On the equation of state of dark energy

Polarski, David; André, Ranquet

doi:10.1016/j.physletb.2005.09.008

Cited by 43 publications

(42 citation statements)

References 30 publications

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“…Equation (17) can be extended for spatially non-flat universes [39] but we restrict ourselves to spatially flat universes. We also define the effective equation of state…”

Section: A Definitions and Equationsmentioning

confidence: 99%

Conditions for the cosmological viability off(R)dark energy models

et al. 2007

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We derive the conditions under which dark energy models whose Lagrangian densities f are written in terms of the Ricci scalar R are cosmologically viable. We show that the cosmological behavior of f (R) models can be understood by a geometrical approach consisting in studying the m(r) curve on the (r, m) plane, where m ≡ Rf,RR/f,R and r ≡ −Rf,R/f with f,R ≡ df /dR. This allows us to classify the f (R) models into four general classes, depending on the existence of a standard matter epoch and on the final accelerated stage. The existence of a viable matter dominated epoch prior to a late-time acceleration requires that the variable m satisfies the conditions m(r) ≈ +0 and dm/dr > −1 at r ≈ −1. For the existence of a viable late-time acceleration we require instead either (i) m = −r − 1 , ( √ 3 − 1)/2 < m ≤ 1 and dm/dr < −1 or (ii) 0 ≤ m ≤ 1 at r = −2. These conditions identify two regions in the (r, m) space, one for the matter era and the other for the acceleration. Only models with a m(r) curve that connects these regions and satisfy the requirements above lead to an acceptable cosmology. The models of the type f (R) = αR −n and f = R + αR −n do not satisfy these conditions for any n > 0 and n < −1 and are thus cosmologically unacceptable. Similar conclusions can be reached for many other examples discussed in the text. In most cases the standard matter era is replaced by a cosmic expansion with scale factor a ∝ t 1/2 . We also find that f (R) models can have a strongly phantom attractor but in this case there is no acceptable matter era.

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“…Equation (17) can be extended for spatially non-flat universes [39] but we restrict ourselves to spatially flat universes. We also define the effective equation of state…”

Section: A Definitions and Equationsmentioning

confidence: 99%

Conditions for the cosmological viability off(R)dark energy models

et al. 2007

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“…Throughout this work we assume spatial flatness though this prior while well motivated theoretically can be challenged [48]. As has been shown in [43], two different types of observations, e.g., determination of the luminosity distance and the inhomogeneity growth factor in the non-relativistic component as functions of redshift, are necessary and sufficient for the total reconstruction of the microscopic Lagrangian (1) of scalar-tensor gravity.…”

Section: Introductionmentioning

confidence: 99%

Scalar–tensor models of normal and phantom dark energy

Gannouji

Polarski

André

et al. 2006

J. Cosmol. Astropart. Phys.

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223

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We consider the viability of dark energy (DE) models in the framework of the scalar-tensor theory of gravity, including the possibility to have a phantom DE at small redshifts z as admitted by supernova luminosity-distance data. For small z, the generic solution for these models is constructed in the form of a power series in z without any approximation. Necessary constraints for DE to be phantom today and to cross the phantom divide line p = −ρ at small z are presented. Considering the Solar System constraints, we find for the postNewtonian parameters that γ P N < 1 and γ P N,0 ≈ 1 for the model to be viable, and β P N,0 > 1 (but very close to 1) if the model has a significantly phantom DE today. However, prospects to establish the phantom behaviour of DE are much better with cosmological data than with Solar System experiments. Earlier obtained results for a Λ-dominated universe with the vanishing scalar field potential are extended to a more general DE equation of state confirming that the cosmological evolution of these models rule them out. Models of currently fantom DE which are viable for small z can be easily constructed with a constant potential; however, they generically become singular at some higher z. With a growing potential, viable models exist up to an arbitrary high redshift.

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“…However, the precision of curvature measurements is only at the percent level at best (e.g., [1,2]), whereas the expected level of curvature in standard inflationary scenarios is generally much smaller. Moreover, obtaining the most precise limits on curvature requires assuming a particular simple form for the dark energy evolution due to the well-known "geometric degeneracy" between curvature and dark energy [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. Inferences about inflation based on such curvature constraints are only valid if the assumed dark energy behavior is an adequate description of the true evolution.…”

Section: Introductionmentioning

confidence: 99%

Testing flatness of the universe with probes of cosmic distances and growth

Mortonson

2009

Phys. Rev. D

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When using distance measurements to probe spatial curvature, the geometric degeneracy between curvature and dark energy in the distance-redshift relation typically requires either making strong assumptions about the dark energy evolution or sacrificing precision in a more model-independent approach. Measurements of the redshift evolution of the linear growth of perturbations can break the geometric degeneracy, providing curvature constraints that are both precise and model-independent. Future supernova, CMB, and cluster data have the potential to measure the curvature with an accuracy of σ(ΩK) = 0.002, without specifying a particular dark energy phenomenology. In combination with distance measurements, the evolution of the growth function at low redshifts provides the strongest curvature constraint if the high-redshift universe is well approximated as being purely matter dominated. However, in the presence of early dark energy or massive neutrinos, the precision in curvature is reduced due to additional degeneracies, and precise normalization of the growth function relative to recombination is important for obtaining accurate constraints. Curvature limits from distances and growth compare favorably to other approaches to curvature estimation proposed in the literature, providing either greater accuracy or greater freedom from dark energy modeling assumptions, and are complementary due to the use of independent data sets. Model-independent estimates of curvature are critical for both testing inflation and obtaining unbiased constraints on dark energy parameters.

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On the equation of state of dark energy

Cited by 43 publications

References 30 publications

Conditions for the cosmological viability off(R)dark energy models

Conditions for the cosmological viability off(R)dark energy models

Scalar–tensor models of normal and phantom dark energy

Testing flatness of the universe with probes of cosmic distances and growth

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