Growth Of Large-scale Structure Research Articles

A crucial test of the phantom closed cosmological model

ABSTRACT We suggest a crucial direct-observational test for measuring distinction between the standard ΛCDM model and recently proposed phantom dark energy positive curvature cosmological model. The test is based on the fundamental distance–flux–redshift relation for general Friedmann models. It does not depend on the CMBR data, on the large-scale structure growth models, and also on the value of the Hubble constant H0. Our crucial test can be performed by future gamma-ray burst observations with THESEUS space mission and by using gravitational-wave standard siren observations with modern advanced LIGO–Virgo and also forthcoming LISA detectors.

Numerical Investigation on Aero-optical Reduction for Supersonic Turbulent Mixing Layer

The tangential injection flow commingled with the mainstream could be abstracted as mixing layer, and profound importance is attached to aero-optical reduction for film-cooling target-seeking vehicles in engineering application. Leveraging the in-house code based on explicit fifth-order Weighted Compact Nonlinear Scheme and ray-tracing method, the supersonic mixing layer is numerically simulated to investigate the effect of inflow disturbance on large-scale structure growth and aero-optical reduction. The vortex growth would be stimulated somewhere when the frequency of inflow perturbation added is close to the local characteristic most unstable value. Based on such cognition, different techniques of super-harmonic and sub-harmonic disturbance are employed for effective aero-optical suppression schemes in the following research. The sub-harmonic one without phase shift shows such ability in the whole turbulent region, and additional perturbation of white noise is also promising for better control consequence.

Growth of non-linear structures and spherical collapse in the Galileon Ghost Condensate model

We present a detailed study of the collapse of a spherical matter overdensity and the non-linear growth of large scale structures in the Galileon ghost condensate (GGC) model. This model is an extension of the cubic covariant Galileon (G3) which includes a field derivative of type $(\nabla_\mu\phi\nabla^\mu\phi)^2$ in the Lagrangian. We find that the cubic term activates the modifications in the main physical quantities whose time evolution is then strongly affected by the additional term. Indeed, the GGC model shows largely mitigated effects in the linearised critical density contrast, non-linear effective gravitational coupling and the virial overdensity with respect to G3 but still preserves peculiar features with respect to the standard $\Lambda$CDM cosmological model, e.g. both the linear critical density contrast and the virial overdensity are larger than those in $\Lambda$CDM. The results of the spherical collapse model are then used to predict the evolution of the halo mass function, non-linear matter and lensing power spectra. While at low masses the GGC model presents about 10% fewer objects with respect to $\Lambda$CDM, at higher masses for $z>0$ it predicts 10% ($z=0.5$)-20% ($z=1$) more objects per comoving volume. Using a phenomenological approach to include the screening effect in the matter power spectrum, we show that the difference induced by the modifications of gravity are strongly dependent on the screening scale and that differences can be up to 20% with respect to $\Lambda$CDM. These differences translate to the lensing power spectrum where qualitatively the largest differences with respect to the standard cosmological model are for $\ell<10^3$. Depending on the screening scale, they can be up to 25% on larger angular scales and then decrease for growing $\ell$. These results are obtained for the best fit parameters from linear cosmological data for each model.

Endowing Λ with a dynamic nature: Constraints in a spatially curved universe

In this study, we consider three dark energy models in which $\Lambda$ is not constant, but has a dynamic nature that depends on the Hubble parameter $H$ and/or its time derivative $\dot{H}$. We analyze the generalized running vacuum model, for which $\Lambda(H)=A+BH^2+C\dot{H}$, along with the two models obtained by setting $B$ or $C$ equal to zero. A null value for $C$ yields the classical running vacuum model (RVM), while $B=0$ corresponds to what we term the generalized running vacuum sub-case, or GRVS. Our main aim is to investigate whether these models can accommodate non-zero spatial curvature. To this end, we carry out a Markov Chain Monte Carlo analysis using data for the observables associated with Type-Ia supernovae, cosmic chronometers, the cosmic microwave background and baryon acoustic oscillations, as well as two values for the Hubble constant. Then we include data relating to the growth of large-scale structure (LSS) and repeat the procedure. Our results indicate that taking LSS observations into account helps to tighten constraints and determine a definite sign for the model parameters. In the case of the RVM and GRVS, the addition of growth data results in dynamical vacuum energy being preferred to a cosmological constant at a little over $1\sigma$. This happens in both the flat and non-flat scenarios -- there are only a few exceptions -- but comes at the cost of an extra parameter which can degrade the performance of the models (as assessed by model selection criteria). Of special relevance is the fact that the inclusion of LSS data appears to increase compatibility with a flat geometry. It also brings the constraints on the Hubble constant closer to the range of values established by \emph{Planck}.

