Growth Of Matter Perturbations Research Articles

Growth of matter perturbations in the interacting dark energy-dark matter scenarios

Growth of matter perturbations in the interacting dark energy-dark matter scenarios

Cosmological evolution in bimetric gravity: observational constraints and LSS signatures

Bimetric gravity is an interesting alternative to standard GR given its potential to provide a concrete theoretical framework for a ghost-free massive gravity theory. Here we investigate a class of Bimetric gravity models for their cosmological implications. We study the background expansion as well as the growth of matter perturbations at linear and second order. We use low-redshift observations from SnIa (Pantheon+ and SH0ES), Baryon Acoustic Oscillations (BAO), the growth (fsigma _{8}) measurements and the measurement from Megamaser Cosmology Project to constrain the Bimetric model. We find that the Bimetric models are consistent with the present data alongside the Lambda CDM model. We reconstructed the “ effective dark energy equation of state”(omega _{de}) and “Skewness”(S_{3}) parameters for the Bimetric model from the observational constraints and show that the current low-redshift data allow significant deviations in omega _{de} and S_{3} parameters with respect to the Lambda CDM behaviour. We also look at the ISW effect via galaxy-temperature correlations and find that the best fit Bimetric model behaves similarly to Lambda CDM in this regard.

Linear growth of structure in massive gravity

We study background dynamics and the growth of matter perturbations in the extended quasidilaton setup of massive gravity. For the analysis of perturbations, we first choose a scalar field matter component and obtain the conditions under which all scalar perturbations are stable. We work in unitary gauge for the matter field, which allows us to directly map to known results in the limit of general relativity. By performing a parameter search, we find that the perturbations are unstable in general, while a particular choice of potential, where the scalar field effectively behaves like pressureless matter, allows for stable perturbations. We next consider the growth of matter perturbations in a cold dark matter-dominated Universe. Working in conformal Newtonian gauge, we obtain evolution equations for various observables including the growth factor and growth rate, and find scale-independent growth in the quasistatic and subhorizon approximations. We finally show how the Hubble parameter and matter perturbations evolve in massive gravity for a specific choice of parameter values, and how this evolution compares to the standard cosmological model consisting of a cosmological constant and cold dark matter.

Two-parametric f(R) dark energy model and some observational constraints

A modified [Formula: see text] viable model is proposed that behaves asymptotically as [Formula: see text]CDM and satisfies cosmological and local gravity constraints. Apart from a mass scale that is a priori defined, the model contains only one additional parameter, which is determined by the current value of the matter density parameter [Formula: see text]. Under the chameleon mechanism the model satisfies the thin shell restrictions for local gravity systems without imposing additional restrictions on model parameters. Signals of scalar–tensor regime in the growth of matter perturbations, are present. Using the mass scale to determine the matter density parameter today, the remaining free parameter covers the whole range of values needed to test the model against the more stringent constraints arising at galactic and galactic cluster scales. The finite time singularity of the model was analyzed. A comparison was made with known models with the same number of parameters.

Growth of matter perturbations in the extended viscous dark energy models

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–Lemaître–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; however, 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.

Non-minimal energy\u2013momentum squared gravity

We consider a gravitational theory with an additional non-minimal coupling between baryonic matter fields and geometry. The coupling is second order in the energy momentum tensor and can be seen as a generalization of the energy–momentum squared gravity model. We will add a constraint through a Lagrange multiplier to ensure the conservation of the energy–momentum tensor. Background cosmological implications together with its dynamical system analysis will be investigated in details. Also we will consider the growth of matter perturbations at first order, and estimate the model parameter from observations on H and also fsigma _8. We will show that the model parameter should be small and positive in 2sigma confidence interval. The theory is shown to be in a good agreement with observational data.

Growth of matter perturbations in the bi-Galileons field model

We study a dark energy cubic bi-Galileons field model based on truncation of the recently proposed generalized covariant multi-Galileons model. We investigate the cosmological dynamic of the model by the theory of dynamical systems through the analysis of the properties of the fixed points in each cosmological epoch. We show the existence of two tracker solutions, one of which is that of the cubic single Galileon model and the other solution is the signature of the second Galileon field. Exploiting the competition between the two Galileon fields, we find a dark energy solution that avoids the approach to the tracker solution with dark energy equation of state $w_{DE}=-2$ during the matter epoch which is disfavored by the observational data. We study also the growth rate of matter perturbations. Using recent $f\sigma_{8}$ redshift space distortion (RSD) and model-independent observational Hubble (OHD) data sets, we place observational constraints on the coupling constant and cosmological parameters of the bi-Galileons model through Monte Carlo numerical method based on the Metropolis-Hastings algorithm. We find that the amplitude of growth matter fluctuations is consistent with the Planck15 data and ease the tension between early and later clustering, and fits better the data from the DES survey over the data from KiDS-450 survey. We also find that the best fit value for the Hubble constant is compatible with new measurements of Cepheid-supernovae distance scale. Finally, we perform a model selection through the Bayes factor and found that the bi-Galileons model is disfavored in comparison to the $\Lambda$CDM model, but slightly preferred to $w$CDM model.

