Growth Rate Of Density Perturbations Research Articles

Cosmological constraints on f(Q)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(Q)$$\\end{document} gravity with redshift space distortion data

In this paper, we explore one of Einstein’s alternative formulations which involves the non-metricity scalar, Q, within the framework of f(Q) theory. Our study focuses on solving the modified Friedmann equations for the case of dust matter, ρ=ρm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\rho =\\rho _{m}$$\\end{document}, and a form of f(Q)=α+βQn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(Q) = \\alpha + \\beta Q^n$$\\end{document}. We investigate the behavior of our model in both linear (n=1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n=1)$$\\end{document} and nonlinear (n≠1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n\ e 1)$$\\end{document} scenarios at the background and perturbation levels. By employing the Markov chain Monte Carlo (MCMC) method, we constrain our model using observational datasets including redshift space distortion, cosmic chronometers, and Pantheon+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^+$$\\end{document}. Without using any parameterization of the growth rate index which quantifies the deviation from the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM model, both models exhibit good accuracy in describing the redshift space distortion. We further analyze the dynamics of the Universe using cosmography parameters, where our model exhibits a phase transition between deceleration and acceleration phases at z=0.789\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z=0.789$$\\end{document}. Our findings reveal that our model exhibits a phantom-like behavior based on statefinder diagnostic analysis. Interestingly, the model demonstrates a rich variety of behaviors, resembling either a quintessence-like scenario for (n<1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n<1)$$\\end{document} or phantom-like scenario for (n≥1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n\\ge 1)$$\\end{document}. Using the MCMC best fit and parameterizing the growth index, the evolution of the growth index also depends on the parameter n, either remaining constant (in the linear case) or showing a decreasing trend (in the nonlinear case), indicating a weaker growth rate of density perturbations during earlier cosmic times. Finally, we compare our findings of the growth index with the values obtained in the literature.

Observational tests of the Glavan, Prokopec and Starobinsky model of dark energy

In the last dozens of years different data sets revealed the accelerated expansion of the Universe which is driven by the so called dark energy, that now dominates the total amount of matter-energy in the Universe. In a recent paper Glavan, Prokopec and Starobinsky propose an interesting model of dark energy, which traces the Universe evolution from the very early quantum era to the present time. Here we perform a high-redshift analysis to check if this new model is compatible with present day observational data and compare predictions of this model with that of the standard varLambda CDM cosmological model. In our analysis we use only the most reliable observational data, namely the distances to selected SNIa, GRB Hubble diagram, and 28 direct measurements of the Hubble constant. Moreover we consider also non geometric data related to the growth rate of density perturbations. We explore the probability distributions of the cosmological parameters for both models. To build up their own regions of confidence, we maximize the appropriate likelihood functions using the Markov chain Monte Carlo (MCMC) method. Our statistical analysis indicates that these very different models of dark energy are compatible with present day observational data and the GPS model seems slightly favored with respect to the varLambda hbox {CDM model}. However to further restrict different models of dark energy it will be necessary to increase the precision of the Hubble diagram at high redshifts and to perform more detailed analysis of the influence of dark energy on the process of formation of large scale structure.

Configuration entropy in the ΛCDM and the dynamical dark energy models: Can we distinguish one from the other?

The evolution of the configuration entropy of the mass distribution in the Universe is known to be governed by the growth rate of density perturbations and the expansion rate of the Universe. We consider the $\Lambda$CDM model and a set of dynamical dark energy models with different parametrization of the equation of state and explore the evolution of the configuration entropy in these models. We find that the nature of evolution of the configuration entropy depends on the adopted parametrization which may allow us to discern them from each other. The configuration entropy initially decreases with time but nearly plateaus out at present in the $\Lambda$CDM model. The models where dark energy becomes less dominant at late times exhibit a larger decrease in the configuration entropy compared to the $\Lambda$CDM model after redshift $z \sim 1$. We find that the configuration entropy remains nearly unchanged in the models where dark energy becomes more dominant at late times. Our results suggest that the method presented here may be also used to constrain the initial value of the configuration entropy of the Universe.

No evidence for modifications of gravity from galaxy motions on cosmological scales

The recent discovery of gravitational waves marks the culmination of a sequence of successful tests of the general theory of relativity (GR) since its formulation in 1915. Yet these tests remain confined to the scale of stellar systems or the strong gravity regime. A departure from GR on larger, cosmological scales has been advocated by the proponents of modified gravity theories as an alternative to the Cosmological Constant to account for the observed cosmic expansion history. While indistinguishable in these terms by construction, such models on the other hand yield distinct values for the linear growth rate of density perturbations and, as a consequence, for the associated galaxy peculiar velocity field. Measurements of the resulting anisotropy of galaxy clustering, when spectroscopic redshifts are used to derive distances, have thus been proposed as a powerful probe of the validity of GR on cosmological scales. However, despite significant effort in modelling such redshift space distortions, systematic errors remain comparable to current statistical uncertainties. Here, we present the results of a different forward-modelling approach, which fully exploits the sensitivity of the galaxy velocity field to modifications of GR. We use state-of-the-art, high-resolution N-body simulations of a standard GR and a compelling f(R) model, one of GR's simplest variants, to build simulated catalogues of stellar-mass-selected galaxies through a robust match to the Sloan Digital Sky Survey observations. We find that, well within the uncertainty of this technique, f(R) fails to reproduce the observed redshift-space clustering on scales 1-10 Mpc/h. Instead, the standard LCDM GR model agrees impressively well with the data. This result provides a strong confirmation, on cosmological scales, of the robustness of Einstein's general theory of relativity.

