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V. D. Ivashchuk

Publications and source records attributed to V. D. Ivashchuk.

At least 91 records · Page 5Linked to original sources
arXiv2006

On time variation of G in multidimensional models with two curvatures

Expressions for G-dot are considered in a multidimensional model with an Einstein internal space and a multicomponent perfect fluid. In the case of two non-zero curvatures without matter, a mechanism for prediction of small G-dot is suggested. The result is compared with exact (1+3+6)-dimensional solutions. A two-component example with two matter sources (dust + 5-brane) and two Ricci-flat factor spaces is also considered.

gr-qc↗
arXiv2005

On avoiding cosmological oscillating behavior for S-brane solutions with diagonal metrics

In certain string inspired higher dimensional cosmological models it has been conjectured that there is generic, chaotic oscillating behavior near the initial singularity -- the Kasner parameters which characterize the asymptotic form of the metric "jump" between different, locally constant values and exhibit a never-ending oscillation as one approaches the singularity. In this paper we investigate a class of cosmological solutions with form fields and diagonal metrics which have a "maximal" number of composite electric S-branes. We look at two explicit examples in D=4 and D=5 dimensions that do not have chaotic oscillating behavior near the singularity. When the composite branes are replaced by non-composite branes chaotic oscillating

gr-qc↗
arXiv2005

Composite electric S-brane solutions with maximal number of branes and several scalar fields

A (n+1)-dimensional cosmological model with a set of scalar fields and antisymmetric (p+2)-form is considered. Some of scalar fields may have negative kinetic terms, i.e. they may describe ``phantom'' fields. For certain odd dimensions (D = 4m+1 = 5, 9, 13, ...) and (p+2)-forms (p = 2m-1 = 1, 3, 5, ...) and non-exceptional dilatonic coupling vector $\vecλ$ we obtain cosmological-type solutions to the field equations. These solutions are characterized by self-dual or anti-self-dual charge density forms Q (of rank 2m) and may describe the maximal set of branes (i.e. when all the branes have non-zero charge densities). Some properties of these solutions are considered, e.g. Kasner-like behavior, the existence of non-singular (e.g. bouncing) solutions and those with acceleration. The solutions with bouncing and acceleration take place when at least there is one ``phantom'' field in the model.

hep-th↗
arXiv2005

Composite Electric $s$-Brane Solutions with Maximal Charge Densities

In this paper we consider $(n+1)$-dimensional cosmological model with scalar field and antisymmetric $(p+2)$-form. Using an electric composite $Sp$-brane ansatz the field equations for the original system reduce to the equations for a Toda-like system with $n(n-1)/2$ quadratic constraints on the charge densities. For certain odd dimensions ($D = 4m+1 = 5, 9, 13, ...$) and $(p+2)$-forms ($p = 2m-1 = 1, 3, 5, ...$) these algebraic constraints can be satisfied with the maximal number of charged branes (i.e.} all the branes have non-zero charge densities). These solutions are characterized by self-dual or anti-self-dual charge density forms $Q$ (of rank $2m$). For these algebraic solutions with the particular $D$, $p$, $Q$ and non-exceptional dilatonic coupling constant $λ$ we obtain general cosmological solutions to the field equations and some properties of these solutions are examined. In particuilar Kasner-like behavior, the existence of attractor solutions.

gr-qc↗
arXiv2005

Non-singular solutions in multidimensional model with scalar fields and exponential potential

Using developed earlier our methods for multidimensional models \cite{M1,M2,M3} a family of cosmological-type solutions in D-dimensional model with two sets of scalar fields \vecϕ and \vecψ and exponential potential depending upon \vecϕ is considered. The solutions are defined on a product of n Ricci-flat spaces. The fields from \vecϕ have positive kinetic terms and \vecψ are "phantom" fields with negative kinetic terms. For vector coupling constant obeying 0< \vecλ^2 < (D-1)/(D-2) a subclass of non-singular solutions is singled out. The solutions from this subclass are regular for all values of synchronous "time" τ\in (- \infty, + \infty). For \vecλ^2 < 1/(D-2) we get an asymptotically accelerated and isotropic expansion for large values of τ.

