共查询到20条相似文献,搜索用时 100 毫秒
1.
K. S. Adhav A. S. Bansod S. L. Munde M. S. Desale 《International Journal of Theoretical Physics》2011,50(8):2573-2581
We have studied the Bianchi type-V cosmological models with binary mixture of perfect fluid and dark energy in five dimensions.
The perfect fluid is obeying the equation of state p=γρ with γ∈[0,1]. The dark energy is considered to be either the quintessence or the Chaplygin gas. The exact solutions of the Einstein’s
field equations are obtained in quadrature form. 相似文献
2.
In this paper we have obtained some new exact solutions of Einstein’s field equations in a spatially homogeneous and anisotropic
Bianchi type-V space-time with perfect fluid distribution along with heat-conduction and decaying vacuum energy density Λ
by applying the variation law for generalized Hubble’s parameter that yields a constant value of deceleration parameter. We
find that the constant value of deceleration parameter is reasonable for the present day universe. The variation law for Hubble’s
parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The cosmological constant Λ is found to be a decreasing function of time and positive
which is corroborated by results from recent supernovae Ia observations. Expressions for look-back time-redshift, neoclassical
tests (proper distance d(z)), luminosity distance red-shift and event horizon are derived and their significance are described in detail. The physical
and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed. 相似文献
3.
Bianchi type I cosmological models with time-varying cosmological constant Λ and bulk viscous fluid are investigated. Cosmic
matter is chosen to obey a barotropic equation of state. Exact solutions of Einstein’s field equations are obtained assuming
the volume expansion θ proportional to the eigen values of shear tensor σ
ij
. Physical and kinematical properties of the models are discussed considering bulk viscosity to be a power function of matter
density. 相似文献
4.
A class of new LRS Bianchi type-I cosmological models with a variable cosmological term is investigated in presence of perfect
fluid. A procedure to generate new exact solutions to Einstein’s field equations is applied to LRS Bianchi type-I space-time.
Starting from some known solutions a class of new perfect fluid solutions of LRS Bianchi type-I are obtained. The cosmological
constant Λ is found to be positive and a decreasing function of time which is supported by results from recent supernovae Ia observations.
The physical and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed. 相似文献
5.
Anirudh Pradhan H. Amirhashchi H. Zainuddin 《International Journal of Theoretical Physics》2011,50(1):56-69
A new class of exact solutions of Einstein’s modified field equations in inhomogeneous space-time for perfect fluid distribution
with electromagnetic field is obtained in the context of normal gauge for Lyra’s manifold. We have obtained solutions by considering
the time dependent displacement field. The source of the magnetic field is due to an electric current produced along the z-axis. Only F
12 is a non-vanishing component of the electromagnetic field tensor. It has been found that the displacement vector β(t) behaves like the cosmological constant Λ in the normal gauge treatment and the solutions are consistent with the recent observations of Type Ia supernovae. Physical
and geometric aspects of the models are also discussed in the presence of magnetic field. 相似文献
6.
C. P. Singh 《Pramana》2008,71(1):33-48
The effect of bulk viscosity on the early evolution of Universe for a spatially homogeneous and isotropic Robertson-Walker
model is considered. Einstein’s field equations are solved by using ‘gamma-law’ equation of state p = (γ − 1)ρ, where the adiabatic parameter gamma (γ) depends on the scale factor of the model. The ‘gamma’ function is defined in such a way that it describes a unified solution
of early evolution of the Universe for inflationary and radiation-dominated phases. The fluid has only bulk viscous term and
the coefficient of bulk viscosity is taken to be proportional to some power function of the energy density. The complete general
solutions have been given through three cases. For flat space, power-law as well as exponential solutions are found. The problem
of how the introduction of viscosity affects the appearance of singularity, is briefly discussed in particular solutions.
The deceleration parameter has a freedom to vary with the scale factor of the model, which describes the accelerating expansion
of the Universe.
相似文献
7.
Anil Kumar Yadav Vineet K. Yadav Lallan Yadav 《International Journal of Theoretical Physics》2009,48(2):568-578
Cylindrically symmetric inhomogeneous string cosmological models are investigated in presence of string fluid as a source
of matter. To get the three types of exact solutions of Einstein’s field equations we assume A=f(x)k(t), B=g(x)ℓ(t) and C=h(x)ℓ(t). Some physical and geometric aspects of the models are discussed. 相似文献
8.
