Effect of the Modified Gravity on the Large-scale Structure Formation

Structure formation in dark matter particle production cosmology

We consider the linear growth of matter perturbations on low redshifts in some f(R) dark energy (DE) models. We discuss the definition of dark energy (DE) in these models and show the differences with scalar-tensor DE models. For the f(R) model recently proposed by Starobinsky we show that the growth parameter γ0≡γ(z = 0) takes the value γ0 ≃ 0.4 for Ωm,0 = 0.32 and γ0 ≃ 0.43 for Ωm,0 = 0.23, allowing for a clear distinction from ΛCDM. Though a scale-dependence appears in the growth of perturbations on higher redshifts, we find no dispersion for γ(z) on low redshifts up to z ∼ 0.3, γ(z) is also quasi-linear in this interval. At redshift z = 0.5, the dispersion is still small with Δγ ≃ 0.01.As for some scalar-tensor models, we find here too a large value for γ′0≡(dγ/dz)(z = 0), γ′0 ≃ −0.25 for Ωm,0 = 0.32 and γ′0 ≃ −0.18 for Ωm,0 = 0.23. These values are largely outside the range found for DE models in General Relativity (GR). This clear signature provides a powerful constraint on these models.

A dependence of the neutrino masses on the dark energy scalar field could provide a solution to the why now problem of dark energy. The dynamics of the resulting cosmological model---growing neutrino quintessence---include an attractive force between neutrinos substantially stronger than gravity. We present a comprehensive approach towards an understanding of the full cosmological evolution, including the formation of large-scale neutrino structures. Important effects we account for are local variations in the dark energy and the backreaction on the background evolution, as well as relativistic neutrino velocities. For this aim, we develop a relativistic $N$-body treatment of the neutrinos combined with an explicit computation of the local quintessence field. At its current stage, the simulation method is successful until $z\ensuremath{\approx}1$ and reveals a rich phenomenology. We obtain a detailed picture of the formation of large-scale neutrino structures and their influence on the evolution of matter, dark energy, and the late-time expansion of the Universe.

It seems that the galaxy formation theory is now confusing. In order to resolve this situation the theoretical framework on the formation of large-scale structure in the Universe is reviewed, especially paying attention to the first-ranked observational facts. Then, the conditions which the theory must satisfy with minimum parameters are summarized in relation to additional observational facts. Finally, a possible framework of the galaxy formation theory which looks well consistent with the large-scale structure is presented.

The formation of cosmic structure results from the action of gravity on matter in an expanding Universe. As the evolution proceeds, the velocity field changes from being single-valued almost everywhere in space to being multi-valued over a complex web of ‘multistreaming’ regions associated with the formation of large-scale structure (LSS) such as halos (or clumps), filaments, and sheets. Until recently, these structures have been investigated primarily via the (scalar) mass density field. In this application paper we apply data analysis and visualization techniques to cosmological simulations with the aim of studying multistreaming regions using velocity-based probes. Compared to the current practice of using density information (e.g., morphology estimators, locating overdense regions with halo finders), we show that velocity-based methods can provide useful supporting, as well as complementary, information. Because the density field and multistreaming are correlated but do not contain the same information, new and interesting information about the properties of the large-scale structure may be extracted, e.g., capturing dynamical behavior not possible with density-based estimators. Incorporating a novel method for setting thresholds for the velocity-based estimators, we study the relationships between the density field as represented by compact overdense halos and the different properties of multistreaming regions as represented by different velocity-based estimators.

A primordial magnetic field (PMF) would be expected to manifest itself in the cosmic microwave background (CMB) temperature and polarization anisotropies, and also in the formation of large scale structure(LSS). In this article, we demonstrate how the PMF is an important cosmological physical process on small scales as follows, We also report the newest constraints on the PMF amplitude Bλ and the power spectral index nB which have been deduced from the available CMB observational data by using our computational framework and the Markov chain Monte Carlo method. In particular we find that |Bλ|<2.10(68%CL) nG and < 2.98(95%CL) nG and nB<−1.19(68%CL) and <−0.25(95%CL) at a present scale of 1 Mpc.

We study the growth of linear matter density perturbations in a modified gravity approach of scalar field couplings with metric and torsion. In the equivalent scalar-tensor formulation, the matter fields in the Einstein frame interact as usual with an effective dark energy component, whose dynamics are presumably governed by a scalar field that sources a torsion mode. As a consequence, the matter density ceases to be self-conserved, thereby making an impact not only on the background cosmological evolution but also on the perturbative spectrum of the local inhomogeneities. In order to estimate the effect on the growth of the linear matter perturbations, with the least possible alteration of the standard parametric form of the growth factor, we resort to a suitable Taylor expansion of the corresponding exponent, known as the growth index, about the value of the cosmic scale factor at the present epoch. In particular, we obtain an appropriate fitting formula for the growth index in terms of the coupling function and the matter density parameter. While the overall parametric formulation of the growth factor is found to fit well with the latest redshift-space-distortion (RSD) and the observational Hubble (OH) data at low redshifts, the fitting formula enables us to constrain the growth index to well within the concordant cosmological limits, thus ensuring the viability of the formalism.