Consistent modeling of velocity statistics and redshift-space distortions in one-loop perturbation theory

The peculiar velocities of biased tracers of the cosmic density field contain important information about the growth of large scale structure and generate anisotropy in the observed clustering of galaxies. Using N-body data, we show that velocity expansions for halo redshift-space power spectra are converged at the percent-level at perturbative scales for most line-of-sight angles μ when the first three pairwise velocity moments are included, and that the third moment is well-approximated by a counterterm-like contribution. We compute these pairwise-velocity statistics in Fourier space using both Eulerian and Lagrangian one-loop perturbation theory using a cubic bias scheme and a complete set of counterterms and stochastic contributions. We compare the models and show that our models fit both real-space velocity statistics and redshift-space power spectra for both halos and a mock sample of galaxies at sub-percent level on perturbative scales using consistent sets of parameters, making them appealing choices for the upcoming era of spectroscopic, peculiar-velocity and kSZ surveys.

Scaling solutions and weak gravity in dark energy with energy and momentum couplings

We argue that the ΛCDM tensions of the Hubble-Lemaȋtre expansion rate H0 and the clustering normalization σ8 can be eased, at least in principle, by considering an interaction between dark energy and dark matter in such a way to induce a small and positive early effective equation of state and a weaker gravity. For a dark energy scalar field ϕ interacting with dark matter through an exchange of both energy and momentum, we derive a general form of the Lagrangian allowing for the presence of scaling solutions. In a subclass of such interacting theories, we show the existence of a scaling ϕ-matter-dominated-era (ϕMDE) which can potentially alleviate the H0 tension by generating an effective high-redshift equation of state. We also study the evolution of perturbations for a model with ϕMDE followed by cosmic acceleration and find that the effective gravitational coupling relevant to the linear growth of large-scale structures can be smaller than the Newton gravitational constant G at low redshifts. The momentum exchange between dark energy and dark matter plays a crucial role for realizing weak gravity, while the energy transfer is also required for the existence of ϕMDE.

Weak cosmic growth in coupled dark energy with a Lagrangian formulation

We investigate a dark energy scenario in which a canonical scalar field ϕ is coupled to the four velocity ucμ of cold dark matter (CDM) through a derivative interaction ucμ∂μϕ. The coupling is described by an interacting Lagrangian f(X,Z), where f depends on X=−∂μϕ∂μϕ/2 and Z=ucμ∂μϕ. We derive stability conditions of linear scalar perturbations for the wavelength deep inside the Hubble radius and show that the effective CDM sound speed is close to 0 as in the standard uncoupled case, while the scalar-field propagation speed is affected by the interacting term f. Under a quasi-static approximation, we also obtain a general expression of the effective gravitational coupling felt by the CDM perturbation. We study the late-time cosmological dynamics for the coupling f∝X(2−m)/2Zm and show that the gravitational coupling weaker than the Newton constant can be naturally realized for m>0 on scales relevant to the growth of large-scale structures. This allows the possibility for alleviating the tension of σ8 between low- and high-redshift measurements.

Scalar-field dark energy nonminimally and kinetically coupled to dark matter

We provide a general framework for studying the dark energy cosmology in which a scalar field $\phi$ is nonminimally and kinetically coupled to Cold Dark Matter (CDM). The scalar-graviton sector is described by the action of Horndeski theories with the speed of gravitational waves equivalent to that of light, whereas CDM is treated as a perfect fluid given by a Schutz-Sorkin action. We consider two interacting Lagrangians of the forms $f_1(\phi,X)\rho_c (n_c)$ and $f_2 (n_c, \phi,X) J_c^{\mu} \partial_{\mu}\phi$, where $X=-\partial^{\mu} \phi \partial_{\mu} \phi/2$, $\rho_c$ and $n_c$ are the energy density and number density of CDM respectively, and $J_c^{\mu}$ is a vector field related to the CDM four velocity. We derive the scalar perturbation equations of motion without choosing any special gauges and identify conditions for the absence of ghosts and Laplacian instabilities on scales deep inside the sound horizon. Applying a quasi-static approximation in a gauge-invariant manner, we also obtain the effective gravitational couplings felt by CDM and baryons for the modes relevant to the linear growth of large-scale structures. In particular, the $n_c$ dependence in the coupling $f_2$ gives rise to an interesting possibility for realizing the gravitational coupling with CDM weaker than the Newton gravitational constant $G$.

