Перегляд за Автор "Zhuk, Oleksandr I."
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Документ Cosmological perturbations in presence of scalar fields(Astroprint, 2014) Burgazli, A. Yu.; Eingorn, Maxim V.; Zhuk, Oleksandr I.We investigate the role of the scalar field assuming its presence at late stages of the Universe evolution together with dust presented by a system of an arbitrary number of gravitating masses (galaxies, groups of galaxies and clusters of galaxies) and the cosmological constant in the framework of the theory of scalar cosmological perturbations. In particular, we discuss the case of the homogeneous scalar field and its possible influence on the gravitational potentials representing metric perturbations. We also focus attention on the interconnection between the astrophysical problem and the cosmological one in the scalar field presence.Документ DARK SIDE OF QUARK BAG MODEL(Astroprint, 2013) Brilenkov, Maxim; Eingorn, Maxim V.; Jenkovszky, Laszlo; Zhuk, Oleksandr I.We calculate the present expansion of our Universe endowed with relict colored objects – quarks and gluons – that survived hadronization either as isolated islands of quark-gluon nuggets or spread uniformly in the Universe. The QNs can play the role of dark matter.Документ Different approaches for dark matter halos of clusters of galaxies(Astroprint, 2014) Brilenkov, R. D.; Eingorn, Maxim V.; Zhuk, Oleksandr I.To describe the density profile of dark matter halos of clusters of galaxies, we compare the approach based on the Schwarzschild-de Sitter metric with a recently developed mechanical one (discrete cosmology inside the cell of uniformity). In the first approach, the cosmological effects are completely incorporated into the cosmological constant, while in the second one the scale factor enters directly the corresponding equations. Hence, in the latter case we can take into account the effect on the density profiles not only the cosmological constant, but also other material components. Thus, we can evaluate how this dynamic impact is considerable and testable.Документ DYNAMICS OF COSMIC BODIES IN THE OPEN UNIVERSE(Astroprint, 2012) Kudinova, A. V.; Eingorn, Maxim V.; Zhuk, Oleksandr I.ABSTRACT. As it has been recently demonstrated,the mathematical model with the hyperbolic space(or, in other words, with the negative spatial curvature)is the most appropriate one for describing the inhomogeneous Universe at late stages of its evolution in the framework of the theory of scalar perturbations. In this model we develop a dynamic approach and investigate nonrelativistic motion of two, three and even more cosmic bodies against the cosmological background, perturbed locally by density inhomogeneities (namely, galaxies).Документ Effect of peculiar velocities on the gravitational potential in cosmological models with perfect fluids(2020) Burgazli, Alvina; Shulga, Valerii; Yükselci, A. Emrah; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWe consider a universe filled with perfect fluid with the constant equation of state parameter ω. In the theory of scalar perturbations, we study the effect of peculiar velocities on the gravitational potential. For radiation with ω=1/3, we obtain the expression for the gravitational potential in the integral form. Numerical calculation clearly demonstrates the modulation of the gravitational potential by acoustic oscillations due to the presence of peculiar velocities. We also show that peculiar velocities affect the gravitational potential in the case of the frustrated network of cosmic strings with ω=−1/3.Документ Effect of the Cubic Torus Topology on Cosmological Perturbations(2021) Eingorn, Maxim; Canay, Ezgi; Metcalf, Jacob M.; Brilenkov, Maksym; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWe study the effect of the cubic torus topology of the Universe on scalar cosmological perturbations which define the gravitational potential. We obtain three alternative forms of the solution for both the gravitational potential produced by point-like masses, and the corresponding force. The first solution includes the expansion of delta-functions into Fourier series, exploiting periodic boundary conditions. The second one is composed of summed solutions of the Helmholtz equation for the original mass and its images. Each of these summed solutions is the Yukawa potential. In the third formula, we express the Yukawa potentials via Ewald sums. We show that for the present Universe, both the bare summation of Yukawa potentials and the Yukawa-Ewald sums require smaller numbers of terms to yield the numerical values of the potential and the force up to desired accuracy. Nevertheless, the Yukawa formula is yet preferable owing to its much simpler structure.