gr-qc↗
arXiv2005

Exact solutions in multidimensional gravity with antisymmetric forms

This topical review deals with a multidimensional gravitational model containing dilatonic scalar fields and antisymmetric forms. The manifold is chosen in the form M = M_0 x M_1 x ...x M_n, where M_i are Einstein spaces (i >0). The sigma-model approach and exact solutions in the model are reviewed and the solutions with p-branes (e.g. Majumdar-Papapetrou-type, cosmological, spherically symmetric, black-brane and Freund-Rubin-type ones) are considered.

hep-th↗
arXiv2004

Composite electric S-brane solutions with maximal number of branes

In this paper we consider (n+1)-dimensional cosmological model with scalar field and antisymmetric (p+2)-form. Using an electric composite Sp-brane ansatz the field equations for the original system reduce to the equations for a Toda-like system with n(n-1)/2 quadratic constraints on the charge densities. For certain odd dimensions (D = 4m+1 = 5, 9, 13, ...) and (p+2)-forms (p = 2m-1 = 1, 3, 5, ...) these algebraic constraints can be satisfied with the maximal number of charged branes ({\it i.e.} all the branes have non-zero charge densities). These solutions are characterized by self-dual or anti-self-dual charge density forms Q (of rank 2m). For these algebraic solutions with the particular D, p, Q and non-exceptional dilatonic coupling constant λwe obtain general cosmological solutions to the field equations and some properties of these solutions are highlighted (e.g. Kasner-like behavior, the existence of attractor solutions). We prove the absence of maximal configurations for p =1 and even D (e.g. for D =10 supergravity models and those of superstring origin).

hep-th↗
arXiv2004

S-brane solutions with acceleration in models with forms and multiple exponential potentials

A family of generalized S-brane solutions with orthogonal intersection rules and n Ricci-flat factor spaces in the theory with several scalar fields, antisymmetric forms and multiple scalar potential is considered. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. These subclasses contain sub-families of solutions with accelerated expansion of certain factor spaces. Some examples of solutions with exponential dependence of one scale factor and constant scale factors of "internal" spaces (e.g. Freund-Rubin type solutions) are also considered.

hep-th↗
arXiv2004

Composite S-Brane Solutions On Product Of Ricci-Flat Spaces

A family of generalized $S$-brane solutions with orthogonal intersection rules and $n$ Ricci-flat factor spaces in the theory with several scalar fields and antisymmetric forms is considered. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. These subclasses contain sub-families of solutions with accelerated expansion of certain factor spaces. The solutions depend on charge densities of branes, their dimensions and intersections, dilatonic couplings and the number of dilatonic fields.

hep-th↗
arXiv2003

Billiard representation for multidimensional multi-scalar cosmological model with exponential potentials

Multidimensional cosmological-type model with n Einstein factor spaces in the theory with l scalar fields and multiple exponential potential is considered. The dynamics of the model near the singularity is reduced to a billiard on the (N-1)-dimensional Lobachevsky space H^{N-1}, N = n+l. It is shown that for n > 1 the oscillating behaviour near the singularity is absent and solutions have an asymptotical Kasner-like behavior. For the case of one scale factor (n =1) billiards with finite volumes (e.g. coinciding with that of the Bianchi-IX model) are described and oscillating behaviour of scalar fields near the singularity is obtained.

hep-th↗
arXiv2003

On spherically symmetric solutions with horizon in model with multicomponent anisotropic fluid

A family of spherically symmetric solutions in the model with m-component anisotropic fluid is considered. The metric of the solution depends on parameters q_s, s = 1,...,m, relating radial pressures and the densities and contains (n -1)m parameters corresponding to Ricci-flat "internal space" metrics and obeying certain m(m-1)/2 ("orthogonality") relations. For q_s = 1 (for all s) and certian equations of state (p_i^s = \pm ρ^s) the metric coincides with the metric of intersecting black brane solution in the model with antisymmetric forms. A family of solutions with (regular) horizon corresponding to natural numbers q_s = 1,2,... is singled out. Certain examples of "generalized simulation" of intersecting M-branes in D=11 supergravity are considered. The post-Newtonian parameters βand γcorresponding to the 4-dimensional section of the metric are calculated.