It is known than the inclusion of spatial curvature can modify the evolution of matter perturbations and affect the Large Scale Structure (LSS) formation. We quantify the effects of the nonzero spatial curvature in terms of LSS formation for a cosmological model with a running vacuum energy density and a warm dark matter component. The evolution of density perturbations and the modified shape of their power spectrum are constructed and analyzed.

We report on X-ray observations of two galaxy clusters, Abell 1555 and Abell 1558, with Suzaku, which are included in a large-scale filamentary structure and a supercluster, to search for non-thermal emission driven by shocks produced during structure formation. These two clusters were detected by Suzaku/XIS for the first time in the X-ray band of 0.5–7 keV. No significant flux has been detected by HXD in the energy band of 13–40 keV, and upper limits are reported. From an analysis of the XIS data, we found that the spectrum of A 1555 could be fit by a thermal plus power-law model, significantly better than a single-temperature pure thermal spectrum. If this power-law component is due to inverse-Compton scattering, the fraction of the total baryon energy imparted to non-thermal electrons is consistent with the typical value inferred from observations of other clusters. However, other scenarios (e.g., underlying AGNs, multi-temperature thermal models) cannot be excluded, and further investigation of this system is desired. Basic physical properties of A 1555 (e.g., total mass) are also reported.

In magnetized electron-depleted multi-ion dusty plasmas, a possibility of self-organization is determined. Making use of the equation of motion of the plasma's mobile species, i.e., a positive ion and two types of negative ions with Ampère's law, we obtain a quadruple Beltrami field. This higher order Beltrami field is characterized by four scale parameters. We have investigated the generation of self-organized structures. The typical length of these structures is attributed to the skin depth λp of positive ions. The influence of Beltrami parameters and scale parameters on the structure formation has also been investigated. It is found that there is a possibility of the formation of large scale structures of the order of system size and the formation of small scale structures of the order of skin depth simultaneously in the electron depleted multi-ion dusty plasmas, which are very useful to explain the dynamo theory. This study should be useful to describe the relaxed structures in space plasmas such as the D-region of Earth's mesosphere and F-ring of Saturn and in laboratory work where the dust particles are present as impurities.

The inclusion of dissipative effects in cosmic fluids modifies their clustering properties and could have observable effects on the formation of large scale structures. We analyse the evolution of density perturbations of cold dark matter endowed with causal bulk viscosity. The perturbative analysis is carried out in the Newtonian approximation and the bulk viscosity is described by the causal Israel-Stewart (IS) theory. In contrast to the non-causal Eckart theory, we obtain a third order evolution equation for the density contrast that depends on three free parameters. For certain parameter values, the density contrast and growth factor in IS mimic their behaviour in $\Lambda$CDM when $z \geq 1$. Interestingly, and contrary to intuition, certain sets of parameters lead to an increase of the clustering.

We consider a class of models for the formation of large scale structure, in which each void is generated by a single giant explosion. The voids must form at a redshift 15–25, for several independent reasons. 1) Gas which is shock heated to a temperature ∼ 5 · 107°K can cool sufficiently to fragment and form galaxies only when Compton cooling is efficient. 2) The local velocity field is too chaotic unless the peculiar velocities of the expanding shells of galaxies are damped in the Hubble flow to less than ∼ 150 km s−1. 3) The redistribution of baryons onto shells excites growing modes in the velocity field of wavelength comparable to the size of the voids. We require the RMS peculiar velocity to exceed ∼ 500 km s−1. 4) If the voids form too early, then dark matter interior to the shells catches up with the shells, and galaxies and dark matter are no longer segregated.

FORMATION OF LARGE SCALE STRUCTURES OF THE UNIVERSE ON THE CONNECTION MACHINE-2.

Do not be too proud of this technological terror you've constructed. The ability to simulate the formation of large scale structure is insignificant next&amp;nbsp;to the power of the Force.

With a new visualization technique, a strong suppression of small scale coherent structures (filaments) in turbulence is observed when a drag reducing polymer is added. Simultaneously, the rate of formation of large scale structures (eddies) out of these filaments decreases, which may be an important observation in the explanation of turbulent drag reduction.