共查询到20条相似文献，搜索用时 171 毫秒
1.
The aim of this paper is to study the warm inflation during intermediate era in the framework of locally rotationally symmetric Bianchi type I universe model. We assume that the universe is composed of inflaton and imperfect fluid having radiation and bulk viscous pressure. To this end, dynamical equations (first model field equation and energy conservation equations) under slow-roll approximation and in high dissipative regime are constructed. A necessary condition is developed for the realization of this anisotropic model. We assume both dissipation and bulk viscous coefficients variable as well as constant. We evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor–scalar ratio and running of spectral index in terms of inflaton. These cosmological parameters are constrained using recent Planck and WMAP7 probe. 相似文献
2.
In this paper, we discuss energy conditions in modified Gauss-Bonnet gravity for locally rotationally symmetric Bianchi type I universe model with perfect fluid. The matter contents are constructed to discuss the energy conditions bounds. We take two specific f(G) models along with present day values of Hubble, deceleration, jerk and snap parameters. It is found that weak and null energy conditions are satisfied while strong energy conditions are violated for both models which represents the accelerated expansion of the universe. 相似文献
3.
This paper deals with the study of dynamical or phase space analysis of Bianchi I universe in Brans-Dicke gravity with chameleon scalar field. For this purpose, the matter contents are taken to be perfect fluid with magnetic field effects described by the non-linear Maxwell Lagrangian density. By taking some ansatz for the field potential and the interaction function in chameleon cosmology, we discuss three cases: Bianchi I universe with perfect fluid, FRW universe with magnetized perfect fluid and Bianchi I universe with magnetized perfect fluid. In all cases, we calculate fixed or critical points and discuss stability of the respective configuration for radiation as well as matter dominated eras. We also evaluate some cosmological parameters in each case for matter dominated era only and investigate their cosmological implications. 相似文献
4.
D. R. K. Reddy R. L. Naidu K. Dasu Naidu T. Ram Prasad 《Astrophysics and Space Science》2013,346(1):219-223
A locally rotationally symmetric (LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A barotropic equation of state is assumed to get a determinate solution of the field equations. Also, the bulk viscous pressure is assumed to be proportional to the energy density. The physical behavior of the model is also discussed. 相似文献
5.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1984,98(2):281-286
Exact solutions of the Brans-Dicke field equations of Bianchi types-II, VIII, and IX are derived. The solutions represent locally rotationally symmetric universes with stiff matter content. 相似文献
6.
In this paper, we have investigated Bianchi type VI h , II and III cosmological model with wet dark fluid in scale invariant theory of gravity, where the matter field is in the form of perfect fluid and with a time dependent gauge function (Dirac gauge). A non-singular model for the universe filled with disorder radiation is constructed and some physical behaviors of the model are studied for the feasible VI h (h=1) space-time. 相似文献
7.
The properties of locally rotationally symmetric Bianchi type-II perfect fluid space-times are analyzed in Barber’s second
self-creation theory by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration
parameter. By assuming the equation of state p=γ
ρ, many new solutions are obtained for different era—Zel’dovich, radiation, vacuum and vacuum energy dominated. The solutions
with power-law and exponential expansion are discussed. A detailed study of geometrical and physical parameters is carried
out. The nature of singularity is also clarified in each case. 相似文献
8.
D. R. K. Reddy R. L. Naidu T. Ramprasd K. V. Ramana 《Astrophysics and Space Science》2013,348(1):241-245
A locally rotationally symmetric(LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) is used to obtain determinate solution of the field equations. We have also used the barotropic equation of state and the bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the model are also discussed. 相似文献
9.
A special law of variation for Hubble’s parameter is presented in a spatially homogeneous and anisotropic Bianchi type-I space-time
that yields a constant value of deceleration parameter. Using the law of variation for Hubble’s parameter, exact solutions
of Einstein’s field equations are obtained for Bianchi-I space-time filled with perfect fluid in two different cases where
the universe exhibits power-law and exponential expansion. It is found that the solutions are consistent with the recent observations
of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out. 相似文献
10.
Sanjay Oli 《Astrophysics and Space Science》2008,314(1-3):89-94
This paper presents anisotropic, homogeneous two-fluid cosmological models in a Bianchi type I space–time with a variable
gravitational constant G and cosmological constant Λ. In the two-fluid model, one fluid represents the matter content of the universe and another fluid is chosen to model the
CMB radiation. We find a variety of solutions in which the cosmological parameter varies inversely with time t. We also discuss in detail the behavior of associated fluid parameters and kinematical parameters. This paper pictures cosmic
history when the radiation and matter content of the universe are in an interactive phase. Here, Ω is closing to 1 throughout
the cosmic evolution.