9.
We report a new formalism to obtain solutions of Einstein-Maxwell’s equations for static spheres assuming the matter content
to be a charged perfect fluid of null-conductivity. Defining three new variablesu=4πεr
2,ν=4πpr
2
2 andw=(4π/3)(ρ+ε)r
2 whereε, ρ andε denote respectively energy densities of the electric, matter and free gravitational fields whereasp is the fluid pressure, Einstein’s field equations are rewritten in an elegant form. The solutions given by Bonnor [1], Nduka
[2], Cooperstock and De la Cruz [3], Mehra [4], Tikekar [5,6], Xingxiang [7], Patino and Rago [8] are all shown to possess
simple relations betweenu, v, andw whereas Pant and Sah’s [9] solution for which all the three functions,u, v, andw are constants is a trivial case of the present formalism, We have presented six new solutions with ε = 2ρ. For the first
three solutionsw andu are constants withv as a variable whereas the remaining three solutions satisfy the equation of state for isothermal gas;v =kw =-ku where (i)k is an arbitrary constant but not equal to 1 or 1/3 (ii)k = 1 and (iii)k = 1/3. We also obtained a generalization of Cooperstock and De la Cruz’s [3] solution which is regular for 2ρ > ε but singular
for 2ρ ≤ ε. 相似文献
10.
R. J. Wiltshire 《General Relativity and Gravitation》2012,44(4):941-957
The Kerr solution for empty space-time is presented in an ellipsoidally symmetric coordinate system and it is used to produce
generalised ellipsoidal metrics appropriate for the generation of rotating interior solutions of Einstein’s equations. It
is shown that these solutions are the familiar static perfect fluid cases commonly derived in curvature coordinates but now
endowed with rotation. These are also shown to be potential fluid sources for not only Kerr but also Kerr-de Sitter empty
space-time. The approach is further discussed in the context of T-solutions of Einstein’s equations and the vacuum T-solution
outside a rotating source is presented. The interior source for these solutions is shown not to be a perfect fluid but rather
an anisotropic three component perfect fluid for which the energy momentum tensor is derived. The Schwarzschild interior solution
is given as an example of the approach. 相似文献
11.
12.
Eckehard W. Mielke 《General Relativity and Gravitation》2008,40(6):1311-1325
The curvature-squared model of gravity, in the affine form proposed by Weyl and Yang, is deduced from a topological action
in 4D. More specifically, we start from the Pontrjagin (or Euler) invariant. Using the BRST antifield formalism with a double
duality gauge fixing, we obtain a consistent quantization in spaces of double dual curvature as classical instanton type background. However,
exact vacuum solutions with double duality properties exhibit a ‘vacuum degeneracy’. By modifying the duality via a scale breaking term, we demonstrate that only Einstein’s equations with an induced cosmological constant emerge for the topology of the macroscopic background. This may have repercussions on the problem of ‘dark energy’ as well as ‘dark matter’ modeled
by a torsion induced quintaxion. 相似文献
13.
Einstein’s field equations are considered for a locally rotationally symmetric Bianchi Type-II space-time in the presence
of a massless scalar field with a scalar potential. Exact solutions of scale factors and other physical parameters are obtained
by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. To get
inflationary solutions, a flat region is considered in which the scalar potential is constant. Power-law and exponential cases
are studied and in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity.
A detailed study of geometrical and kinematical properties of solutions has been carried out.
相似文献
14.
Bianchi type-V string cosmological models in general relativity are investigated. To get the exact solution of Einstein’s
field equations, we have taken some scale transformations used by Camci et al [Astrophys. Space Sci.
275, 391 (2001)]. It is shown that Einstein’s field equations are solvable for any arbitrary cosmic scale function. Solutions
for particular forms of cosmic scale functions are also obtained. Some physical and geometrical aspects of the models are
discussed. 相似文献
15.