Документ Effect of the spatial curvature of the Universe on the form of the gravitational potential(2019) Eingorn, Maxim; Yükselci, A. Emrah; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWithin the cosmic screening approach, we obtain the exact formulas for the velocity-independent gravitational potentials produced by matter in the form of discrete sources distributed in the open and closed Universes. These formulas demonstrate that spatial curvature of the Universe considerably affect the form of the potentials and forces.While in the open Universe the gravitational force undergoes exponential suppression at cosmological distances, in the closed Universe the force induced by an individual mass is equal to zero at the antipodal point with respect to this mass. The derived formulas are applicable for investigations of the motion of astrophysical objects (e.g., galaxies) in the open and closed Universes, and for simulations of the large scale structure formation.Документ Effects of nonlinearity of f (R) gravity and perfect fluid in Kaluza–Klein models with spherical compactification(2020) Canay, Ezgi; Eingorn, Maxim; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWe study the effects associated with nonlinearity of f (R) gravity and of the background perfect fluid manifested in the Kaluza–Klein model with spherical compactification. The background space-time is perturbed by a massive gravitating source which is pressureless in the external space but has an arbitrary equation of state (EoS) parameter in the internal space. As characteristics of a nonlinear perfect fluid, the squared speeds of sound are not equal to the background EoS parameters in the external and internal spaces. In this setting, we find exact solutions to the linearized Einstein equations for the perturbed metric coefficients. For nonlinear models with f (R0) = 0, we show that these coefficients acquire correction terms in the form of two summed Yukawa potentials and that in the degenerated case, the solutions are reduced to a single Yukawa potential with some “corrupted” prefactor (in front of the exponential function), which, in addition to the standard 1/r term, contains a contribution independent of the three-dimensional distance r . In the linear f (R) = 0 model, we generalize the previous studies to the case of an arbitrary nonlinear perfect fluid. We also investigate the particular case of the nonlinear background perfect fluid with zero speed of sound in the external space and demonstrate that a non-trivial solution exists only in the case of f (R0) = 0.Документ FINE TUNING PROBLEM IN FIVE-DIMENSIONAL BRANE WORLD MODELS(Astroprint, 2012) Fakhr, S. H.; Eingorn, Maxim V.; Zhuk, Oleksandr I.ABSTRACT. Fine tuning can be called a main disadvantage of the Randall-Sundrum model, representing the most popular brane world model, constructed quite artificially in the five-dimensional space-time. It needs a bare multidimensional cosmological constant, which is related strictly to four-dimensional tension (the brane physical property).Документ Gravitational Interaction in the Chimney Lattice Universe †(2021) Eingorn, Maxim; McLaughlin II, Andrew; Canay, Ezgi; Brilenkov, Maksym; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWe investigate the influence of the chimney topology T T R of the Universe on the gravitational potential and force that are generated by point-like massive bodies. We obtain three distinct expressions for the solutions. One follows from Fourier expansion of delta functions into series using periodicity in two toroidal dimensions. The second one is the summation of solutions of the Helmholtz equation, for a source mass and its infinitely many images, which are in the form of Yukawa potentials. The third alternative solution for the potential is formulated via the Ewald sums method applied to Yukawa-type potentials. We show that, for the present Universe, the formulas involving plain summation of Yukawa potentials are preferable for computational purposes, as they require a smaller number of terms in the series to reach adequate precision.Документ Implementation of gravitational potential screening on large scales in an N-body code(2019) Baldi, Marco; Burgazli, Alvina; Eingorn, Maxim; Жук, Олександр Іванович; Жук, Александр Иванович; Zhuk, Oleksandr I.There was considered the Universe filled with cold dark matter in the form of discrete inhomogeneities (e.g., galax-ies) and dark energy in the form of arbitrary continuous per-fect fluids. The background space-time geometry is defined by the Friedmann metric.Документ MULTIDIMENSIONAL GIBBS DISTRIBUTION AND AN IDEAL GAS OF NON-RELATIVISTIC PARTICLES(Astroprint, 2011) Kusevich, A. E.; Eingorn, Maxim V.; Zhuk, Oleksandr I.We generalize the standard methods of quantum statistical physics and thermodynamics to the multidimensional case and apply them in order to derive different thermodynamic quantities, characterizing an ideal gas of non-relativistic particles. In particular, we obtain the formula for the pressure in the internal space.