Imprint of a Steep Equation of State in the growth of structure

We study the cosmological properties of a dynamical of dark energy (DE) component determined by a Steep Equation of State (SEoS) w(z)=w0+wi(z/zT)q1+(z/zT)q. The SEoS has a transition at zT between two pivotal values (wi, w0) which can be taken as an early time and present day values of w and the steepness is given by q. We describe the impact of this dynamical DE at background and perturbative level. The steepness of the transition has a better cosmological fit than a conventional CPL model with w=w0+wa(1−a). Furthermore, we analyze the impact of steepness of the transition in the growth of matter perturbations and structure formation. This is manifest in the linear matter power spectrum, P(k), the logarithmic growth function, fσ8(z), and the differential mass function dn/dlogM(z=0). The differences in these last three quantities is at a percent-level using the same cosmological baseline parameters in our SEoS and a ΛCDM model. However, we find an increase in the power spectrum, producing a bump at k ≈ kT with kT ≡ aTH(aT) the mode associated to the time of the steep transition (aT=1/(1+zT)). Different dynamics of DE lead to a different amount of DM at present time which has an impact in Power Spectrum and accordingly in structure formation.

$\Lambda$CDM-like models with future singularities

We consider new models of dark energy with finite time future singularities, by introducing the pressure density as a function of the scale factor. This approach gives acceptable phenomenological models of dark energy, that resemble that of the cosmological constant up to the present, which face future singularities at finite time and finite scale factor. Exact scalar field model representation was found for quintessence, Big Rip and type III singularity models. The simple form of the equation of state allows to establish a relationship between its current value, w0, and the time or redshift at which the singularity takes place. The effect on the growth of matter perturbations is analyzed.

Growth of matter perturbations in nonminimal teleparallel dark energy

We study the growth rate of matter perturbations in the context of teleparallel dark energy in a flat universe. We investigate the dynamics of different theoretical scenarios based on specific forms of the scalar field potential. Allowing for non-minimal coupling between torsion scalar and scalar field, we perform a phase-space analysis of the autonomous systems of equations through the study of critical points. We thus analyze the stability of the critical points, and discuss the cosmological implications searching for possible attractor solutions at late times. Furthermore, combing the growth rate data and the Hubble rate measurements, we place observational constraints on the cosmological parameters of the models through Monte Carlo numerical method. We find that the scenario with a non-minimal coupling is favoured with respect to the standard quintessence case. Adopting the best-fit results, we show that the dark energy equation of state parameter can cross the phantom divide. Finally, we compare our results with the predictions of the concordance $\Lambda$CDM paradigm by performing Bayesian model selection.

Dark energy in scalar-vector-tensor theories

The scalar-vector-tensor theories with second-order equations of motion can accommodate both Horndeski and generalized Proca theories as specific cases. In the presence of a perfect fluid, we study the cosmology in such a most general scheme of scalar-vector-tensor theories with parity invariance by paying particular attention to the application to dark energy. We obtain a closed-form expression of the background equations of motion by using coefficients appearing in the second-order action of scalar perturbations. We also derive conditions for the absence of ghost and Laplacian instabilities of tensor and vector perturbations and show that the existence of matter does not substantially modify the stabilities of dynamical degrees of freedom in the small-scale limit. On the other hand, the sound speed of scalar perturbations is affected by the presence of matter. Employing the quasi-static approximation for scalar perturbations deep inside the sound horizon, we derive analytic expressions of Newtonian and weak lensing gravitational potentials as well as two scalar perturbations arising from the scalar and vector fields. We apply our general framework to dark energy theories with the tensor propagation speed equivalent to the speed of light and show that the observables associated with the growth of matter perturbations and weak lensing potentials are generally affected by intrinsic vector modes and by interactions between scalar and vector fields.

