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On the growth of linear perturbations
Auteur(s): Polarski D., Gannouji Radouane
(Article) Publié:
Modern Physics Letters B, vol. 660 p.439-443 (2007)
Texte intégral en Openaccess :
Ref HAL: in2p3-00179750_v1
Ref Arxiv: 0710.1510
DOI: 10.1016/j.physletb.2008.01.032
WoS: 000254034000001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
138 Citations
Résumé: We consider the linear growth of matter perturbations in various dark energy (DE) models. We show the existence of a constraint valid at $z=0$ between the background and dark energy parameters and the matter perturbations growth parameters. For $\Lambda$CDM $\gamma'_0\equiv \frac{d\gamma}{dz}_0$ lies in a very narrow interval $-0.0195 \le \gamma'_0 \le -0.0157$ for $0.2 \le \Omega_{m,0}\le 0.35$. Models with a constant equation of state inside General Relativity (GR) are characterized by a quasi-constant $\gamma'_0$, for $\Omega_{m,0}=0.3$ for example we have $\gamma'_0\approx -0.02$ while $\gamma_0$ can have a nonnegligible variation. A smoothly varying equation of state inside GR does not produce either $|\gamma'_0|>0.02$. A measurement of $\gamma(z)$ on small redshifts could help discriminate between various DE models even if their $\gamma_0$ is close, a possibility interesting for DE models outside GR for which a significant $\gamma'_0$ can be obtained.
Commentaires: 8 pages, 8 figures
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Scalar-Tensor Dark Energy Models
Auteur(s): Gannouji Radouane, Polarski D., Ranquet Andre, Starobinsky A.A.
Conference: 11th Marcel Grossmann Meeting on General Relativity (MG 11) (Berlin, DE, 2007)
Actes de conférence: Proceedings of the 11th Marcel Grossmann Meeting on General Relativity, vol. B p.1794-1796 (2007)
Texte intégral en Openaccess :
Ref HAL: in2p3-00126198_v1
Ref Arxiv: astro-ph/0701650
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We present here some recent results concerning scalar-tensor Dark Energy models. These models are very interesting in many respects: they allow for a consistent phantom phase, the growth of matter perturbations is modified. Using a systematic expansion of the theory at low redshifts, we relate the possibility to have phantom like DE to solar system constraints.
Commentaires: Submitted to the Proceedings of the Marcel Grossmann Conference MG11, July 2006, Berlin; 3 pages - To be published in World Scientific
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Scalar-Tensor Dark Energy Models
Auteur(s): Polarski D.
Conférence invité: Key Approaches to Dark Energy (Barcelone, ES, 2006-08-06)
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Reconstruction Methods of Dark Energy Models
Auteur(s): Polarski D.
Conférence invité: Sino-French workshop on the Dark Universe (Pekin, CN, 2006-08-27)
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Conditions for the cosmological viability of f(R) dark energy models
Auteur(s): Amendola L., Gannouji Radouane, Polarski D., Tsujikawa S.
(Article) Publié:
Physical Review D, vol. 75 p.083504 (2007)
Texte intégral en Openaccess :
Ref HAL: in2p3-00142912_v1
Ref Arxiv: gr-qc/0612180
DOI: 10.1103/PhysRevD.75.083504
WoS: 000246076900019
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
571 Citations
Résumé: 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) approx+0 and dm/dr>-1 at r approx-1. For the existence of a viable late-time acceleration we require instead either (i) m=-r-1, (sqrt{3}-1)/20 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 propto 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.
Commentaires: 25 pages, 11 figures, version to appear in Physical Review D
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Pointer states for primordial fluctuations in inflationary cosmology
Auteur(s): Kiefer C., Polarski D., Lohmar I., Starobinsky A. A.
(Article) Publié:
Classical And Quantum Gravity, vol. 24 p.1699-1718 (2007)
Texte intégral en Openaccess :
Ref HAL: in2p3-00149087_v1
Ref Arxiv: astro-ph/0610700
DOI: 10.1088/0264-9381/24/7/002
WoS: 000245514400003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
111 Citations
Résumé: Primordial fluctuations in inflationary cosmology acquire classical properties through decoherence when their wavelengths become larger than the Hubble scale. Although decoherence is effective, it is not complete, so a significant part of primordial correlations remains up to the present moment. We address the issue of the pointer states which provide a classical basis for the fluctuations with respect to the influence by an environment (other fields). Applying methods from the quantum theory of open systems (the Lindblad equation), we show that this basis is given by narrow Gaussians that approximate eigenstates of field amplitudes. We calculate both the von Neumann and linear entropy of the fluctuations. Their ratio to the maximal entropy per field mode defines a degree of partial decoherence in the entropy sense. We also determine the time of partial decoherence making the Wigner function positive everywhere which, for super-Hubble modes during inflation, is virtually independent of coupling to the environment and is only slightly larger than the Hubble time. On the other hand, assuming a representative environment (a photon bath), the decoherence time for sub-Hubble modes is finite only if some real dissipation exists.
Commentaires: 32 pages, 2 figures, matches published version: discussion expanded, references added, conclusions unchanged
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Scalar-Tensor Models of Normal and Phantom Dark Energy
Auteur(s): Gannouji Radouane, Polarski D., Ranquet Andre, Starobinsky A.A.
(Article) Publié:
Journal Of Cosmology And Astroparticle Physics, vol. 0609 p.016 (2006)
Texte intégral en Openaccess :
Ref HAL: in2p3-00115596_v1
Ref Arxiv: astro-ph/0606287
DOI: 10.1088/1475-7516/2006/09/016
WoS: 000242449600016
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
197 Citations
Résumé: 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 $p=-\rho$ at small $z$ are presented. Considering the Solar System constraints, we find for the post-Newtonian parameters that $\gamma_{PN}<1$ and $\gamma_{PN,0}\approx 1$ for the model to be viable, and $\beta_{PN,0}>1$ (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 $\Lambda$-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.
Commentaires: 30 pages, 4 figures; Matches the published version containing an expanded discussion of various points
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