Constraints on the growth rate using the observed galaxy power spectrum

The large-scale structure growth index γ provides a consistency test of the standard cosmology and is a potential indicator of modified gravity. We investigate the constraints on γ from next-generation spectroscopic surveys, using the power spectrum that is observed in redshift space, i.e., the angular power spectrum. The angular power spectrum avoids the need for an Alcock-Packzynski correction. It also naturally incorporates cosmic evolution and wide-angle effects, without any approximation. We include the cross-correlations between redshift bins, using a hybrid approximation when the total number of bins is computationally unfeasible. We show that the signal-to-noise on γ increases as the redshift bin-width is decreased. Shot noise per bin also increases—but this is compensated by the increased number of auto- and cross-spectra. In our forecasts, we marginalise over the amplitude of primordial fluctuations and other standard cosmological parameters, including the dark energy equation of state parameter, as well as the clustering bias. Neglecting cross-bin correlations increases the errors by ∼40–150%. Using only linear scales, we find that a DESI-like BGS survey and an HI intensity mapping survey with the SKA1 precursor MeerKAT deliver similar errors of ∼4–6%, while a Euclid-like survey and an SKA1 intensity mapping survey give ∼3% errors.

How complex is the cosmic web?

ABSTRACT The growth of large-scale cosmic structure is a beautiful exemplification of how complexity can emerge in our Universe, starting from simple initial conditions and simple physical laws. Using enzo cosmological numerical simulations, I applied tools from Information Theory (namely, ‘statistical complexity’) to quantify the amount of complexity in the simulated cosmic volume, as a function of cosmic epoch and environment. This analysis can quantify how much difficult to predict, at least in a statistical sense, is the evolution of the thermal, kinetic, and magnetic energy of the dominant component of ordinary matter in the Universe (the intragalactic medium plasma). The most complex environment in the simulated cosmic web is generally found to be the periphery of large-scale structures (e.g. galaxy clusters and filaments), where the complexity is on average ∼10–102 times larger than in more rarefied regions, even if the latter dominate the volume-integrated complexity of the simulated Universe. If the energy evolution of gas in the cosmic web is measured on a ≈100 ${\rm kpc}\, h^{-1}$ resolution and over a ≈200 $\rm Myr$ time-scale, its total complexity is in the range of $\sim 10^{16}\!-\!10^{17} \rm \,bits$, with little dependence on the assumed gas physics, cosmology, or cosmic variance.

CMB lensing reconstruction biases in cross-correlation with large-scale structure probes

The cross-correlation between cosmic microwave background (CMB) gravitational lensing and large-scale structure tracers will be an important cosmological probe in the coming years. Quadratic estimators provide a simple and powerful (if suboptimal) way to reconstruct the CMB lensing potential and are widely used. For Gaussian fields, the cross-correlation of a quadratic-estimator CMB lensing reconstruction with a tracer is exactly unbiased if the power spectra are known and consistent analytic lensing mode response functions are used. However, the bispectrum induced by non-linear large-scale structure growth and post-Born lensing can introduce an additional bias term (NL(3/2)) in the cross-correlation spectrum, similar to the NL(3/2) bias in the auto-spectrum demonstrated in recent works. We give analytic flat-sky results for the cross-correlation bias using approximate models for the post-Born and large-scale structure cross-bispectra, and compare with N-body simulation results using ray-tracing techniques. We show that the bias can be at the 5–15% level in all large-scale structure cross-correlations using small-scale CMB temperature lensing reconstruction, but is substantially reduced using polarization-based lensing estimators or simple foreground-projected temperature estimators. The relative magnitude of these effects is almost three times higher than in the CMB lensing auto-correlation, but is small enough that it can be modelled to sufficient precision using simple analytic models. We show that NL(3/2) effects in cross-correlation will be detected with high significance when using data of future surveys and could affect systematic effects marginalization in cosmic shear measurements mimicking galaxy intrinsic alignment.

