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Vol 22, No 4 (2016)

Article

On the equivalence of approximate stationary axially symmetric solutions of the Einstein field equations

Boshkayev K., Quevedo H., Toktarbay S., Zhami B., Abishev M.

Abstract

We study stationary axially symmetric solutions of the Einstein vacuum field equations that can be used to describe the gravitational field of astrophysical compact objects in the limiting case of slow rotation and slight deformation. We derive explicitly the exterior Sedrakyan–Chubaryan approximate solution, and express it in an analytical form, which makes it practical in the context of astrophysical applications. In the limiting case of vanishing angular momentum, the solution reduces to the well-known Schwarzschild solution in vacuum. We demonstrate that the new solution is equivalent to the exterior Hartle–Thorne solution. We establish mathematical equivalence between the Sedrakyan–Chubaryan, Fock–Abdildin and Hartle–Thorne formalisms.

Gravitation and Cosmology. 2016;22(4):305-311
pages 305-311 views

Alternative interpretation of the 1D-box solution and the Bargmann theorem

Yefremov A.P.

Abstract

Primitive mapping of 2D fractal spaces yields a formulation of the Schro¨ dinger equation and endows its solutions and the respective 3D objects with specific geometric images. In particular, it is shown that the simplest 1D-box solution comprising no parameters of particles motion can be interpreted as a 2D inhomogeneous string oscillating on a real-imaginary fractal surface or as a 3D static spindle with a harmonically distributed mass spectrum. The description of an inertially moving similar object is obtained using a Bargmann-type theorem applied to the Bohm equations, and, as their exact solution, a fractal function containing explicit kinematic terms.

Gravitation and Cosmology. 2016;22(4):312-315
pages 312-315 views

Wormholes leading to extra dimensions

Bronnikov K.A., Skvortsova M.V.

Abstract

In 6D general relativity with a scalar field as a source of gravity, a new type of static wormhole solutions is presented: such wormholes connect our universe with a small 2D extra subspace with a universe where this extra subspace is large, and the whole space-time is effectively 6-dimensional. We consider manifolds with the structure M0 × M1 × M2, where M0 is 2D Lorentzian space-time while each of M1,2 can be a 2-sphere or a 2-torus. After selecting possible asymptotic behaviors of the metric functions compatible with the field equations, we give two explicit examples of wormhole solutions with spherical symmetry in our space-time and toroidal extra dimensions. In one example, with a massless scalar field (it is a special case of a well-known more general solution), the extra dimensions have a large constant size at the “far end”; the other example contains a nonzero potential V(φ) which provides a 6D anti-de Sitter asymptotic, where all spatial dimensions are infinite.

Gravitation and Cosmology. 2016;22(4):316-322
pages 316-322 views

On nonlinear multidimensional gravity and the Casimir effect

Bolokhov S.V., Bronnikov K.A.

Abstract

We study the properties of an effective potential for the scale factor of extra dimensions in a Kaluza-Klein-type model with a spherical extra factor space, including a function of the scalar curvature and other quadratic curvature invariants, taking into account the Casimir energy of massless scalar fields. We demonstrate the existence of a minimum of the potential, able to induce a physically reasonable value of the effective cosmological constant in our space-time. Under the adopted assumptions, it is shown that the huge Casimir energy density can be compensated by the fine-tuned contribution of the curvature-nonlinear terms in the original action.

Gravitation and Cosmology. 2016;22(4):323-328
pages 323-328 views

On stable exponential solutions in Einstein–Gauss–Bonnet cosmology with zero variation of G

Ivashchuk V.D.

Abstract

A D-dimensional gravitational model with a Gauss–Bonnet term and the cosmological constant Λ is considered. Assuming diagonal cosmological metrics, we find, for certain Λ > 0, new examples of solutions with an exponential time dependence of two scale factors, governed by two Hubble-like parameters H > 0 and h < 0, corresponding to submanifolds of dimensions m and l, respectively, with (m, l) = (4, 2), (5, 2), (5, 3), (6, 7), (7, 5), (7, 6) and D = 1 + m + l. Any of these solutions describes an exponential expansion of our 3-dimensional factor space with the Hubble parameter H and zero variation of the effective gravitational constant G. We also prove the stability of these solutions in the class of cosmological solutions with diagonal metrics.

Gravitation and Cosmology. 2016;22(4):329-332
pages 329-332 views

A need to return to space project SEE for measuring G and its possible variations

Melnikov V.N.

