Growth Of Matter Density Perturbations Research Articles

Cosmic and growth matter analysis of deformed Hořava–Lifshitz gravity

Hořava–Lifshitz gravity is a very fascinating proposal of modified gravity for explaining the current acceleration and other cosmic issues. In continuation to this discussion, we explore the consequences of Tsallis dark energy with Hubble and particle horizons in the framework of deformed Hořava–Lifshitz gravity for flat FRW universe. The interaction between Tsallis holographic dark energy and dark matter is also taken into account to discuss the underlying scenario. It is found that fractional dark energy density ([Formula: see text]) approaches to [Formula: see text] as redshift goes to zero (present epoch) for both cases of horizons. The cosmic parameter ([Formula: see text]) shows phantom crossing behavior in both models, i.e. it evolutes the universe from quintessence phase to phantom phase by crossing the vacuum horizon. In both cases of horizons, the deceleration supports the cosmic acceleration by exhibiting the negative values. The perturbation sound speed also favors the viability of our models through positive behavior. The coincidence parameter supports the exchange of dark matter to dark energy phenomenon through positivity. We also discuss the behavior of growth rate and growth index in the growth of matter density perturbations for both horizons. These parameters mimic the [Formula: see text]CDM behavior of the universe.

Growth of matter density perturbations in 4D Einstein–Gauss–Bonnet gravity

Recently, a novel Einstein-Gauss-Bonnet gravity in four dimensions has been introduced [Phys. Rev. Lett. 124 (2020) 081301]. We will investigate cosmological consequences of this model in details. We will consider linear matter density perturbations and also estimate relevant modified gravity parameters. Specially we will concentrate on the growth rate of non-relativistic matter perturbations on top of FRW geometry and show that for a narrow range of the Gauss-Bonnet coupling constant, observational data will be satisfied. In this paper, it is shown that for enough large values of the coupling constant, the suggested $\sigma_8$ will become greater than $\Lambda$CDM value.

Cannibal dark matter and large scale structure

Cannibals are dark matter particles with a scattering process that allows three particles to annihilate to two. This exothermic process keeps the gas of the remaining particles warm long after they become nonrelativistic. A cannibalizing dark sector which is decoupled from the standard model naturally arises from a pure-glue confining hidden sector. It has an effective field theory description with a single massive interacting real scalar field, the lightest glueball. Since warm dark matter strongly suppresses the growth of structure, cannibals cannot be all of the dark matter. Thus, we propose a scenario where most dark matter is noninteracting and cold but about 1 percent is cannibalistic. We review the cannibals' unusual scaling of the temperature and energy and number densities with redshift and generalize the equations for the growth of matter density perturbations to the case of cannibals. We solve the equations numerically to predict the scaling of the Hubble parameter and the characteristic shape of the linear matter power spectrum as a function of model parameters. Our results may have implications for the ${\ensuremath{\sigma}}_{8}$ and ${H}_{0}$ problems.

Evidence for dark matter interactions in cosmological precision data?

We study a two-parameter extension of the cosmological standard model ΛCDM in which cold dark matter interacts with a new form of dark radiation. The two parameters correspond to the energy density in the dark radiation fluid ΔNfluid and the interaction strength between dark matter and dark radiation. The interactions give rise to a very weak ``dark matter drag'' which damps the growth of matter density perturbations throughout radiation domination, allowing to reconcile the tension between predictions of large scale structure from the CMB and direct measurements of σ8. We perform a precision fit to Planck CMB data, BAO, large scale structure, and direct measurements of the expansion rate of the universe today. Our model lowers the χ-squared relative to ΛCDM by about 12, corresponding to a preference for non-zero dark matter drag by more than 3σ. Particle physics models which naturally produce a dark matter drag of the required form include the recently proposed non-Abelian dark matter model in which the dark radiation corresponds to massless dark gluons.

