Wormholes and the Fermi field

In this paper, we discuss the wormhole model with the coupled Fermi field, deduce the corresponding equations and give an analytical solution of them.     

Dispersion of ensembles of non-interacting particles

The dynamics of an ensemble of particles emanating from a common point with a distribution of velocities is modeled as a continuum of particles described by a phase space distribution function. A general solution for the distribution function and the associated spatial density function is obtained for a general dynamical system. The special cases of linear dynamical systems and slow dispersion from a circular orbit are treated in detail. A transcendental equation is derived, the roots of which determine the time since initial dispersion from knowledge of the spatial density function at later times.     

Kelvin-Helmholtz discontinuity in two superposed viscous conducting fluids

The Kelvin-Helmholtz discontinuity in two superposed viscous conducting fluids has been investigated in the presence of a two-dimensional horizontal uniform magnetic field. The streaming motion is also assumed to be two-dimensional. The stability analysis has been carried out for two highly viscous fluids of uniform densities. It is found that the streaming motion has dual influence on the unstable system, destabilizing for low values of streaming velocity and stabilizing for high values of streaming velocity. The effect of viscosity is, however, found to be stabilizing as the growth rate of the unstable configuration decreases on increasing the viscosity.     

Rayleigh-Taylor instability of two viscous superposed rotating and conducting fluids

Classical R-M and synthetic W-D analysis of V758 Centauri are presented. Two solutions (semi-detached and contact) were found from differential corrections approach. The semi-detached model is physically acceptable since the system is thermally decoupled. The solution for this case and the photometric data are consistent with a B9 primary and A9 secondary components having parameters close to Main-Sequence values. It is suggested that V758 Centauri is a B-type W UMa system at the brokencontact phase predicted by the Thermal Relaxation Oscillations theory.     

Kelvin-Helmholtz instability of two viscous superposed rotating and conducting fluids

Kelvin-Helmholtz instability of the interface separating two viscous rotating-conducting fluids has been studied in the presence of finite ion-Larmor radius (FLR) effects. Emloying the normal mode technique, the solutions have been obtained when the fluids are assumed to be permeated by a uniform horizontal magnetic field. For the case of two highly viscous fluids, the dispersion relation has been derived and solved numerically. It is found that the streaming velocity has a stabilizing influence on the potentially unstable arrangement of the fluids. The viscosity and FLR effects are also found to have a stabilizing influence while the Coriolis forces have a destabilizing influence on the system.     

Stability of two superposed homogeneous fluids under uniform magnetic field

The instability of two superposed homogeneous fluids is discussed under gravitational force and uniform magnetic field. The perturbation propagation is taken simultaneously along and perpendicular to streaming motion in the horizontal plane z=0. The critical wave numberk ^* has been found and some special cases of interest are discussed.     

Canonical and phantom scalar fields as an interaction of two perfect fluids

In this article we investigate and develop specific aspects of Friedmann-Robertson-Walker (FRW) scalar field cosmologies related to the interpretation that canonical and phantom scalar field sources may be interpreted as cosmological configurations with a mixture of two interacting barotropic perfect fluids: a matter component ρ ₁(t) with a stiff equation of state (p ₁=ρ ₁), and an “effective vacuum energy” ρ ₂(t) with a cosmological constant equation of state (p ₂=?ρ ₂). An important characteristic of this alternative equivalent formulation in the framework of interacting cosmologies is that it gives, by choosing a suitable form of the interacting term Q, an approach for obtaining exact and numerical solutions. The choice of Q merely determines a specific scalar field with its potential, thus allowing to generate closed, open and flat FRW scalar field cosmologies.     

Charged shell supported by a phantom energy

This paper discusses the evolution of a thin spherically symmetric self gravitating phantom shell around the charged shell. The general equations describing the motion of shell with a general form of equation of state are derived. The different types of space-time R _± and T _± regions and shell motion are classified depending on the parameters of the problem. The mechanical stability analysis of this spherically symmetric thin shell with charge in Reissner-Nordstrom (RN) to linearized spherically symmetric perturbation about static equilibrium solution is carried out.     

An interacting and non-interacting two-fluid scenario for dark energy in FRW universe with constant deceleration parameter

In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic FRW universe filled with barotropic fluid and dark energy. The scale factor is considered as a power law function of time which yields a constant deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. The cosmic jerk parameter in our derived models is consistent with the recent data of astrophysical observations. It is concluded that in non-interacting case, all the three open, close and flat universes cross the phantom region whereas in interacting case only open and flat universes cross the phantom region. We find that during the evolution of the universe, the equation of state (EoS) for dark energy ω _D changes from ω _D >−1 to ω _D <−1, which is consistent with recent observations.     

Stability of charged thin shell wormhole supported by polytropic gas

In the framework of Darmois-Israel formalism, the general equations describing the motion of thin shell wormhole with a general form of equation of state of a polytropic gas are derived. The mechanical stability analysis of thin shell wormhole with charge in Reissner–Nordstrom (RN) to linearized spherically symmetric perturbation about static equilibrium solution is carried out.     

Slowly-rotating cosmological perfect fluids

The Einstein field equations for a perfect fluid distribution representing slowly-rotating fluid spheres are investigated. By imposing restrictions on the matter rotation (r, t) which is related to the dragging of inertial frames, and a uniform rotation which is a function of time, the general solutions for (r, t) are obtained for all cosmological models. In the case of closed models the solutions for (r, t) may represent realistic astrophysical situations only when the radial distance is greater than –1 and less than +1.     

Rigidly rotationg perfect fluids

A class of stationary rigidly rotating perfect fluids in General Relativity is investigated. This class which is characterized by zero Simon tensor contains only the Wahlquist solution and its limits. It is shown how a recently given solution follows from the Wahlquist solution by a limiting procedure.