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Register a new userThe impact of dark energy perturbations on the growth index
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Added by
Ronaldo Carlotto Batista
Publication date
2014
fields
Physics
and research's language is
English
Authors
Ronaldo C. Batista
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We show that in clustering dark energy models the growth index of linear matter perturbations, $gamma$, can be much lower than in $Lambda$CDM or smooth quintessence models and present a strong variation with redshift. We find that the impact of dark energy perturbations on $gamma$ is enhanced if the dark energy equation of state has a large and rapid decay at low redshift. We study four different models with these features and show that we may have $0.33<gammaleft(zright)<0.48$ at $0<z<3$. We also show that the constant $gamma$ parametrization for the growth rate, $f=dlndelta_{m}/dln a=Omega_{m}^{gamma}$, is a few percent inaccurate for such models and that a redshift dependent parametrization for $gamma$ can provide about four times more accurate fits for $f$. We discuss the robustness of the growth index to distinguish between General Relativity with clustering dark energy and modified gravity models, finding that some $fleft(Rright)$ and clustering dark energy models can present similar values for $gamma$.
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We study how the cosmological constraints from growth data are improved by including the measurements of bias from Dark Energy Survey (DES). In particular, we utilize the biasing properties of the DES Luminous Red Galaxies (LRGs) and the growth data provided by the various galaxy surveys in order to constrain the growth index ($gamma$) of the linear matter perturbations. Considering a constant growth index we can put tight constraints, up to $sim 10%$ accuracy, on $gamma$. Specifically, using the priors of the Dark Energy Survey and implementing a joint likelihood procedure between theoretical expectations and data we find that the best fit value is in between $gamma=0.64pm 0.075$ and $0.65pm 0.063$. On the other hand utilizing the Planck priors we obtain $gamma=0.680pm 0.089$ and $0.690pm 0.071$. This shows a small but non-zero deviation from General Relativity ($gamma_{rm GR}approx 6/11$), nevertheless the confidence level is in the range $sim 1.3-2sigma$. Moreover, we find that the estimated mass of the dark-matter halo in which LRGs survive lies in the interval $sim 6.2 times 10^{12} h^{-1} M_{odot}$ and $1.2 times 10^{13} h^{-1} M_{odot}$, for the different bias models. Finally, allowing $gamma$ to evolve with redshift [Taylor expansion: $gamma(z)=gamma_{0}+gamma_{1}z/(1+z)$] we find that the $(gamma_{0},gamma_{1})$ parameter solution space accommodates the GR prediction at $sim 1.7-2.9sigma$ levels.
In this work, we study the extended viscous dark energy models in the context of matter perturbations. To do this, we assume an alternative interpretation of the flat Friedmann-Lema^itre-Robertson-Walker Universe, through the nonadditive entropy and the viscous dark energy. We implement the relativistic equations to obtain the growth of matter fluctuations for a smooth version of dark energy. As result, we show that the matter density contrast evolves similarly to the $Lambda$CDM model in high redshift; in late time, it is slightly different from the standard model. Using the latest geometrical and growth rate observational data, we carry out a Bayesian analysis to constrain parameters and compare models. We see that our viscous models are compatible with cosmological probes, and the $Lambda$CDM recovered with a $1sigma$ confidence level. The viscous dark energy models relieve the tension of $H_0$ in $2 sim 3 sigma$. Yet, by involving the $sigma_8$ tension, some models can alleviate it. In the model selection framework, the data discards the extended viscous dark energy models.
We derive for the first time the growth index of matter perturbations of the FLRW flat cosmological models in which the vacuum energy depends on redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which apart from a leading constant term $Lambda_0$ there is also a $H^{2}$-dependence in the functional form of vacuum, namely $Lambda(H)=Lambda_{0}+3 u (H^{2}-H^{2}_{0})$. Since $| u|ll1$ this form endows the vacuum energy of a mild dynamics which affects the evolution of the main cosmological observables at the background and perturbation levels. Specifically, at the perturbation level we find that the growth index of the running vacuum cosmological model is $gamma_{Lambda_{H}} approx frac{6+3 u}{11-12 u}$ and thus it nicely extends analytically the result of the $Lambda$CDM model, $gamma_{Lambda}approx 6/11$.
In this paper we study the evolution of cosmological perturbations in the presence of dynamical dark energy, and revisit the issue of dark energy perturbations. For a generally parameterized equation of state (EoS) such as w_D(z) = w_0+w_1frac{z}{1+z}, (for a single fluid or a single scalar field ) the dark energy perturbation diverges when its EoS crosses the cosmological constant boundary w_D=-1. In this paper we present a method of treating the dark energy perturbations during the crossing of the $w_D=-1$ surface by imposing matching conditions which require the induced 3-metric on the hypersurface of w_D=-1 and its extrinsic curvature to be continuous. These matching conditions have been used widely in the literature to study perturbations in various models of early universe physics, such as Inflation, the Pre-Big-Bang and Ekpyrotic scenarios, and bouncing cosmologies. In all of these cases the EoS undergoes a sudden change. Through a detailed analysis of the matching conditions, we show that delta_D and theta_D are continuous on the matching hypersurface. This justifies the method used[1-4] in the numerical calculation and data fitting for the determination of cosmological parameters. We discuss the conditions under which our analysis is applicable.
We investigate the Tsallis holographic dark energy (THDE) models in the context of perturbations growth. We assume the description of dark energy by considering the holographic principle and the nonadditive entropy to carry out this. We implement the perturbed relativistic equations to achieve the growth of matter fluctuations, being the growth rate of the cosmic structures is non-negligible at low redshifts. To constrain and compare the models, we carry out the Bayesian analysis using the recent geometrical and growth rate observational data. The main results are: (i) the models are compatible with cosmological observations, (ii) the cosmological constant recovered with a $1sigma$ confidence level, furthermore (iii) they could cross the phantom barrier. Finally, the models can relieve $approx 1sigma$ the $sigma_8$ tension in the non-clustered case and can alleviate in $approx 2.8sigma$ the $H_0$ tension. From the model selection viewpoint, the data discarded the THDE models.
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