LRS Bianchi type-II dark energy model in a scalar–tensor theory of gravitation

A locally rotationally symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and constant deceleration parameter have been investigated in the scalar-tensor theory proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). The scalar-tensor field equations have been solved by applying variation law for generalized Hubble’s parameter given by Bermann (Nuovo Cimento 74:182, 1983). The physical and kinematical properties of the model are also discussed.     

Some features of new holographic dark energy model in Hořava-Lifshitz gravity

We present H-band (1.4–1.8 μm) images of Neptune with a spatial resolution of ∼0.06″, taken with the W.M. Keck II telescope using the slit-viewing camera (SCAM) of the NIRSPEC instrument backed with Adaptive Optics. Images with 60-second integration times span 4 hours each on UT 20 and 21 August, 2001 and ∼1 hour on UT 1 September, 2001. These images were used to characterize the overall brightness distribution on Neptune, and to determine rotations periods (which translate into wind speeds) of individual cloud features.     

Kantowski–Sachs bulk viscous cosmological model in a scalar–tensor theory of gravitation

Field equations are obtained in the scalar–tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) with the aid of spatially homogenous and anisotropic Kantowski–Sachs space–time in the presence of bulk viscous fluid containing one dimensional cosmic strings. A determinate solution of the field equations is obtained, using some plausible physical conditions, which represents a Kantowski–Sach’s bulk viscous Cosmological model in the new scalar–tensor theory. Physical and kinematical properties of the model are also discussed.     

Kantowski–Sachs bulk viscous string cosmological model in Brans–Dicke theory of gravitation

This paper deals with the collapse and expansion of relativistic anisotropic self-gravitating source. The field equations for non-radiating and non-static plane symmetric anisotropic source have been evaluated. The non-radiating property of the fluid leads to evaluation of the metric functions. We have classified the dynamical behavior of gravitational source as expansion and collapse. The collapse in this case leads to the final stage without the formation of apparent horizons while such horizons exists in case of spherical anisotropic source. The matching of interior and exterior regions provides the continuity of masses over the boundary surface.     

Anisotropic universe with cosmic strings and bulk viscosity in a scalar–tensor theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-I cosmological model is obtained in a scalar–tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. Some physical and kinematical properties of the model are discussed. It is observed that the bulk viscosity has a greater role in getting an accelerated expansion of the universe in this theory.     

Cosmological evolution and?statefinder diagnostic for?new holographic dark energy model in?non?flat universe

In this paper, the holographic dark energy model with new infrared cut-off proposed by Granda and Oliveros has been investigated in spatially non flat universe. The dependency of the evolution of equation of state, deceleration parameter and cosmological evolution of Hubble parameter on the parameters of new HDE model are calculated. Also, the statefinder parameters r and s in this model are derived and the evolutionary trajectories in s−r plane are plotted. We show that the evolutionary trajectories are dependent on the model parameters of new HDE model. Eventually, in the light of SNe + BAO + OHD + CMB observational data, we plot the evolutionary trajectories in s−r and q−r planes for best fit values of the parameters of new HDE model.     

Entropy-corrected new agegraphic dark energy in Hořava-Lifshitz cosmology

We study the entropy-corrected version of the new agegraphic dark energy (NADE) model and dark matter in a spatially non-flat Universe and in the framework of Hořava-Lifshitz cosmology. For the two cases containing noninteracting and interacting entropy-corrected NADE (ECNADE) models, we derive the exact differential equation that determines the evolution of the ECNADE density parameter. Also the deceleration parameter is obtained. Furthermore, using a parametrization of the equation of state parameter of the ECNADE model as ω _Λ(z)=ω ₀+ω ₁ z, we obtain both ω ₀ and ω ₁. We find that in the presence of interaction, the equation of state parameter ω ₀ of this model can cross the phantom divide line which is compatible with the observation.     

Is there GR in the bimetric scalar-tensor theory of gravitation?

A theory of gravitation with a flat background metric and a dynamical variable (variable gravitational constant) is investigated. It is shown that such bimetric scalar-tensor theory (BSTT) generalized GR as all the solutions of GR equations and(x) = constant satisfy BSTT equations, firstly, and BSTT equations contain non-Einstein solutions with the variable, secondly. Due to this fact, the problem on the agreement of BSTT with the observational data is reduced to the problem on the agreement of GR with the observational data and to the interpretation of the solutions with the variable. The latter may prove useful for the prediction of new effects. Examples of such effects are discussed.     

Exact Bianchi type-V perfect fluid cosmological models in Brans–Dicke theory of gravitation

Exact Bianchi type-V cosmological models are obtained in a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961) in the presence of perfect fluid distribution. Some physical and geometrical properties of the models are also discussed.     

Bianchi type-I string cosmological models in bimetric theory of gravitation

Bianchi type-I string cosmological models are obtained in bimetric theory of gravitation proposed by Rosen (Gen. Relativ. Gravit. 4:435, 1973). Established the existence of string cosmological models, unlike the earlier authors, in this theory and studied some physical and geometrical properties.     

The Ω-field theory of gravitation and cosmology

The present paper presents, within the Einstein conceptual framework, a scalar field theory of gravitation. The -field, however, is not superimposed on the space-time manifold from outside the given geometry but is derived from the space-time torsion which is shown to be the generator of gravitation and inertia as well as spin. The theory predicts the three crucial tests of gravitation to the same degree of accuracy as does Einstein's theory. But it also predicts gravitational radiation emitted by a pulsating sphere and a singularity free cosmology in contradiction to Einstein's results. Above all, the scalar gravitational field can be easily quantized in the present context.     

Bianchi type–I dark energy cosmological model coupled with a massive scalar field

In the present investigation we are mainly concerned with a massive scalar field in an axially symmetric Bianchi type – I space-time. Einstein field equations are solved to obtain an exact cosmological model. We have used certain physically meaningful conditions for this purpose. Kinematical cosmological parameters are determined, and their dynamical aspects are discussed. It is observed that our model represents accelerated expansion of the Universe. It is observed that our model agrees with the scenario of accelerated expansion of the Universe confirmed by supernova 1a experimental data.     

The ‘naked’ singularity in the scalar-tensor gravitation theory

The complete analysis of possible types of non-relativistic and ultra-relativistic motions in the field of the naked singularity of the STGT is given. The problem of the infall of a monochromatic radiation emitter on the naked singularity is studied. In spite of the absence of a freezing effect in the STGT, the naked singularity is not observable, for the brightness of the falling emitter decreases much faster than in the GTR. Atrr _g , the trajectory of particles and light are quite similar to that of the GTR, and due to this fact the naked singularity is observationally indistinguishable from a black hole.