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1.
The effect of bulk viscosity on the evolution of the spatially flat Friedmann-Robertson-Walker models in the context of open thermodynamical systems, which allow particle creation, is analyzed within the framework of Brans-Dicke theory. Particle creation and bulk viscosity have been considered as separated irreversible processes. To accommodate the viscous pressure and creation pressure, which is associated with creation of matter out of gravitational field, the energy-momentum tensor is modified. Dynamical behaviour of the models have been discussed.  相似文献   

2.
The Bianchi type-V cosmological model with viscous fluid and creation particle in Brans-Dicke theory has been considered. The present paper deals with Bianchi type-V cosmological model with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We have discussed two types of solutions of the average scale factor for a Bianchi type-V model by using a variation law of Hubble’s parameter, which yields a constant value of the deceleration parameter. The exact solutions to the corresponding field equations are obtained in quadrature form. The solutions to the Einstein field equations are obtained for power law and exponential form. The cosmological parameters have been discussed in detail.  相似文献   

3.
Bianchi Type-V bulk viscous fluid string dust cosmological model in General Relativity is investigated. It has been shown that if coefficient of bulk viscosity (ζ) is inversely proportional to the expansion (θ) in the model then string cosmological model for Bianchi Type-V space-time is possible. In absence of bulk viscosity (ζ), i.e. when ζ → 0, then there is no string cosmological model for Bianchi Type-V space-time. The physical and geometrical aspects of the model are also discussed.  相似文献   

4.
An LRS Bianchi Type V bulk viscous fluid dust distribution string cosmological model in General Relativity is investigated. It has been shown that if coefficient of bulk viscosity (ζ) is proportional to the expansion (θ) in the model then string cosmological model for Bianchi Type V space-time is possible. In absence of bulk viscosity(ζ) i.e. when ζ → 0 then there is no string cosmological model for Bianchi Type V space-time. The physical and geometrical aspects are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed.  相似文献   

6.
The objective of the present paper is to study an anisotropic Bianchi-I cosmological model filled with bulk viscous fluid and magnetic field in string cosmology. The magnetic field is due to an electric current produced along the x-axis. The expansion in the model is considered to be proportional to one of the components of the shear tensor. We obtain two different quadrature forms of volume scale factor by considering two different relations between bulk viscosity and expansion scalar. We discuss the behavior of the classical potential with respect to the volume scale factor in the presence or absence of magnetic field and bulk viscosity in each case. We observe the role of bulk viscosity on the classical potential and also on the choices of bulk viscous pressure. By introduction of magnetic field or bulk viscosity or both into the model it results in changes in the potential as well as in volume scale factors. The physical and geometrical aspects of the solutions are discussed in detail.  相似文献   

7.
Mechanical and thermodynamic aspects of the early universe are discussed. Adopting an isotropic and imperfect fluid model, we can introduce one single viscosity coefficient, viz. the bulk viscosity . Allowing for particle creation or annihilation there is room for one additional coefficient, viz. the creation rate . Specializing to the FRW metric we consider the question, discussed in the recent literature, whether the viscosity/creation concepts describe after all one and the same physical process. We conclude that they do not. Thereafter considering the limitations on set by the second law of thermodynamics, we find that it is possible to account for the large nondimensional entropy in the universe (109) by ignoring viscosity altogether, and allowing for a particle sink (<0) of large magnitude being operative during a brief time period. Numerical examples are given.  相似文献   

8.
This paper deals with the general class of Bianchi cosmological models with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We discuss three types of average scale-factor solutions for the general class of Bianchi cosmological models by using a special law for the deceler- ation parameter which is linear in time with a negative slope. The exact solutions to the corresponding field equations are obtained in quadrature form and solutions to the Einstein field equations are obtained for three different physically viable cosmologies. All the physical parameters are calculated and discussed in each model.  相似文献   

9.
We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that the instability is effectively suppressed.   相似文献   

10.
Exact solutions are obtained for an isotropic homogeneous universe with a bulk viscous fluid in the cosmological theory based on Lyra’s geometry. The viscosity coefficient of the bulk viscous fluid is assumed to be a power function of the mass density. Cosmological models with time dependent displacement field have been discussed for a constant value of the deceleration parameter. Finally some possibilities of further problems and their investigations have been pointed out.  相似文献   