Abstract

The SEE (Satellite Energy Exchange) mission was suggested and designed under NASA Project in 1992–2002 to make extremely accurate measurements on fundamental gravitation by observing the orbital perturbation of unconstrained orbiting test bodies in a femto-g to atto-g environment. The mission uses novel and original test body dynamics. Its broad objective is to support the development of gravity theory and its unification with other interactions by carrying out sensitive gravitational tests capable of discriminating among alternative theories. The SEE mission introduced and utilized new technology for near-zero-g environment creation, passive cryogenic temperature control, passive station-keeping capability, and non-contact sub-micron-accuracy distance measurements, all of which promise to have a wide variety of applications.

Gravitation and Cosmology. 2016;22(4):333-338
pages 333-338 views

A search for observational manifestations of de Sitter relativity

Tretyakova D.A.

Abstract

De Sitter-invariant special relativity is a natural extension of Einstein’s special relativity. Within this framework, extension of special relativity to de Sitter space-time introduces a new length scale R, serving as an origin of the geometrical cosmological constant Λ = 3/R2. De Sitter relativity predicts a departure from the Lorentz invariance due to space-time curvature, related to the geometrical cosmological constant. In this paper, the impact of de Sitter special relativity effects on threshold particle processes and equivalence principle violation is considered. The main conclusion is that the constraints coming from cosmological fine structure constant variations render this effects nowadays undetectable. A brief outlook is given thereafter.

Gravitation and Cosmology. 2016;22(4):339-344
pages 339-344 views

An AP structure with Finslerian Flavor: Path equations

Wanas M.I., Kahil M.E., Kamal M.M.

Abstract

The Bazanski approach to deriving paths is applied to Finsler geometry. The approach is generalized and applied to a new developed geometry called “Absolute parallelism with Finslerian Flavor” (FAP). A set of path equations is derived for the FAP. It is a horizontal (h) set. A striking feature in this set is that the coefficient of the torsion term jumps by a step of one-half from one equation to the other. It is tempting to believe that the h-set admits some quantum features. Comparisons with the corresponding sets in other geometries are given. Conditions for reducing the set of path equations obtained to well-known path equations in some geometries are summarized in a schematic diagram.

Gravitation and Cosmology. 2016;22(4):345-354
pages 345-354 views

The hydrogen atom allowing for gravity

Laptev Y.P., Fil’chenkov M.L.

Abstract

The hydrogen atom is comprised of a proton and an electron possessing charges and masses. The latter involves a gravitational interaction. Since hydrogen atoms are the most abundant in the Universe, their gravitational radiation proves to be of importance for cosmology.

Gravitation and Cosmology. 2016;22(4):355-357
pages 355-357 views

Equation of state for cosmological fluids: Direct dynamical derivation

Rudoy Y.G., Kalmykov A.V.

Abstract

The derivation of the “baroenergetic” equation of state is reconsidered in rather a general form following Bernoulli’s kinetic approach but with Lorentz energy-momentum dependence. It is shown that uniform versions of the equation of state generally used in cosmology are valid only in extreme limits: an ultrarelativistic photon gas (electromagnetic radiation) and a nonrelativistic gas of massive particles. Possible ways of generalization of these results are pointed out and briefly discussed.

Gravitation and Cosmology. 2016;22(4):358-362
pages 358-362 views

Three kinds of particles on a single rationally parameterized world line

Kassandrov V.V., Markova N.V.

Abstract

We consider the light cone (‘retardation’) equation (LCE) of an inertially moving observer and a single world line parameterized by arbitrary rational functions. Then a set of apparent copies, R- or C-particles, defined by (real or complex conjugate) roots of the LCE will be detected by the observer. For any rational world line the collective R-C dynamics is manifestly Lorentz-invariant and conservative; the latter property follows directly from the structure of Vieta formulas for the LCE roots. In particular, two Lorentz invariants, the square of total 4-momentum and total rest mass, are distinct and both integer-valued. Asymptotically, at large values of the observer’s proper time, one distinguishes three types of LCE roots and associated R-C particles, with specific locations and evolutions; each of three kinds of particles can assemble into compact large groups—clusters. Throughout the paper, we make no use of differential equations of motion, field equations, etc.: the collective R-C dynamics is purely algebraic.

Gravitation and Cosmology. 2016;22(4):363-367
pages 363-367 views

Scalar field with the source in the form of the stress-energy tensor trace as a dark energy model

Dudko I.G., Vyblyi Y.P.

