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Alexander Gromov

Publications and source records attributed to Alexander Gromov.

10 recordsLinked to original sources
arXiv1999

Lemaître-Tolman-Bondi model: fractality, bang time, and Hubble law I. Initial conditions and compatibility of density and velocity laws

We start a systematic study of the Lemaître-Tolman-Bondi (LTB) model as applied to the large scale structure and its evolution. Here we study three possible initial conditions of the LTB models which are asymptotically FRW at large scales: bang time, fractal density (with fractal dimension D=2), and velocity law. Any two of these determine the third one. Fractal density and simultaneous bang time provide a quantitative estimate for the scale beyond which the deflection from the linear Hubble law is small. This border may be identified with the zero-velocity surface. For fractal density and linear Hubble law it is shown that the bang time is necessarily non-simultaneous.

gr-qc↗
arXiv1997

Singularities and asymptotic behavior of the Tolman-Bondi model

The Bondi formula for calculation of the invariant mass in the Tolman- Bondi (TB) model is interprated as a transformation rule on the set of co-moving coordinates. The general procedure by which the three arbitrary functions of the TB model are determined explicitly is presented. The properties of the TB model, produced by the transformation rule are studied. Two applications are studied: for the falling TB flat model the equation of motion of two singularities hypersurfaces are obtained; for the expanding TB flat model the dependence of size of area with friedmann-like solution on initial conditions is studied in the limit $t \to +\infty$.

gr-qc↗
arXiv1997

The Tolman-Bondi Model in the Ruban-Chernin Coordinates. 1. Equations and Solutions

The Tolman-Bondi (TB) model is defined up to some transformation of a co-moving coordinate but the transformation is not fixed. The use of an arbitrary co-moving system of coordinates leads to the solution dependent on three functions $f, F, {\bf F}$ which are chosen independently in applications. The article studies the transformation rule which is given by the definition of an invariant mass. It is shown that the addition of the TB model by the definition of the transformation rule leads to the separation of the couples of functions ($f, F$) into nonintersecting classes. It is shown that every class is characterized only by the dependence of $F$ on $f$ and connected with unique system of co-moving coordinates. It is shown that the Ruban-Chernin system of coordinates corresponds to identical transformation. The dependence of Bonnor's solution on the Ruban-Chernin coordinate $M$ by means of initial density and energy distribution is studied. It is shown that the simplest flat solution is reduced to an explicit dependence on the coordinate $M$. Several examples of initial conditions and transformation rules are studied.

gr-qc↗
arXiv1997

Quasi-Two-Dimentional Modeling of the Self Gravitating Gas

The quasi-two-dimensional modeling of the small adiabatic perturbation on the background of the stationary configuration of the selfgravitating gas with the weak transverse nonhomogeneity approximation is presented. The space periodic character of the solution of this system is proofed.

gr-qc↗
arXiv1996

An Exact Solution with $f^2 = 1$ and $Λ\ne 0$ in the LTB model

The exact solution in the LTB model with $f^2 = 1$, $Λ\ne 0$ is studied. The initial conditions for the metrical function and its derivatives generate the solution with complicated structure including the solutions like "stripping of the shell", "collapce" and "core", or "accretion". In the limit of big time the solution allows the constant Hubble function and the density, depending on time. The transformation to the FRW model is shown. Three pictures are available by e-mail.

gr-qc↗
arXiv1996

The Analysis of Initial Conditions for the LTB Model

The Caushy problem in the LTB model is formulated. The rules of calculating three undetermined functions which defined a solution in the LTB model are presented. One example of exact nonhomogeneous model is studied. The limit transformation to the FRW model is shown.

gr-qc↗
arXiv1996

The Simplest Exact Solutions in the LTB Model

The rules of calculating three undetermined functions which defined a solution in the LTB model are used to study the class of exact nonhomogene\-ous models with $f^2(μ) = 1$, $Λ= 0$. The parameter $ν(μ)$ defined the difference between LTB and FRW models is found out and the limit transformation to the FRW model is shown. The initial conditions are present throught density and Habble function at the moment of time $τ= 0$. Two criteria of homogeneous of matter distribution are studied. The asimptotic of the present solution for $τ\rightarrow +\infty$ is studied.

gr-qc↗
arXiv1996

An Example of Exact Solution in the LTB Model

The Cauchy problem in the LTB model is formulated. The rules of calculating three undetermined functions which defined a solution in the LTB model are presented. One example of exact nonhomogeneous model is studied. The limit transformation to the FRW model is shown.

astro-ph↗
arXiv1995

Small Radius Perturbation of the Selfgravitating Gas with Cylindrical Symmetry

Self-consistent mouvement of initial perturbation in density, velocity and gravitation potentail on the background of the stationary cylindrical configuration of the gas with gravitation and pressure in Lagrange variables have been studied. The nonlinear partial differential equation for description radius motion has been obtained. The linearization of this equation is reduced to a Klein-Gordon equation which has an analytical solution.

astro-ph↗