New scaling solutions in cubic Horndeski theories

We propose a viable dark energy scenario in the presence of cubic Horndeski interactions and a standard scalar-field kinetic term with two exponential potentials. We show the existence of new scaling solutions along which the cubic coupling $G_3$ provides an important contribution to the field density that scales in the same way as the background fluid density. The solutions finally exit to the epoch of cosmic acceleration driven by a scalar-field dominated fixed point arising from the second exponential potential. We clarify the viable parameter space in which all the theoretically consistent conditions including those for the absence of ghost and Laplacian instabilities are satisfied on scaling and scalar-field dominated critical points. In comparison to Quintessence with the same scalar potential, we find that the cubic coupling gives rise to some novel features: (i) the allowed model parameter space is wider in that a steeper potential can drive the cosmic acceleration; (ii) the dark energy equation of state $w_{\phi}$ today can be closer to $-1$ relative to Quintessence; (iii) even if the density associated with the cubic coupling dominates over the standard field density in the scaling era, the former contribution tends to be suppressed at low redshifts. We also compute quantities associated with the growth of matter perturbations and weak lensing potentials under the quasi-static approximation in the sub-horizon limit and show that the cubic coupling leads to the modified evolution of perturbations which can be distinguished from Quintessence.

Finsler–Randers cosmology: dynamical analysis and growth of matter perturbations

We study for the first time the dynamical properties and the growth index of linear matter perturbations of the Finsler–Randers (FR) cosmological model, for which we consider that the cosmic fluid contains matter, radiation and a scalar field. Initially, for various FR scenarios we implement a critical point analysis and we find solutions which provide cosmic acceleration and under certain circumstances we can have de Sitter points as stable late-time attractors. Then we derive the growth index of matter fluctuations in various Finsler–Randers cosmologies. Considering cold dark matter and neglecting the scalar field component from the perturbation analysis we find that the asymptotic value of the growth index is , which is close to that of the concordance Λ cosmology, . In this context, we show that the current FR model provides the same Hubble expansion with that of the Dvali, Gabadadze and Porrati (DGP) gravity model. However, the two models can be distinguished at the perturbation level since the growth index of the FR model is ∼18.2% lower than that of the the DPG gravity . If we allow pressure in the matter fluid then we obtain , where is the matter equation of state parameter. Finally, we extend the growth index analysis by using the scalar field and we find that the evolution of the growth index in FR cosmologies is affected by the presence of scalar field.

Testing Einstein’s gravity and dark energy with growth of matter perturbations: Indications for new physics?

The growth index of matter fluctuations is computed for ten distinct accelerating cosmological models and confronted to the latest growth rate data via a two-step process. First, we implement a joint statistical analysis in order to place constraints on the free parameters of all models using solely background data. Second, using the observed growth rate of clustering from various galaxy surveys we test the performance of the current cosmological models at the perturbation level while either marginalizing over $\sigma_8$ or having it as a free parameter. As a result, we find that at a statistical level, i.e. after considering the best-fit $\chi^2$ or the value of the Akaike information criterion, most models are in very good agreement with the growth rate data and are practically indistinguishable from $\Lambda$CDM. However, when we also consider the internal consistency of the models by comparing the theoretically predicted values of $(\gamma_0, \gamma_1)$, i.e. the value of the growth index $\gamma(z)$ and its derivative today, with the best-fit ones, we find that the predictions of three out of ten dark energy models are in mild tension with the best-fit ones when $\sigma_8$ is marginalized over. When $\sigma_8$ is free we find that most models are not only in mild tension, but also predict low values for $\sigma_8$. This could be attributed to either a systematic problem with the growth-rate data or the emergence of new physics at low redshifts, with the latter possibly being related to the well-known issue of the lack of power at small scales. Finally, by utilizing mock data based on an LSST-like survey we show that with future surveys and by using the growth index parameterization, it will be possible to resolve the issue of the low $\sigma_8$ but also the tension between the fitted and theoretically predicted values of $(\gamma_0, \gamma_1)$.

Growth of matter perturbations in clustered holographic dark energy cosmologies

We investigate the growth of matter fluctuations in holographic dark energy cosmologies. First we use an overall statistical analysis involving the latest observational data in order to place constraints on the cosmological parameters. Then we test the range of validity of the holographic dark energy models at the perturbation level and its variants from the concordance $\Lambda$ cosmology. Specifically, we provide a new analytical approach in order to derive, for the first time, the growth index of matter perturbations. Considering a homogeneous holographic dark energy we find that the growth index is $\gamma \approx \frac{4}{7}$ which is somewhat larger ($\sim 4.8\%$) than that of the usual $\Lambda$ cosmology, $\gamma^{(\Lambda)}\approx \frac{6}{11}$. Finally, if we allow clustering in the holographic dark energy models then the asymptotic value of the growth index is given in terms of the effective sound speed $c_{\rm eff}^2$, namely $\gamma \approx \frac{3(1-c_{\rm eff}^2)}{7}$.