Abstract

We consider a scalar-tensor theory of gravitation with the scalar source being the trace of the stress-energy tensor of the scalar field itself andmatter. We obtain an example of a numerical solution of the cosmological equations which shows that under some special choice of the scalar parameters, there exists a slow-roll regime in which the modern values of the Hubble and deceleration parameters may be obtained.

Gravitation and Cosmology. 2016;22(4):368-373
pages 368-373 views

Opto-acoustical gravitational bar detector with cryogenic mirrors

Kulagin V.V., Oreshkin S.I., Popov S.M., Rudenko V.N., Skvortsov M.N., Yudin I.S.

Abstract

Enhancing of sensitivity of the opto-acoustical gravitational wave (GW) antenna OGRAN installed at the underground facilities of Baksan Neutrino Observatory is analyzed. Calculations are presented, showing a sensitivity improvement by two orders of magnitude after cooling the solid acoustical part of the antenna to the nitrogen temperature. The possibility of keeping the same optical scheme of the antenna at low temperature is discussed. The design of an upgraded construction for a cryogenic version of the OGRAN antenna is described. Test experiments with a cooled pilot model carrying cryogenic mirrors illuminated by an optical pump up to 0.5Ware presented.

Gravitation and Cosmology. 2016;22(4):374-381
pages 374-381 views

A class of solutions under GUP for a harmonic oscillator and a particle in a box

Naimi Y.

Abstract

The existence of a minimal observable length is the common prediction of different theories of quantum gravity such as string theory, loop quantum gravity and black hole physics. The ordinary Heisenberg uncertainty principle (HUP) is not compatible with this prediction, so the HUP was generalized to the Generalized Uncertainty Principle (GUP) in literature. The consequences of this generalization are the generalized commutation relations between operators and so the generalized Hamiltonian for systems. In this paper, we represent the solutions of a harmonic oscillator and a particle in a box in the sense of a generalized commutation relation. We show that using of the Hellmann-Feynman (HF) theorem leads to the approximate energy spectrum of a harmonic oscillator and the exact energy spectrum of a particle in a box. In these cases, we do not solve the corresponding generalized Schro¨ dinger equation directly, but the HF theorem exhibit the effect of GUP on the energy spectrum. Also we obtain the uncertainties in both position and momentum for a harmonic oscillator and derive the GUP.

Gravitation and Cosmology. 2016;22(4):382-387
pages 382-387 views

ΛCDM type Heckmann–Schuking model and Union 2.1 compilation

Goswami G.K., Dewangan R.N., Yadav A.K.

Abstract

We study a ΛCDM type cosmological model in Heckmann-Schucking space-time, by using 287 high redshift (.3 ≤ z ≤ 1.4) SN Ia data on observed absolute magnitude along with their possible error from Union 2.1 compilation. We use the χ2 test to compare Union 2.1 compilation observed data and the corresponding theoretical values of the apparent magnitude (m). It is found that the best fit value of (Ωm)0, (ΩΛ)0 and (Ωσ)0 are 0.2940, 0.7058 and 0.0002, respectively, and the derived model represents the features of an accelerating universe which is consistent with the recent astrophysical observations.

Gravitation and Cosmology. 2016;22(4):388-393
pages 388-393 views

Inflationary scenario in Bianchi Type V space-time for a barotropic fluid distribution with variable bulk viscosity and vacuum energy density

Bali R., Singh S.

Abstract

We examine an inflationary scenario in Bianchi Type V space-time for a barotropic fluid distribution with variable bulk viscosity and decaying vacuum energy density. We observe that the matter density ρ, the coefficient of bulk viscosity ζ and the expansion θ all diverge at τ = 0. The spatial volume increases with time, representing an inflationary scenario. The deceleration parameter q < 0 for barotropic, dust and radiation dominated models representing an accelerated universe, while for a stiff fluid distribution q > 0 corresponding to a decelerated universe. The vacuum energy density Λ decreases with time. The entropy per unit volume is proportional to the absolute temperature. The energy conditions (weak, dominant and strong) are discussed for the model. The reality condition ρ + p ≥ 0 is violated for the inflationary model due to the presence of a scalar field (φ). We also discuss the importance of Bianchi Type V model where the anisotropy dies away during the inflationary era. We also calculate the inflationary parameters and compare the results with the Planck data and discuss their compatibility with anisotropy and BAO estimates. The cosmological constant Λ is a function of time without break general covariance. We also discuss the bounds of the model, how the model isotropizes, where the fluid goes after inflation and how viscosity may realize a graceful exit from inflation to a radiation dominated era.

Gravitation and Cosmology. 2016;22(4):394-403
pages 394-403 views

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