Large-scale peculiar velocities through the galaxy luminosity function at z ~ 0.1

AbstractPeculiar motion introduces systematic variations in the observed luminosity distribution of galaxies. This allows one to constrain the cosmic peculiar velocity field from large galaxy redshift surveys. Using around half a million galaxies from the SDSS Data Release 7 at z ~ 0.1, we demonstrate the applicability of this approach to large datasets and obtain bounds on peculiar velocity moments and σ8, the amplitude of the linear matter power spectrum. Our results are in good agreement with the ΛCDM model and consistent with the previously reported ~ 1% zero-point tilt in the SDSS photometry. Finally, we discuss the prospects of constraining the growth rate of density perturbations by reconstructing the full linear velocity field from the observed galaxy clustering in redshift space.

Testing General Relativity with the Multipole Spectra of the SDSS Luminous Red Galaxies

As a test of general relativity on cosmological scales, we measure the γ parameter for the growth rate of density perturbations using the redshift-space distortion of the luminous red galaxies in the Sloan Digital Sky Survey (SDSS). Assuming the cosmological constant model, which matches the results of the WMAP experiment, we find γ = 0.62+1.8(σ8 − 0.8)± 0.11 at 1-sigma confidence level, which is consistent with the prediction of general relativity, γ 0.55 ∼ 0.56. Rather high value of σ8(≥ 0.87) is required to be consistent with the prediction of the cosmological DGP model, γ 0.68.

Accelerating universe and scalar-tensor theories

Observational probes of dark energy converge on the fact that its equation of state w is close to −1. Some of these probes (for example the Gold SnIa sample) mildly support the possibility that w is time dependent and crosses the phantom divide line w = −1. Such a crossing is inconsistent with dark energy in the form of a single minimally coupled scalar field for any form of the field Lagrangian. The simplest theoretically motivated theories that are consistent with such crossing of the phantom divide are scalar-tensor extensions of general relativity. Therefore the crossing of the phantom divide if confirmed by future observations could be viewed as an indication hinting towards extensions of general relativity. Alternative signatures of extended gravity theories can be traced in the growth rate of density perturbations at recent redshifts as observed recently by the 2dFGRS.

Perturbations in a spherically symmetric inhomogeneous cosmological model with the self-similar region

To clarify the evolution of inhomogeneous substructures in large-scale structures such as voids, we study the perturbations in a spherically symmetric inhomogeneous model with the self-similar region outside the inner low-density homogeneous region, first based on the Gerlach-Sengupta general-relativistic formulation for perturbations in spherically symmetric inhomogeneous models. Owing to self-similarity, the analysis for all kinds of perturbations at the early stage is simplified in a similar way to homogeneous models. Next we take the approximate treatment due to the local homogeneous model with the average density parameter which is considered at each point, in order to study the behavior of perturbations on small scales. It is found that the growth rate of density perturbations in the outside self-similar region can be larger by about $30\ensuremath{-}20%$ (for $z=2\ensuremath{-}3)$ than that in the corresponding ordinary low-density homogeneous model.

Gauge-invariant cosmological perturbations in generalized Einstein theories

Using the covariant approach and conformal transformations, we present a gauge-invariant formalism for cosmological perturbations in generalized Einstein theories (GETs), including the Brans-Dicke theory, theories with a non-minimally coupled scalar field and certain curvature-squared theories. We find an enhancement in the growth rate of density perturbations in the Brans-Dicke theory, and discuss attractive features of GETs in the structure formation process.

Inhomogeneous mixmaster universes: Some exact solutions

Algorithms for generating new exact solutions of the Einstein-Klein-Gordon field equations, which describe inhomogeneous universes with S 3 topology of spatial sections, are developed. The known exact vacuum and stiff-fluid solutions with S 3 topology are used as an input. The methods developed are further applied to derive inhomogenous generalizations of Bianchi type IX solutions and inhomogeneous S 3 Gowdy models with gravitational and scalar waves. It is shown that the new solutions, which are generalizations of the Bianchi type IX models, permit identification of the scalar field with the velocity potential of the stiff irrotational fluid. The latter result is further used to study the growth rate of density perturbations of the isotropic and anisotropic Bianchi type IX universes in a fully nonlinear relativistic regime. The role of anisotropy of the rate of growth of density perturbations is studied in detail.