Cosmological constraints and cosmic growth factor for ghost dark energy models in varying G $G$ theories

The Ghost Dark Energy (GDE) model in varying Newton’s gravitational coupling (VG) theories is investigated. We first obtain the cosmological parameters of the model in modified FRW cosmology with varying $G$ and then study the growth of matter perturbations in this formalism. Applying a Markov Chain Monte Carlo (MCMC) simulation and using the recent observational data, including Baryonic Acoustic Oscillation (BAO), the cluster X-ray Gas Mass Fraction (XGMF), Cosmic Microwave Background radiation (CMB), Growth Function for matter perturbation (GF), type Ia supernova (SNIa) and Hubble data, constraint results on GDE model parameters in VG theory are: $\varOmega_{0m}=0.2751^{+0.0104+0.0208}_{-0.0104-0.0195}$ , $\varOmega_{0d}=0.7093^{+0.0123+0.0229}_{-0.0128-0.0245}$ , $\beta=-0.0156^{+0.0041+0.0082}_{-0.0042-0.0078}$ and $H_{0}=67.444^{+0.899+1.757}_{-0.873-1.829}$ . The results for concordance $\varLambda \mathrm{CDM}$ model are: $\varOmega_{0m}=0.2762^{+0.0097+0.0196}_{-0.0099-0.0188}$ , $\varOmega_{0d}=0.7238^{+0.0099+0.0188}_{-0.0097-0.0196}$ , and $H_{0}=70.265^{+0.797+1.575}_{-0.797-1.515}$ . We show that in this model the universe begins to accelerate at redshift $z_{t}\simeq0.4$ consistently in $1\sigma$ level with observations. It shows that the growth rate of this model is well fitted by observational growth data as the $\varLambda \mathrm{CDM}$ model.

Cosmic expansion and structure formation in running vacuum cosmologies

We investigate the dynamics of the Friedmann–Lemaître–Robertson–Walker (FLRW) flat cosmological models in which the vacuum energy varies with redshift. A particularly well-motivated model of this type is the so-called quantum field vacuum, in which both kind of terms [Formula: see text] and constant appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions at the background and perturbation levels. Specifically, it turns out that the functional form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution which could be observed nowadays and appears as dynamical DE. Interestingly, the low-energy behavior is very close to the usual Lambda cold dark matter (ΛCDM) model, but it is by no means identical. Finally, within the framework of the quantum field vacuum we generalize the large scale structure properties, namely growth of matter perturbations, cluster number counts and spherical collapse model.

Can modified gravity models reconcile the tension between the CMB anisotropy and lensing maps in Planck-like observations?

Planck-2015 data seem to favor a large value of the lensing amplitude parameter, ${A}_{\mathrm{L}}=1.22\ifmmode\pm\else\textpm\fi{}0.10$, in CMB spectra. This result is in $2\ensuremath{\sigma}$ tension with the lensing reconstruction result, ${A}_{\mathrm{L}}^{\ensuremath{\phi}\ensuremath{\phi}}=0.95\ifmmode\pm\else\textpm\fi{}0.04$. In this paper, we simulate several CMB anisotropy and CMB lensing spectra based on Planck-2015 best-fit cosmological parameter values and Planck bluebook beam and noise specifications. We analyze several modified gravity models within the effective field theory framework against these simulations and find that models whose effective Newton constant is enhanced can modulate the CMB anisotropy spectra in a way similar to that of the ${A}_{\mathrm{L}}$ parameter. However, in order to lens the CMB anisotropies sufficiently, like in the Planck-2015 results, the growth of matter perturbations is substantially enhanced and gives a high ${\ensuremath{\sigma}}_{8}$ value. This in turn proves to be problematic when combining CMB anisotropy data from Planck with other data, such as weak lensing from CFHTLenS which favor a smaller amplitude of matter fluctuations.

Effects of modified gravity onB-mode polarization

We explore the impact of modified gravity on B-modes, identifying two main separate effects: lensing and propagation of tensor modes. The location of the inflationary peak of the BB spectrum depends on the speed of gravitational waves; the amplitude of the lensing contribution depends on the anisotropic stress. We single out these effects using the quasi-static regime and considering models for which the background and the growth of matter perturbations are standard. Using available data we obtain that the gravitational wave speed is compatible with the speed of light and constrained to within about 10%.

Constraints on modified gravity from the Atacama Cosmology Telescope and the South Pole Telescope

The Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) have recently provided new and precise measurements of the Cosmic Microwave Background anisotropy damping tail. This region of the CMB angular spectra, thanks to the angular distortions produced by gravitational lensing, can probe the growth of matter perturbations and provide a test for general relativity. Here we make use of the ACT and SPT power spectrum measurements (combined with the recent WMAP9 data) to constrain f(R) gravity theories. Adopting a parametrized approach, we obtain an upper limit on the lengthscale of the theory of B_0 < 0.86 at 95% c.l. from ACT, while we get a significantly stronger bound from SPT with B_0 < 0.14 at 95% c.l..