Quantum wormhole with conformal scalar field

In this paper I use the Hartle-Hawking method to discuss quantum wormhole with conformal scalar field. I derive the corresponding Wheeler-De Witt equation, calculate the wormhole wave function, which is found to be the product of two harmonic solutions. Analysis of the wave function reveals that the probability density of the wormhole appearing at a = 0 is zero, that the most probable radius of the wormhole base state is the Planck length and that the wormhole is mostly likely to be in a state of small Φ value.     

Robertson-Walker-type universes with conformally-invariant scalar field

Recently, Innaiah and Reddy (1985) obtained a flat Robertson-Walker-type solution for the Einstein field equations with the trace-free energy-momentum tensor of a conformally invariant scalar field as source. Here we show that the field equations force the scalar field to be independent of time. Furthermore, we obtain open and closed Robertson-Walker-type solutions and observe that, once again, the scalar field has to be independent of time.     

Cosmological model with a conformally coupled scalar field

Modern concepts of the universe support the assumed existence of a nongravitational source, known as dark energy, for which ε + 3 P < 0 (where ε is the energy density and P is the pressure). This ensures accelerated expansion of the universe. This paper examines a tensor-scalar variant of the theory of gravitation with a conformally coupled scalar field. Various cosmological models are examined and the possible evolutionary development of the universe with accelerated expansion is discussed. Translated from Astrofizika, Vol. 51, No. 4, pp. 653–661 (November 2008).     

Thin-shell wormholes in non-linear f(R) gravity with variable scalar curvature

The present paper explores a thin-shell wormhole (TSW) developed by employing the cut and paste method to two copies of the black hole. It develops TSW in modified $f\left(R\right)$ theory of gravity with variable scalar curvature. The effects of the model parameters on the wormhole solutions are tested, the regions of linear stability are analyzed and stable wormhole solutions have been obtained.     

Plane-symmetric dark energy model with a massive scalar field

Investigation of dark energy models in the presence of scalar fields are attracting several kinds of research because they play a vital role in the discussion of a new scenario of accelerated expansion of the universe. In this paper, we obtain an exact plane-symmetric dark energy cosmological model in the presence of an attractive massive scalar field by solving Einstein field equations using some physically relevant conditions. We have obtained all the cosmological parameters corresponding to the model. We have also presented a physical discussion of our model using a graphical representation of these parameters. The results exhibit an expanding and accelerating dark energy model of the universe, which are consistent with modern cosmological observations.     

Slowly rotating perfect-fluid universes coupled with zero-mass scalar field

Certain new analytic solutions for rotating perfect-fluid spheres in the Robertson-Walker universe are found out to substantiate the possibility of the existence of rotating cosmological objects coupled with zero-mass scalar field. Exact solutions for the metric rotation (r, t) and the matter rotation (r, t) under different conditions are obtained and their nature and role are investigated. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. In some solutions we find out the restrictions on the radii of the models for realistic astrophysical situations. Rotating models which can also be expanding are also obtained, in which case the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in the Universe.     

Magnetic stars with an external non-linear force-free field

The possible existence of strong magnetic fields in stars is discussed and a method of constructing highly distorted models of magnetic, rotating stars developed. For stars with both poloidal and toroidal fields at the surface a force-free outer boundary condition is necessary. Non-linear solutions of the force-free equations must be used. The force-free equations and the structure equations for a white dwarf are solved simultaneously by a finite difference method.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Spatially flat R-W cosmological model with massive scalar field

A spatially flat Robertson-Walker R-W cosmological model filled with a massive scalar field has been obtained for Einstein's field equations in the presence of a cosmological constant.     

Quintessential inflation models with a nonminimally coupled scalar field

The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that, unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite values during cosmological expansion. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006).     

Radiating two-fluid universe coupled with rotation interacting with a scalar field

The solution of three new interesting studies,a rotating anisotropic twofluid universe coupled with radiation and a scalar field,are studied here,where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other.In this problem,special discussion is made of the physically interesting class of models in which one fluid is a perfect comoving radiative fluid which is taken to model the cosmic microwave background and the se...     

Conformally-invariant scalar field with trace-free energy-momentum tensor in Robertson-Walker models

Exact solutions of Einstein's field equations for a conformally-invariant scalar field with trace-free energy-momentum tensor is presented for the Robertson-Walker models withK=+1, –1. The physical properties of the solution are also studied.     

