First-Order Cosmological Perturbations Engendered by Point-Like Masses

2017

ApJ

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In the ΛCDM framework, presenting nonrelativistic matter inhomogeneities as discrete massive particles, we develop the second-order cosmological perturbation theory. Our approach relies on the weak gravitational field limit. The derived equations for the second-order scalar, vector and tensor metric corrections are suitable at arbitrary distances including regions with nonlinear contrasts of the matter density. We thoroughly verify fulfilment of all Einstein equations as well as self-consistency of order assignments. In addition, we achieve logical positive results in the Minkowski background limit. Feasible investigations of the cosmological backreaction manifestations by means of relativistic simulations are also outlined.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Second-order Cosmological Perturbations Engendered by Point-like Masses

Brilenkov

2017

ApJ

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Perfect fluids withω=constas sources of scalar cosmological perturbations

Physics of the Dark Universe

Brilenkov

2017

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We make a generalization of a self-consistent first-order perturbation scheme, being suitable for all (sub-horizon and super-horizon) scales, which has been recently constructed for the concordance cosmological model and discrete presentation of matter sources, to the case of extended models with extra perfect fluids and continuous presentation. Namely, we derive a single equation determining the scalar perturbation and covering the whole space as well as define the corresponding universal Yukawa interaction range. We also demonstrate explicitly that the structure growth is suppressed at distances exceeding this fundamental range.

Analytic expressions for the second-order scalar perturbations in theΛCDM Universe within the cosmic screening approach

Physics of the Dark Universe

Guran

Zhuk

2019

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We study the second-order scalar perturbations in the conventional ΛCDM Universe within the cosmic screening approach. The analytic expressions for both the velocity-independent and velocity-dependent second-order scalar perturbations are derived. We demonstrate how the Yukawa screening effect, which is inherent in the first-order metric corrections, manifests itself in the second-order ones. It is shown that the obtained formulas for the second-order perturbations are reduced to the known post-Newtonian expressions at distances much smaller than the Yukawa screening length. In the era of precision cosmology, these analytic formulas play an important role since the second-order metric corrections may affect the interpretation of observational data (e.g., the luminosity-redshift relation, gravitational lensing, baryon acoustic oscillations). IntroductionAccording to the cosmological principle [1, 2], our Universe is isotropic and homogeneous at large enough scales. This follows from the natural assumption that the laws of physics should be the same wherever in the Universe we are. Starting from a certain scale, the distribution of inhomogeneities (e.g., galaxies and groups of galaxies) should be statistically homogeneous. As a result, such statistically homogeneous Universe has the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, and its dynamics is described by the Friedmann equations. This is the zero-order/background approach. Obviously, inhomogeneities disturb this background resulting in first-and higher-order perturbations. They play a crucial role in the investigation of the large scale structure formation. Evidently (by definition!), the average values of the first-order perturbations should be equal to zero (see, e.g., [3]). On the other hand, the average values of the second-order perturbations are different from zero and can affect the background spacetime and matter. This effect is called backreaction (see, e.g., [4,5,6,7,8,9] and references therein). It is important to determine how strong the backreaction is and to what extent we may use the standard FLRW metric as a background one. As an example, the backreaction may affect the baryon acoustic oscillations [5,10]. The second-order perturbations also contribute to the luminosity-redshift relation [11] and gravitational lensing [12,13].Within the cosmic screening approach, the theory of the first-order perturbations was developed in the papers [14,15,16,17,18]. In its framework, inhomogeneities in the Universe (e.g., galaxies and their groups) are considered as point-like gravitating masses. These masses disturb the background spacetime and matter. For example, the energy density fluctuation reads δε ≈ (c 2 /a 3 )δρ + (3ρc 2 /a 3 )Φ, where c denotes the speed of light, a is the scale factor of the Universe, and we singled out the gravitational potential Φ. Consequently, the