Документ MULTIDIMENSIONAL SOLITONS WITH SPHERICAL COMPACTIFICATION(Astroprint, 2012) Chopovsky, Oleksii V.; Eingorn, Maxim V.; Zhuk, Oleksandr I.ABSTRACT. Multidimensional static spherically symmetric (with respect to the external 3-dimensional space) vacuum solutions of the Einstein equation were well-known and prevalent in literature for a long time. These solutions are called solitons. Among them, there is a class of particular solutions, called latent solitons, which are indistinguishable from General Relativity concerning the gravitational tests. Black strings and black branes belong to this class. We construct an exact soliton solution, when the internal space represents a sphere of some finite radius.Документ QUINTESSENCE AND PHANTOM ENERGY INHOMOGENEITIES AT LATE STAGES OF UNIVERSE EVOLUTION(Astroprint, 2012) Burgazli, A. Yu.; Eingorn, Maxim V.; Zhuk, Oleksandr I.ABSTRACT. As it directly follows from the scalar perturbations, applied to the late stages of evolution of the Universe, filled with dark energy, nonrelativistic matter and, possibly, quintessence or phantom energy, the last two components can not be homogeneous. We demonstrate that ω=-1/3 is only admissible negative parameter in the non-vacuum equation of state, determine the corresponding gravitational potentials and discuss their main properties.Документ RELATIVISTIC EFFECTS IN A SYSTEM OF GRAVITATIONALLY INTERACTING NON-DUST-LIKE PARTICLES(Astroprint, 2012) Shevchenko, J. A.; Eingorn, Maxim V.; Zhuk, Oleksandr I.ABSTRACT. The two-body problem in the Kaluza– Klein model with toroidal topology of additional spatial dimensions is investigated. The characteristic property of the considering gravitational field sources is the existence of tension into the compact subspace, which is necessary to achieve the agreement with experimental restrictions on the PPN-parameter. It is shown that the two-body problem does not possess the essential symmetry and is inconsistent in the abovementioned model.Документ Scalar and vector perturbations in a universe with nonlinear perfect fluid(2021) Canay, Ezgi; Ruslan, Brilenkov; Eingorn, Maxim; Arapo˘glu, A. Savas; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWe study a three-component universe filled with dust-like matter in the form of discrete inhomogeneities (e.g., galaxies) and perfect fluids characterized by linear and nonlinear equations of state. Within the cosmic screening approach, we develop the theory of scalar and vector perturbations. None of the energy density contrasts associated with the distinct components is treated as small. Consequently, the derived equations are valid at both sub- and super-horizon scales and enable simulations for a variety of cosmological models.Документ SCHWARZSCHILD-DE SITTER AND MECHANICAL APPROACHES COMPARISON WITH RESPECT TO DARK MATTER HALOS(Astroprint, 2013) Brilenkov, R. D.; Eingorn, Maxim V.; Zhuk, Oleksandr I.We compare the Schwarzschild-de Sitter approach to deriving mass and potential distributions and corresponding parameters associated with dark matter halos for clusters of galaxies with the mechanical one, taking into account cosmological effects, in particular, dark energy influence.Документ The form of the gravitational potential in flat, open and closed Universes(2019) Eingorn, Maxim V.; Yükselci, A. E.; Zhuk, Oleksandr I.; Жук, Олександр Іванович; Жук, Александр ИвановичWithin the cosmic screening approach, we obtain the exact formulas for the velocity-independent gravitational potentials produced by matter in the form of discrete sources distributed in the flat, open and closed Universes.Документ THE NEGATIVE RESULT OF GRAVITATIONAL TESTS FOR KALUZA-KLEIN MODELS WITH SPHERICAL COMPACTIFICATION OF ADDITIONAL DIMENSIONS(Astroprint, 2011) Chopovsky, Oleksii V.; Eingorn, Maxim V.; Zhuk, Oleksandr I.We investigated classical gravitational tests for the Kaluza-Klein model with spherical compactification of additional dimensions in the case of absence of a six-dimensional bare cosmological constant. We perturbed a background by a compact massive source with the dust-like equation of state in all spatial dimensions and obtained the solution of Einstein equations in the weakfield limit. It enabled to calculate PPN parameter γ, and we obtained a strong contradiction to observations.Документ THE NON-RELATIVISTIC LIMIT OF THE RANDALL-SUNDRUM BRANE WORLD MODEL: SOLUTIONS AND APPLICATIONS(Astroprint, 2011) Kudinova, A. V.; Eingorn, Maxim V.; Zhuk, Oleksandr I.The non-relativistic limit of the Randall- Sundrum model with a single brane is investigated. Both exact and approximate expressions for the potential of a delta-shaped material source are used, some geometric configurations of the sources are considered. Formulae for the potential energy and the force of the gravitational interaction are derived, including the most important case of two balls. The constraints on the model’s parameter are obtained.