Evolution of matter density perturbations in [formula omitted] theories of gravity with non-minimal coupling between matter and geometry

In the context of f(R) theories of gravity with non-minimal coupling between matter and geometry, we study the evolution of scalar cosmological perturbations in the metric formalism. We not only derive the perturbation equations in the longitudinal gauge, but also obtain the equation of matter density perturbations by using both the perturbed covariant conservation equations which are subject to taking the Lagrangian density of matter as opposite to the energy density of a perfect fluid, and the subhorizon approximation. Furthermore, in order to investigate the behavior of matter density perturbations, we apply the obtained perturbation equation to a class of models. In these models, it is shown that 1) the stronger the non-minimal coupling between matter and geometry is, the more the growth of matter density perturbations slows down; 2) the small scale perturbations grows faster than the large ones; and 3) the more the deviation of parameter n or λ from zero gets, the more evident the scale dependence of the growth of matter density perturbations becomes.

Cosmological perturbations in theories with non-minimal coupling between curvature and matter

In this work, we examine how the presence of a non-minimal coupling between spacetime curvature and matter affects the evolution of cosmological perturbations on a homogeneous and isotropic Universe, and hence the formation of large-scale structure. This framework places constraints on the terms which arise due to the coupling with matter and, in particular, on the modified growth of matter density perturbations. We derive approximate analytical solutions for the evolution of matter overdensities during the matter dominated era and discuss the compatibility of the obtained results with the hypothesis that the late time acceleration of the Universe is driven by a non-minimal coupling.

Growth of matter perturbations for realisticF(R)models

Two different realistic $F(R)$ modified gravity models are considered in the framework of the Friedmann-Lemetre-Robertson-Walker universe. The parameters of these two models are adjusted to reach coherence with the most recent and accurate observations of the current Universe. A study of the growth of matter density perturbations is done, and several parametrizations of the growth index are developed for both models. The ansatz for the growth index given by $\ensuremath{\gamma}={\ensuremath{\gamma}}_{0}+{\ensuremath{\gamma}}_{1}z/(1+z)$ seems to be the best parametrization for the two models considered. Finally, the values obtained for ${\ensuremath{\gamma}}_{0}$ and ${\ensuremath{\gamma}}_{1}$ can be used in order to characterize these two models and to differentiate them from others such as the Hu-Sawicki model.

Confronting dark energy models mimicking ΛCDM epoch with observational constraints: Future cosmological perturbations decay or future Rip?

We confront dark energy models which are currently similar to ΛCDM theory with observational data which include the SNe data, matter density perturbations and baryon acoustic oscillations data. DE cosmology under consideration may evolve to Big Rip, type II or type III future singularity, or to Little Rip or Pseudo-Rip universe. It is shown that matter perturbations data define more precisely the possible deviation from ΛCDM model than consideration of SNe data only. The combined data analysis proves that DE models under consideration are as consistent as ΛCDM model. We demonstrate that growth of matter density perturbations may occur at sufficiently small background density but still before the possible disintegration of bound objects (like clusters of galaxies, galaxies, etc.) in Big Rip, type III singularity, Little Rip or Pseudo-Rip universe. This new effect may bring the future universe to chaotic state well before disintegration or Rip.

Linear perturbations in Galileon gravity models

We study the cosmology of Galileon modified gravity models in the linear perturbation regime. We derive the fully covariant and gauge invariant perturbed field equations using two different methods, which give consistent results, and solve them using a modified version of the {\tt CAMB} code. We find that, in addition to modifying the background expansion history and therefore shifting the positions of the acoustic peaks in the cosmic microwave background (CMB) power spectrum, the Galileon field can cluster strongly from early times, and causes the Weyl gravitational potential to grow, rather than decay, at late times. This leaves clear signatures in the low-$l$ CMB power spectrum through the modified integrated Sachs-Wolfe effect, strongly enhances the linear growth of matter density perturbations and makes distinctive predictions for other cosmological signals such as weak lensing and the power spectrum of density fluctuations. The quasi-static approximation is shown to work quite well from small to the near-horizon scales. We demonstrate that Galileon models display a rich phenomenology due to the large parameter space and the sensitive dependence of the model predictions on the Galileon parameters. Our results show that some Galileon models are already ruled out by present data and that future higher significance galaxy clustering, ISW and lensing measurements will place strong constraints on Galileon gravity.