gr-qc↗
arXiv2003

Cosmological solutions in multidimensional model with multiple exponential potential

A family of cosmological solutions with $(n+1)$ Ricci-flat spaces in the theory with several scalar fields and multiple exponential potential is obtained when coupling vectors in exponents obey certain relations. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. It is proved that power-law solutions may take place only when coupling vectors are linearly independent and exponential dependence occurs for linearly dependent set of coupling vectors. A subfamily of solutions with accelerated expansion is singled out. A generalized isotropization behaviours of certain classes of general solutions are found. In quantum case exact solutions to Wheeler-DeWitt equation are obtained and special "ground state" wave functions are considered.

hep-th↗
arXiv2002

Simulation of intersecting black brane solutions

A family of spherically symmetric solutions with horizon in the model with multi-component anisotropic fluid (MCAF) is obtained. The metric of any solution contains n-1 Ricci-flat ``internal space'' metrics and for certain equations of state (p_i = \pm ρ) coincides with the metric of intersecting black brane solution in the model with antisymmetric forms. Examples of simulation of intersecting M2 and M5 black branes are considered. The post-Newtonian parameters beta and gamma corresponding to the 4-dimensional section of the metric are calculated.

hep-th↗
arXiv2002

Composite fluxbranes with general intersections

Generalized composite fluxbrane solutions for a wide class of intersection rules are obtained. The solutions are defined on a manifold which contains a product of n Ricci-flat spaces M_1 x ... x M_n with 1-dimensional M_1. They are defined up to a set of functions H_s obeying non-linear differential equations equivalent to Toda-type equations with certain boundary conditions imposed. A conjecture on polynomial structure of governing functions H_s for intersections related to semisimple Lie algebras is suggested. This conjecture is valid for Lie algebras: A_m, C_{m+1}, m > 0. For simple Lie algebras the powers of polynomials coincide with the components of the dual Weyl vector in the basis of simple roots. Explicit formulas for A_1 + ... + A_1 (orthogonal), "block-ortogonal" and A_2 solutions are obtained. Certain examples of solutions in D = 11 and D =10 (II A) supergravities (e.g. with A_2 intersection rules) and Kaluza-Klein dyonic A_2 flux tube, are considered.

hep-th↗
arXiv2002

On black hole solutions in model with anisotropic fluid

A family of spherically symmetric solutions in the model with 1-component anisotropic fluid is considered. The metric of the solution depends on a parameter q > 0 relating radial pressure and the density and contains n -1 parameters corresponding to Ricci-flat ``internal space'' metrics. For q = 1 and certain equations of state the metric coincides with the metric of black brane solutions in the model with antisymmetric form. A family of black hole solutions corresponding to natural numbers q = 1,2, ... is singled out. Certain examples of solutions (e.g. containing for q =1 Reissner-Nordström, M2 and M5 black brane metrics) are considered. The post-Newtonian parameters beta and gamma corresponding to the 4-dimensional section of the metric are calculated.

gr-qc↗
arXiv2002

Composite S-brane solutions related to Toda-type systems

Composite S-brane solutions in multidimensional gravity with scalar fields and fields of forms related to Toda-like systems are presented. These solutions are defined on a product manifold R_{*} x M_1 x ... x M_n, where R_{*} is a time manifold, M_1 is an Einstein manifold and M_i (i > 1) are Ricci-flat manifolds. Certain examples of S-brane solutions related to A_1 + ... + A_1, A_m Toda chains and those with "block-orthogonal" intersections (e.g. SM-brane solutions) are singled out. Under certain restrictions imposed a Kasner-like asymptotical behaviour of the solutions is shown.

hep-th↗