Exact interior and exterior solutions to Einstein's field equations are derived for vacuum strings. The exterior solution for a uniform density vacuum string corresponds to a conical space while the interior solution is that of a spherical cap. For Mu equals 0-1/4 the external metric is ds-squared = -dt-squared + dr-squared + (1-4 Mu)-squared r-squared dphi-squared + dz-squared, where Mu is the mass per unit length in the string in Planck masses per Planck length. A maximum mass per unit length for a string is 6.73 x 10 to the 27th g/cm. It is shown that strings cause temperature fluctuations in the cosmic microwave background and produce equal brightness double QSO images separated by up to several minutes of arc. Formulae for lensing probabilities, image splittings, and time delays are derived for strings in a realistic cosmological setting. String searches using ST, the VLA, and the COBE satellite are discussed.

Gravitational Lensing Effects of Vacuum Strings: Exact Solutions

Der speziellen Relativitatstheorie liegt folgendes Postulat zugrunde, welchem auch durch die Galilei-Newtonsche Mechanik Genuge geleistet wird: Wird ein Koordinatensystem K so gewahlt, das in bezug auf dasselbe die physikalischen Gesetze in ihrer einfachsten Form gelten, so gelten dieselben Gesetze auch in Bezug auf jedes andere Koordinatensystem K′, das relativ zu K in gleichformiger Translationsbewegung begriffen ist. Dieses Postulat nennen wir „spezielles Relativitatsprinzip“. Durch das Wort „speziell“ soll angedeutet werden, das das Prinzip auf den Fall beschrankt ist, das K′ eine gleichformige Translationsbewegung gegen K ausfuhrt, das sich aber die Gleichwertigkeit von K′ und K nicht auf den Fall ungleichformiger Bewegung von K′ gegen K erstreckt.

Die Grundlage der allgemeinen Relativitätstheorie

Relativity: the special theory. By J. L. Synge. Pp. 450. 76s. 1956. (North Holland Publishing Co. Amsterdam)

Phase transitions in the early universe can give rise to microscopic topological defects: vacuum domain walls, strings, walls bounded by strings, and monopoles connected by strings. This article reviews the formation, physical properties and the cosmological evolution of various defects. A particular attention is paid to strings and their cosmological consequences, including the string scenario of galaxy formation and possible observational effects of strings.

Cosmic Strings and Domain Walls

A five dimensional Kaluza-Klein cosmological model is considered in the frame work of f(R,T) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A barotropic equation of state is assumed to get a determinate solution of the field equations. Also, the bulk viscous pressure is assumed to be proportional to the energy density. The physical behavior of the model is also discussed.

https://www.tpbin.com/Uploads/Subjects/5c021f76-38bb-415b-99d3-145dace61082.pdf

Kaluza-Klein universe with cosmic strings and bulk viscosity in f ( R , T ) gravity

A class of exact nonstatic solutions is obtained for Einstein field equations in a closed elliptic Robertson-Walker spacetime filled with viscous perfect fluid in the presence of attractive scalar fields. The solutions characterize strong interaction of elementary particles. It is also shown that the massive graviton possesses zero spin.

Cosmological mesonic viscous fluid model

An anisotropic, spatially homogeneous, bulk viscous model of the universe without shear viscosity is investigated. The exact solutions of the model are derived and some physical consequences of the model are discussed.

Anisotropic, spatially homogeneous, bulk viscous cosmological model

In this paper we constructed five dimensional axially symmetric cosmological model generated by a cloud of strings with particles attached to them in Lyra manifold. Out of the two different cases obtained one case leads to the five dimensional vacuum universe in general theory of relativity while the other case yields a string cosmological model in Lyra manifold. In the cosmic string model we observed that the sum of tension density and rest energy density of strings vanishes and this model is also inflationary.

Five-dimensional axially symmetric string cosmological model in lyra manifold

In this paper we have taken an attempt to construct a five dimensional perfect fluid cosmological model within the framework of Lyra manifold. It is found that neither perfect fluid nor dust distributions survive. Finally the exact solutions of the vacuum field equations are obtained.

Non-Existence of Five Dimensional Perfect Fluid Cosmological Model in Lyra Manifold

In this paper, it is shown that five dimensional LRS Bianchi type-I string cosmological models do not survive for Geometric and Takabayasi string whereas Barotropic string i.e. ρ=ρ(λ) survives and degenerates string with ρ+λ=0 in scalar tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). Further we studied some physical and geometrical properties of the model.

G. Mohanty

Papers

Cosmological mesonic viscous fluid model

Anisotropic, spatially homogeneous, bulk viscous cosmological model

Five-dimensional axially symmetric string cosmological model in lyra manifold

Non-Existence of Five Dimensional Perfect Fluid Cosmological Model in Lyra Manifold

Five dimensional LRS Bianchi type-I string cosmological model in Saez and Ballester theory