Linear Growth of Matter Density Perturbations in Theories

We derive the equation of matter density perturbations on sub-horizon scales around a flat Friedmann-Lemaˆ itre-Robertson-Walker background for the general Lagrangian density f (R, G) that is a function of a Ricci scalar R and a Gauss-Bonnet term G. We find that the effective gravitational constant generically scales as distance squared at small distances. The effect of this diminishing of the gravitational constant might be important in the gravitational dynamics of cosmic objects such as galaxies, which can be in principle tested by observations. We also provide the general expressions for the effective anisotropic stress, which is useful to constrain modified gravity models from observations of large-scale structure and weak lensing. We also find that there is a special class of theories which evade this unusual behaviour and that the condition to belong to this special class is exactly the same as the one for not having super-luminal modes with propagation speed proportional to their wavenumber. Subject Index: 453

Cosmic perturbations with running G and Λ

Cosmologies with running cosmological term ρΛ and gravitational Newton's coupling G may naturally be expected if the evolution of the universe can ultimately be derived from the first principles of quantum field theory or string theory. For example, if matter is conserved and the vacuum energy density varies quadratically with the expansion rate as ρΛ(H) = n0 + n2 H2, with n0 ≠ 0 (a possibility that has been advocated in the literature within the QFT framework), it can be shown that G must vary logarithmically (hence very slowly) with H. In this paper, we derive the general cosmological perturbation equations for models with variable G and ρΛ in which the fluctuations δG and δρΛ are explicitly included. We demonstrate that if matter is covariantly conserved, the late growth of matter density perturbations is independent of the wavenumber k. Furthermore, if ρΛ is negligible at high redshifts and G varies slowly, we find that these cosmologies produce a matter power spectrum with the same shape as that of the ΛCDM model, thus predicting the same basic features on structure formation. Despite this shape indistinguishability, the free parameters of the variable G and ρΛ models can still be effectively constrained from the observational bounds on the spectrumamplitude.

Dispersion of growth of matter perturbations inf(R)gravity

We study the growth of matter density perturbations ${\ensuremath{\delta}}_{m}$ for a number of viable $f(R)$ gravity models that satisfy both cosmological and local gravity constraints, where the Lagrangian density $f$ is a function of the Ricci scalar $R$. If the parameter $m\ensuremath{\equiv}R{f}_{,RR}/{f}_{,R}$ today is larger than the order of ${10}^{\ensuremath{-}6}$, linear perturbations relevant to the matter power spectrum evolve with a growth rate $s\ensuremath{\equiv}d\mathrm{ln}{\ensuremath{\delta}}_{m}/d\mathrm{ln}a$ ($a$ is the scale factor) that is larger than in the $\ensuremath{\Lambda}\mathrm{CDM}$ model. We find the window in the free parameter space of our models for which spatial dispersion of the growth index ${\ensuremath{\gamma}}_{0}\ensuremath{\equiv}\ensuremath{\gamma}(z=0)$ ($z$ is the redshift) appears in the range of values $0.40\ensuremath{\lesssim}{\ensuremath{\gamma}}_{0}\ensuremath{\lesssim}0.55$, as well as the region in parameter space for which there is essentially no dispersion and ${\ensuremath{\gamma}}_{0}$ converges to values around $0.40\ensuremath{\lesssim}{\ensuremath{\gamma}}_{0}\ensuremath{\lesssim}0.43$. These latter values are much lower than in the $\ensuremath{\Lambda}\mathrm{CDM}$ model. We show that these unusual dispersed or converged spectra are present in most of the viable $f(R)$ models with $m(z=0)$ larger than the order of ${10}^{\ensuremath{-}6}$. These properties will be essential in the quest for $f(R)$ modified gravity models using future high-precision observations and they confirm the possibility to distinguish clearly most of these models from the $\ensuremath{\Lambda}\mathrm{CDM}$ model.