11.
The present paper reports a study of the reconstruction of f(R) gravity from holographic Ricci dark energy, a specific case of Nojiri–Odintsov holographic DE (ref Nojiri and Odinstov, 2005a), in the presence of bulk viscosity. The reconstructed equation of state (EoS) parameter wR was found to have a transition from quintessence to phantom in the absence of the bulk viscosity. Thus, the behaviour of wR for this reconstruction scheme was identified as “quintom” in the absence of the bulk viscosity. However, in the case of the bulk viscous scenario wR behaves like “quintessence”. Furthermore, the generalized second law of thermodynamics was tested in the case of the reconstructed f(R) gravity. Finally, the stability of this model against small perturbations was demonstrated with the aid of squared speed of sound.  相似文献   

12.
FRW models of universe in the presence of viscous fluid are investigated in the cosmological theory based on Lyra’s Manifold. By considering the deceleration parameter to be a variable and the viscosity coefficient of bulk viscous fluid to be a constant, exacts solutions have been obtained from which three forms of model of the universe are derived. The physical properties of the models are also investigated.  相似文献   

13.
Some locally rotationally symmetric (LRS) Bianchi type I cosmological models for a cloud string with bulk viscosity and magnetic field are presented. Where an equation of state ρ = kλ and a relation between metric potential R = AS n are considered. The solution describes a shearing and nonrotating model with a big bang start. In the absence of magnetic field it reduces to a string model with bulk viscosity, where the relation between the coefficient of bulk viscosity and energy density is ζ ∝ ρ1/2. After choosing k = , it further reduces to a string model without viscosity and magnetic field. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

14.
String cosmological models with bulk viscosity are investigated in Kantowski-Sachs space-time. To obtain a determinate solution, it is assumed that the coefficient of bulk viscosity is a power function of the scalar of expansion ζ = kθm and the scalar of expansion is proportional to the shear scalar θ ∝ σ, which leads to a relation between metric potentials R = AS n . The physical and geometrical aspects of the model are also discussed. It is shown that the bulk viscosity has significant influence on the evolution of the universe. There is a ‘big bang’ start in the model when m ≤ 1 but there is no ‘big bang’ start when m > 1.  相似文献   

15.
Hypersurface–homogeneous cosmological models containing a bulk viscous fluid with time varying G and Λ have been presented. We have shown that the field equations are solvable for any arbitrary cosmic scale function. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of the energy density. Exact solutions of Einstein’s field equations are obtained which represent an expanding, shearing and accelerating/decelerating models of the universe. The physical and kinematical behaviours of the models are also discussed.  相似文献   

16.
Spatially homogeneous and anisotropic LRSBianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings embedded in a magnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The effects of viscosity and electromagnetic field on the properties of the model are investigated. The role of bulk viscosity and electromagnetic field in getting an inflationary phase and in establishing a string phase in the universe is studied.  相似文献   

17.
An exact cosmological solution for Friedman Robertson Walker (FRW)metric is obtained with a classical scalar field φ along with a potential in the presence of a causal viscous fluid. Assuming the scale factor to be a function of the scalar field we have obtained solutions in both the truncated and the full causal theory. It is shown that an inflationary model can be obtained by imposing certain constraints on some constants. The radiative bulk viscosity during the decoupling era has also been studied as a special case. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

18.
Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without the need of introducing extra pressure terms.  相似文献   

19.
Oscillating Tolman universes have been identified as solutions of the Friedmann equation with the bulk viscosity dissipation. Their dynamics and some thermodynamical properties are briefly discussed. Problems such as the Eternal Return philosophy and its modern incarnation into the doctrine of the Universe as a global oscillator, Tipler's no-return theorem, etc., are touched upon.  相似文献   

20.
In this paper, we have investigated spatially homogeneous isotropic Friedmann cosmological model with bulk viscosity and zero-mass scalar field in Lyra manifold. The cosmological models are obtained with the help of the special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) and power law relation. Some physical properties of the models are discussed.  相似文献   

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