Cosmological perturbations with multiple fluids and fields

Hwang

Noh

2002

Class. Quantum Grav.

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107

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We consider the evolution of perturbed cosmological spacetime with multiple fluids and fields in Einstein gravity. Equations are presented in gauge-ready forms, and are presented in various forms using the curvature (Φ or ϕχ) and isocurvature (S (ij) or δφ (ij) ) perturbation variables in the general background with K and Λ. We clarify the conditions for conserved curvature and isocurvature perturbations in the large-scale limit. Evolutions of curvature perturbations in many different gauge conditions are analysed extensively. In the multi-field system we present a general solution to the linear order in slow-roll parameters.

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“…(13). Hence, we can investigate the gauge transformation properties of such a combination in a frame independent way [19]. For later convenience, we split eqs.…”

Section: Perturbed Field Equationsmentioning

confidence: 99%

Evolution of cosmological perturbations in nonsingular string cosmologies

2001

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In a class of non-singular cosmologies derived from higher-order corrections to the low-energy bosonic string action, we derive evolution equations for the most general cosmological scalar, vector and tensor perturbations. In the large scale limit, the evolutions of both scalar and tensor perturbations are characterised by conserved quantities, the usual curvature perturbation in the uniform-field gauge and the tensor-type perturbed metric. The vector perturbation is not affected, being described by the conservation of the angular momentum of the fluid component in the absence of any additional dissipative process. For the scalar-and tensor-type perturbations, we show how, given a background evolution during kinetic driven inflation of the dilaton field, we can obtain the final power spectra generated from the vacuum quantum fluctuations of the metric and the dilaton field during the inflation.PACS numbers: 98.80.Hw

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Perturbations of the Robertson-Walker space - Multicomponent sources and generalized gravity

Cited by 165 publications

References 0 publications

Tracking extended quintessence

Tracking extended quintessence

Cosmological perturbations with multiple fluids and fields

Evolution of cosmological perturbations in nonsingular string cosmologies

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