Evolution of scalar perturbations in cosmology with quintessential dark energy

The dynamics of expansion of the Universe and evolution of scalar perturbations are studied for the quintessential scalar fields $Q$ with the classical Lagrangian satisfying the additional condition $w=const$ or $c^2_a=0$. Both quintessential fields are studied for the same cosmological model. The systems of evolutionary equations for gauge-invariant perturbations of metrics, matter and quintessence have been analysed analyticaly for the early stage of the Universe life and numerically up to the present epoch. It is shown that amplitudes of the adiabatic matter density perturbations grow like in $\Lambda$CDM-model but time dependences of amplitudes of the quintessence perturbations are more varied: gauge-invariant variables $D_g^{(Q)}$ and $D_s^{(Q)}$ decay from initial constant value after entering the particle horizon while $D^{(Q)}$ and $V^{(Q)}$ grow at the early stage before entering the horizon and decay after that -- in the quintessence-dominated epoch, when gravitational potential starts to decay -- so, that at the current epoch they are approximately two orders lower than matter ones at the supercluster scale. Therefore, at the subhorizon scales the quintessential scalar fields are smoothed out while the matter clusters. It is also shown that both quintessential scalar fields suppress the growth of matter density perturbations and the amplitude of gravitational potential. In these QCDM-models -- unlike $\Lambda$CDM ones -- such suppression is scale dependent and more visible for the quintessence with $c^2_a=0$.

Effective growth of matter density fluctuations in the runningΛ CDMand Λ XCDM models

We investigate the matter density fluctuationsδρM/ρM for two dark energy (DE) models in the literature in which the cosmological termΛ is a running parameter. In the first model, the runningΛCDM model, matter and DE exchange energy, whereas in the second model, theΛXCDM model, the total DE and matter components are conserved separately. TheΛXCDM model was proposed as an interesting solution to the cosmic coincidenceproblem. It includes an extra dynamical component, the ‘cosmon’X, which interactswith the running Λ, but not with matter. In our analysis we make use of the current value of the linear bias parameter,b2(0) = PGG/PMM, where is the present matter power spectrum andPGG is the galaxy fluctuation power spectrum. The former can be computed withina given model, and the latter is found from the observed LSS data (at smallz) obtained by the 2dF Galaxy Redshift Survey. It is found that within a 10% accuracyfor the standard ΛCDM model. Adopting this limit for any DE model and using a method based on the effective equationof state for the DE, we can set a limit on the growth of matter density perturbations for the runningΛCDM model,the solution of which is known. This provides a good test of the procedure, which we then apply to theΛXCDM modelin order to determine the physical region of parameter space, compatible with the LSS data. In this region,the ΛXCDM model is consistent with known observations and provides at the same time a viablesolution to the cosmic coincidence problem.

Matter density perturbations in interacting quintessence models

Models with dark energy decaying into dark matter have been proposed to solve the coincidence problem in cosmology. We study the effect of such coupling in the matter power spectrum. Because of the interaction, the growth of matter density perturbations during the radiation dominated regime is slower compared to noninteracting models with the same ratio of dark matter to dark energy today. This effect introduces a damping on the power spectrum at small scales proportional to the strength of the interaction, ${c}^{2}$, and similar to the effect generated by ultrarelativistic neutrinos. The interaction also shifts matter-radiation equality to larger scales. We compare the matter power spectrum of interacting quintessence models with the measurments of the 2-degree field galaxy redshift survey (2dFGRS). The data are insensitive to values of ${c}^{2}\ensuremath{\le}{10}^{\ensuremath{-}3}$ but strongly constrain larger values. We particularize our study to models that during radiation domination have a constant dark matter to dark energy ratio.

Anisotropies of the cosmic background radiation by domain wall networks

view Abstract Citations (8) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Anisotropies of the Cosmic Background Radiation by Domain Wall Networks Nambu, Yasusada ; Ishihara, Hideki ; Gouda, Naoteru ; Sugiyama, Naoshi Abstract We discuss cosmological effects by domain wall formation associated with a late time phase transition after decoupling. Assuming the existence of rigid domain wall networks, we construct a simple one-dimensional model and calculate the quadrupole anisotropy of the cosmic background radiation (CBR). Contrary to one's naive expectation, the gravitational potential of a domain wall itself does not disturb the anisotropy of CBR. Estimating the quadrupole anisotropy of CBR induced by the wall driven growth of matter density perturbations, a 100h^-1^ Mpc periodic wall structure is found to be consistent with the observed upper bound. Publication: The Astrophysical Journal Pub Date: May 1991 DOI: 10.1086/186045 Bibcode: 1991ApJ...373L..35N Keywords: Anisotropy; Background Radiation; Cosmology; Domain Wall; Relic Radiation; Astronomical Models; Computational Astrophysics; Density Distribution; Phase Transformations; Space Radiation; COSMIC BACKGROUND RADIATION; COSMOLOGY full text sources ADS |