Massless scalar field in Robertson-Walker space-time

Recently, exact spatially-homogeneous solutions have been found for a conformally invariant massless scalar fieldS(t) coupled to a Robertson-Walker geometry. We investigate extending these solutions to inhomogeneous scalar fieldsS(t, x ^l ). For an isotropic scalar fieldS(t, r) we find a solution satisfying three of the five field equations. If we use REDUCE, we show that the remaining equations forceS=S(t).     

Rotational perturbations of cosmological viscous-fluid Universe with zero-mass scalar field

Certain new analytic solutions for the rotational perturbations of the Robertson-Walker universe are found out to substantiate the possibility of the existence of a rotating viscous universe with zero-mass scalar field. The values for (r, t) which is related to the local dragging of inertial frames are investigated. In all the cases the rotational velocity is found to decay with time. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. The damping effect is found to be roughly analogous to viscosity. In some solutions it is found that the scalar field may exist only during a time period in the course of evolution of the Universe.     

Slow rotation of radiating viscous-fluid Universe coupled with scalar field

One of the models which have stable limit cycles but are very close to the transition of the type I intermittency is examined in some detail. The work integrals are calculated for nonlinear oscillations with various amplitudes. The model reaches its limit cycle by saturation of the driving forces due to the ionized helium (He⁺) ionization. By increasing amplitudes damping becomes superior to the driving forces and so the limit cycle is stable. However, with even larger amplitudes the model becomes pulsational unstable indicating a large positive contribution to the work integral at rather deep interior. Strong luminosity drops are observed in this region during contraction phase. It is shown that the drops come from the neutral helium and hydrogen (He and H) ionization zones moved down to the deep interior at contraction phase with increasing amplitudes. A shock wave is generated by the radiation pressure at the ionization zones and propagates outwards at the phase. The zone between the ionization zones and the detached shock front is compressed locally. Thus, subsequent contraction leads the pressure at the zone becomes very high, causing remarkable enhancement of the opacities. Thus the driving becomes to work efficiently. This is a main driving force with finite amplitudes beyond the limit cycle, and makes the model to have an unstable fixed point beyond it.     

Rotating charged perfect-fluid universes coupled with scalar field in general relativity

Certain new analytic solutions for slowly-rotating charged perfect-fluid universes coupled with zero-mass scalar field are found out to substantiate the possibility of the existence of rotating cosmological objects of such nature and their dynamics is investigated. The nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) under different conditions are studied. The effects of the charged field and the scalar field on the rotational motion are also discussed. In some solutions we find out the temporal restrictions on the models for real astrophysical situations. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time, and these models may be taken as good examples of real astrophysical objects in this Universe.     

Massive scalar field interacting with viscous fluid distribution in cosmological models

The study of Einstein's field equations describing Robertson-Walker cosmological models with massive scalar field and viscous fluid representing the matter has been made. The problem has been investigated with and without the source density in the wave equation. Corresponding exact solutions of the field equations have been obtained under different physical equations of state: namely, (i) dust distribution, (ii) Zeldovich fluid distribution, (iii) disordered distribution of radiation subject to physically realistic conditions. The physical interpretations of the physically realistic solutions has been investigated. It has been found that physically realistic solutions has been obtained for closed cosmological models only.     

Rotational perturbations of magneto-viscous fluid universes coupled with zero-mass scalar field

The dynamics of slowly rotating magneto-viscous fluid universe coupled with zero-mass scalar field is investigated, and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of several new analytic solutions. Four different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation(r,t) are discussed. Except for the case of perfect drag, the scalar field is found to have a damping effect on the rotational motion. This damping effect is seen to be roughly analogous to the viscosity. The periods of physical validity of some of the models are also found out. Most of the rotating models obtained here come out to be expanding ones as well which may be taken as good examples of real astrophysical situations.     

Robertson-Walker type model with conformally invariant scalar field with trace-free energy momentum tensor

A non-static exact solution of the Einstein equations corresponding to a conformally invariant scalar field with trace-free energy momentum tensor is obtained for the Robertson-Walker type metric. Some physical properties of the solution are discussed.