Investigating the degeneracy between modified gravity and massive neutrinos with redshift-space distortions

There is a well known degeneracy between the enhancement of the growth of large-scale structure produced by modified gravity models and the suppression due to the free-streaming of massive neutrinos at late times. This makes the matter power-spectrum alone a poor probe to distinguish between modified gravity and the concordance ΛCDM model when neutrino masses are not strongly constrained. In this work, we investigate the potential of using redshift-space distortions (RSD) to break this degeneracy when the modification to gravity is scale-dependent in the form of Hu-Sawicki f(R). We find that if the linear growth rate can be recovered from the RSD signal, the degeneracy can be broken at the level of the dark matter field. However, this requires accurate modelling of the non-linearities in the RSD signal, and we here present an extension of the standard perturbation theory based model for non-linear RSD that includes both Hu-Sawicki f(R) modified gravity and massive neutrinos.

Probing redshift-space distortions with phase correlations

Redshift-space distortions are a sensitive probe of the growth of large-scale structure. In the linear regime, redshift-space distortions are fully described by the multipoles of the two-point correlation function. In the nonlinear regime, however, higher-order statistics are needed to capture the full information of the galaxy density field. In this paper, we show that the redshift-space line correlation function--which is a measure of Fourier phase correlations--is sensitive to the nonlinear growth of the density and velocity fields and to the nonlinear mapping between real and redshift space. We expand the line correlation function in multipoles, and we show that almost all of the information is encoded in the monopole, quadrupole, and hexadecapole. We argue that these multipoles are highly complementary to the multipoles of the two-point correlation function: first, because they are directly sensitive to the difference between the density and the velocity coupling kernels, which is a purely nonlinear quantity; and second, because the multipoles are proportional to different combinations of $f$ and $\sigma_8$. Measured in conjunction with the two-point correlation function and the bispectrum, the multipoles of the line correlation function could therefore allow us to disentangle efficiently these two quantities and to test modified theories of gravity.

Structure formation in dark energy cosmologies described by PADE parametrization

We study the imprints on the formation of cosmic structures of a particular class of dark energy parameterizations dubbed PADE parameterization. Here we investigate how dark energy can affect the growth of large scale structures of the universe in framework of spherical collapse model. The dynamics of the spherical collapse of a dark matter halo depends on the properties of the dark energy model. We show that the properties of spherical collapse scenario are directly affected by the evolution of dark energy. We obtain the main parameters of spherical collapse for two different DE parameterizations in two different approaches: first the homogeneous DE approach, in which dark energy does not exhibit fluctuations on cluster scales and the other, clustered DE scenario in which, dark energy components inside the overdense region collapses similar to dark matter. Using the Sheth-Tormen mass function, we investigate the abundance of virialized halos in the framework of PADE parameterizations. Specifically, the present analysis shows that the number count of dark matter halos depends on the evolution of DE parameterizations and clustering properties of dark energy. Also we show that perturbations in phantom DE components enhance the growth of matter perturbations. This result were obtained in the literature for dark energy parameterizations that are phantom at all redshifts. But we obtained same results for dark energy parameterizations which are in phantom regime and enter in quintessence region at relatively low redshifts. We also show that in parameterizations under study, low mass halos were formed before massive halos.

End of cosmic growth

The growth of large scale structure is a battle between gravitational attraction and cosmic acceleration. We investigate the future behavior of cosmic growth under both general relativity (GR) and modified gravity during prolonged acceleration, deriving analytic asymptotic behaviors and showing that gravity generally loses and growth ends. We also note the `why now' problem is equally striking when viewed in terms of the shut down of growth. For many models inside GR the gravitational growth index $\gamma$ also shows today as a unique time between constant behavior in the past and a higher asymptotic value in the future. Interestingly, while $f(R)$ models depart in this respect dramatically from GR today and in the recent past, their growth indices are identical in the asymptotic future and past.

Self-gravitating Λ-media

We address the question whether a medium featuring p+ρ =0, dubbed Λ-medium, has to be necessarily a cosmological constant. By using effective field theory, we show that this is not the case for a class of media comprising perfect fluids, solids and special super solids, providing an explicit construction. The low energy excitations are non trivial and lensing, the growth of large scale structures can be used to clearly distinguish Λ-media from a cosmological constant.

