共查询到20条相似文献，搜索用时 441 毫秒
1.
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
2.
C. P. Singh 《Astrophysics and Space Science》2013,343(2):773-781
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
3.
The bulk viscosity is introduced into the frame of ordinary Friedmannian cosmology (under highly idealized assumption of the constant coefficient of bulk viscosity). Explicit solutions are given for the viscous flat universe filled with the dust-substratum and for the viscous radiative universe. The problem, how does the introduction of viscosity affect the appearance of singularity, is briefly discussed. 相似文献
4.
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
5.
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
6.
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
7.
We explore flat ΛCDM models with bulk viscosity, and study the role of the bulk viscosity in the evolution of these universe
models. The dynamical equations for these models are obtained and solved for some cases of bulk viscosity. We obtain differential
equations for the Hubble parameter H and the energy density of dark matter ρ
m
, for which we give analytical solutions for some cases and for the general case we give a numerical solution. Also we calculate
the statefinder parameters for these models and display them in the s–r-plane. 相似文献
8.
Sunil K. Tripathy Subodha K. Nayak Subrat K. Sahu Tushar R. Routray 《Astrophysics and Space Science》2009,323(3):281-287
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
9.
This paper is devoted to the study of role of particle creation and bulk viscosity on evolution of homogeneous and anisotropic
model of the universe represented by Bianchi type I space time metric. Particle creation and bulk viscosity have been considered
as separated irreversible processes. In order to discuss physical and geometrical behaviour of the model, a new set of exact
solutions of Einstein’s field equation have been obtained in non-causal, truncated and full causal theories. Dynamical behaviours
of models have also been discussed. 相似文献
10.
In this paper we study FRW bulk viscous cosmology in presence of modified Chaplygin gas. We write modified Friedmann equations due to bulk viscosity and Chaplygin gas and obtain time-dependent energy density for the special case of flat space. 相似文献
11.
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
12.
Friedmann—Lemaître cosmology is briefly reviewed in terms of dynamical systems. It is demonstrated that in certain cases bulk viscosity dissipation structurally stabilizes Friedmann—Lemaître solutions. It turns out that, for A=0, there are structurally stable solutions if ξ~ε1/2, where ξ is the bulk viscosity coefficient. For A≠0 structurally stable solutions are essentially those with ξ=const. The role of structural stability in physics and cosmology is shortly discussed. 相似文献
13.
《New Astronomy》2020
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
14.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2008,318(1-2):125-131
LRS Bianchi 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 electromagnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscosity is assumed to be inversely proportional to the scalar expansion. The physical and kinematical properties of the models are discussed. The effect of viscosity and electromagnetic field on the physical and kinematical properties is also investigated. 相似文献
15.
In this paper we study FRW bulk viscous cosmology in presence of modified cosmic Chaplygin gas. We obtain generalized Friedmann equations due to bulk viscosity and modified cosmic Chaplygin gas. Then, we calculate time-dependent energy density and discuss Hubble expansion parameter. 相似文献
16.
Xinzhong Chen Edward A. Spiegel 《Monthly notices of the Royal Astronomical Society》2001,323(4):865-871
Viscous resistance to changes in the volume of a gas arises when different degrees of freedom have different relaxation times. Collisions tend to oppose the resulting departures from equilibrium and, in so doing, generate entropy. Even for a classical gas of hard spheres, when the mean free paths or mean flight times of constituent particles are long we find a non-vanishing bulk viscosity. Here we apply a method recently used to uncover this result for a classical rarefied gas to radiative transfer theory, and derive an expression for the radiative stress tensor for a grey medium with absorption and Thomson scattering. We determine the transport coefficients through the calculation of the comoving entropy generation. When scattering dominates absorption, the bulk viscosity may be much larger than either the shear viscosity or the thermal conductivity. 相似文献
17.
Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical andgeometric aspects of the models are also discussed. 相似文献
18.
Ø. Grøn 《Astrophysics and Space Science》1990,173(2):191-225
The research on viscous cosmological models is reviewed and carried further. Inflationary cosmological models of Bianchi type-I with shear, bulk, and nonlinear viscosity are studied. The inflation field energy is represented by a two-components cosmic fluid consisting of a vacuum fluid and a Zel'dovich fluid. It is shown that there exist models in which the viscous Zel'dovich fluid removes the initial singularity of the corresponding viscosity free models. The mean expansion of a Zel'dovich dominated unvierse is found to be independent of shear viscosity and anisotropy. Bulk viscosity and shear viscosity cause exponential decay of anisotropy, while nonlinear viscosity causes power-law decay of anisotropy. 相似文献
19.
N. Andersson 《Astrophysics and Space Science》2007,308(1-4):395-402
In this brief summary I describe our recent work on superfluid neutron star dynamics. I review results on shear viscosity,
hyperon bulk viscosity, vortex mediated mutual friction and the modelling of multifluid systems in general. For each problem
I provide a set of questions that need to be addressed by future work. 相似文献
20.
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