Hristu Culetu 《Central European Journal of Physics》2008,6(2):317-320
We take a null hypersurface (causal horizon) generated by a congruence of null geodesics as the boundary of the Doran-Lobo-Crawford
spacetime to be the place where the Brown-York quasilocal energy is located. The components of the outer and inner stress
tensors are computed and shown to depend on time and on the impact parameter b of the test-particle trajectory. The spacetime is a solution of Einstein’s equations with an anisotropic fluid as source.
The surface energy density σ on the boundary is given by the same expression as that obtained previously for the energy stored on a Rindler horizon. For
time intervals long compared to b (when the stretched horizon tends to the causal one), the components of the stress tensors become constant.
相似文献
16.
J. Podolský 《Czechoslovak Journal of Physics》2002,52(1):1-10
A physical interpretation of theC-metric with a negative cosmological constantΛ is suggested. Using a convenient coordinate system it is demonstrated that this class of exact solutions of Einstein’s equations
describes uniformly accelerating (possibly charged) black holes in anti-de Sitter universe. Main differences from the analogous
de Sitter case are emphasised.
Dedicated to my academic teacher Prof. J. Bičák on the occasion of his 60th birthday.
This work was supported by the grant GACR-202/99/0261 of the Czech Republic and GAUK 141/2000 of Charles University in Prague. 相似文献
17.
H.-O. Kreiss O. Reula O. Sarbach J. Winicour 《Communications in Mathematical Physics》2009,289(3):1099-1129
We consider the initial-boundary value problem for systems of quasilinear wave equations on domains of the form [0, T] × Σ, where Σ is a compact manifold with smooth boundaries ∂Σ. By using an appropriate reduction to a first order symmetric
hyperbolic system with maximal dissipative boundary conditions, well posedness of such problems is established for a large
class of boundary conditions on ∂Σ. We show that our class of boundary conditions is sufficiently general to allow for a well
posed formulation for different wave problems in the presence of constraints and artificial, nonreflecting boundaries, including
Maxwell’s equations in the Lorentz gauge and Einstein’s gravitational equations in harmonic coordinates. Our results should
also be useful for obtaining stable finite-difference discretizations for such problems. 相似文献
18.
The paper deals with a spatially homogeneous and totally anisotropic Bianchi II cosmological models representing massive strings
in normal gauge for Lyra’s manifold. The modified Einstein’s field equations have been solved by applying variation law for
Hubble’s parameter. This law generates two type of solutions for average scale factor, one is of power law type and other
is of exponential law type. The power law describes the dynamics of Universe from big bang to present epoch while exponential
law seems reasonable to project dynamics of future Universe. It has been found that the displacement vector (β) is a decreasing function of time and it approaches to small positive value at late time, which is collaborated with Halford
(Aust. J. Phys. 23, 863, 1970) as well as recent observations of SN Ia. The study reveals that massive strings dominate in early Universe and eventually
disappear from Universe for sufficiently large time, which is in agreement with the current astronomical observations. 相似文献
19.
Utpal Mukhopadhyay Saibal Ray A. A. Usmani Partha Pratim Ghosh 《International Journal of Theoretical Physics》2011,50(3):752-759
We perform a deductive study of accelerating Universe and focus on the importance of variable time-dependent Λ in the Einstein’s
field equations under the phenomenological assumption, Λ=αH
2 for the full physical range of α. The relevance of variable Λ with regard to various key issues like dark matter, dark energy, geometry of the field, age
of the Universe, deceleration parameter and barotropic equation of state has been trivially addressed. The deceleration parameter
and the barotropic equation of state parameter obey a straight line relationship for a flat Universe described by Friedmann
and Raychaudhuri equations. Both the parameters are found identical for α=1. 相似文献
20.
An interior spherically symmetric solution of Einstein’s field equations corresponding to perfect fluid plus a flowing radiation-field
is presented. The physical 3-spacet=constant of our solution is spheroidal. Vaidya’s pure radiation field is taken as the exterior solution. The inward motion
of the collapsing boundary surface follows from the equations of fit. An approximation procedure is used to get a generalization
of the standard Oppenheimer-Snyder model of collapse with outflow of radiation. One such explicit solution has been given
correct to second power of eccentricity of the spheroidal 3-space. 相似文献