Suppression of Cavity Flow Oscillations via Three-Dimensional Steady Blowing

This paper presents an investigation of the flow physics and control of cavity flow oscillations using a three-dimensional (3-D) array of steady jets located near the cavity leading edge. The array injects 3-D, steady flow normal to the freestream to suppress the fluctuating surface pressure in a rectangular cavity with a length-to-depth ratio of 6 for Mach 0.3 to 0.7. Sixteen configurations are assessed for their suppression as a function of the aggregate momentum coefficient , spatial duty cycle , and dimensionless wavelength . Significant reductions of fluctuating surface pressure are observed. Schlieren and particle image velocimetry are performed to investigate the baseline and controlled flows. Companion large-eddy simulations with spanwise periodic boundary conditions at Mach 0.6 generally agree with the experiments, despite a significant difference in the Reynolds numbers. The simulations show that control reduces the pressure fluctuations inside the entire cavity, albeit at a higher level of . Spanwise wavelike structures produced by the control input distort the shear layer, inhibit the growth of large-scale vortical structures, and reduce the strength and length scale of turbulent fluctuations near the impingement region. A slot-configuration design guide is provided, which compares favorably with the limited available data in the literature.

Lensing reconstruction in post-Born cosmic microwave background weak lensing

The study of the Cosmic Microwave Background (CMB) lensing potential has established itself by now as a robust way of probing the physics of large-scale structure growth. The most common estimators of the lensing potential are derived under the assumption of Gaussianity of the matter distribution and in the Born approximation of the photon diffusion. In this paper we study the performance of quadratic estimators when applied to realistic sky maps extracted from multiple-lens ray tracing techniques in cosmological $N$-body simulations. These are expected to model accurately the effects due to the non-Gaussianity of the matter distribution induced by its nonlinearity and the deviation from the Born approximation. We show that both these effects on their own lead to reconstruction biases, but these tend to partially cancel each other when both these effects are considered together. We forecast the impact of these biases on the estimation of cosmological parameters for future high-sensitivity CMB experiments like CMB-S4. We find that the cold dark matter density, $\Omega_\textrm{cdm}$, the optical depth to reionization $\tau$, the amplitude of primordial inflationary perturbations, $A_s$ and the sum of neutrino masses, $M_\nu$, could be biased at the 1-2$\sigma$ level, if no external data set is used. We also observe a reduction of the bias if external data like baryon acoustic oscillations (BAO) is included.

Cluster-void degeneracy breaking: Modified gravity in the balance

Combining galaxy cluster and void abundances is a novel, powerful way to constrain deviations from General Relativity and the $\Lambda$CDM model. For a flat $w$CDM model with growth of large-scale structure parameterized by the redshift-dependent growth index $\gamma(z) = \gamma_0 + \gamma_1 z/(1+z)$ of linear matter perturbations, combining void and cluster abundances in future surveys with Euclid and the 4-metre Multi-Object Spectroscopic Telescope (4MOST) could improve the Figure of Merit for ($w, \gamma_0, \gamma_1$) by a factor of 20 compared to individual abundances. In an ideal case, improvement on current cosmological data is a Figure of Merit factor $600$ or more.

Large-scale structure phenomenology of viable Horndeski theories

Phenomenological functions $\Sigma$ and $\mu$, also known as $G_{\rm light}/G$ and $G_{\rm matter}/G$, are commonly used to parameterize modifications of the growth of large-scale structure in alternative theories of gravity. We study the values these functions can take in Horndeski theories, i.e. the class of scalar-tensor theories with second order equations of motion. We restrict our attention to models that are in a broad agreement with tests of gravity and the observed cosmic expansion history. In particular, we require the speed of gravity to be equal to the speed of light today, as required by the recent detection of gravitational waves and electromagnetic emission from a binary neutron star merger. We examine the correlations between the values of $\Sigma$ and $\mu$ analytically within the quasi-static approximation, and numerically, by sampling the space of allowed solutions. We confirm that the conjecture made in [Pogosian:2016pwr], that $(\Sigma-1)(\mu -1) \ge 0$ in viable Horndeski theories, holds very well. Along with that, we check the validity of the quasi-static approximation within different corners of Horndeski theory. Our results show that, even with the tight bound on the present day speed of gravitational waves, there is room within Horndeski theories for non-trivial signatures of modified gravity at the level of linear perturbations.