相似文献
11.
Sanjay Oli 《Astrophysics and Space Science》2008,314(1-3):95-103
In this paper we present anisotropic, homogeneous two-fluid cosmological models in a Bianchi I space-time. These classes of
cosmological models picture two different scenarios of cosmic history; viz., when the radiation and matter content of the
universe are in interactive phase and another when the two are non-interacting. The universe is highly anisotropic in the
initial stages, however, anisotropy tapers out to insignificance in due course of cosmic evolution. In every model the anisotropy
of the space-time is determined by the density parameter Ω0 at the present epoch. For Ω0=1, the anisotropy is washed out before long. An interesting class of models, having an inflationary epoch in finite future,
is discovered.
相似文献
12.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1985,108(2):423-424
We wish to point out that the locally rotationally symmetric (LRS) Bianchi type-V electromagnetic solutions recently given by Roy and Singh (1983) on the basis of the general theory of relativity (GRT) are wrong. The correct electromagnetic solutions are nothing but the vacuum and stiff matter solutions first given by Ftaclas (1978), which have been generalized by Jantzen (1980) and independently by Lorenz (1981). 相似文献
13.
The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological model representing massive
string. The energy-momentum tensor for such string as formulated by Letelier (Phys. Rev. D 28:2414, 1983) is used to construct massive string cosmological model for which we assume that the expansion (θ) in the model is proportional to the shear (σ). This condition leads to A=B
m
, where A and B are the metric coefficients and m is proportionality constant. For suitable choice of constant m, it is observed
that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated
by massive string at the late time. Our model is in accelerating phase which is consistent to the recent observations of type
Is supernovae. Some physical and geometric behavior of the model is also discussed. 相似文献
14.
V. Fayaz H. Hossienkhani A. Farmany M. Amirabadi N. Azimi 《Astrophysics and Space Science》2014,351(1):299-306
It is shown that the acceleration of the universe can be understood by considering a f(T) gravity models. Modified teleparallel gravity theory with the torsion scalar has recently gained a lot of attention as a possible explanation of dark energy. For these f(T) gravity models, a variant of the accelerating cosmology reconstruction program is developed. We consider spatially homogenous and anisotropic Bianchi type I universe in the context of f(T) gravity. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. We reconstruct f(T) theories from two different holographic dark energy models in different time durations. For the holographic dark energy model, the dark energy dominated era with new setting up is chosen for reconstruction, and the Ricci dark energy model, radiation, matter and dark energy dominated time durations are all investigated. Finally we have obtained a modified gravity action consistent with the holographic dark energy scenario. 相似文献
15.
We investigate the anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with dark matter and anisotropic dark energy. We assume that the shear scalar \((\sigma )\) is proportional to expansion scalar \((\theta )\). A special law is introduced for two skewness parameters that describe the deviation of pressure from isotropy. This law can lead to models: the hybrid expansion, the big rip and the little rip. The behavior of the Universe is discussed depending on the numerical parameters of the models. 相似文献
16.
Some features of the Bianchi type-I universes in the presence of a fluid that wields an anisotropic equation of state (EoS)
parameter are discussed in the context of general relativity. The models that exhibit de Sitter volumetric expansion due to
the constant effective energy density (the sum of the energy density of the fluid and the anisotropy energy density) are of
particular interest. We also introduce two locally rotationally symmetric models, which exhibit de Sitter volumetric expansion
in the presence of a hypothetical fluid that has been obtained by minimally altering the conventional vacuum energy. In the
first model, the directional EoS parameter on the x axis is assumed to be −1, while the ones on the other axes and the energy density of the fluid are allowed to be functions
of time. In the second model, the energy density of the fluid is assumed to be constant, while the directional EoS parameters
are allowed to be functions of time. 相似文献
17.
In this paper, we study the dynamics of warm inflation in which slow-roll inflation is driven by non-Abelian gauge fields. To this end, we use the geometry of locally rotationally symmetric Bianchi type I universe model. We construct dynamical equations, i.e., first model field equation, energy conservation equations and equation of motion under slow-roll approximation. In order to discuss inflationary perturbations, we evaluate parameters like scalar and tensor power spectra as well as scalar and tensor spectral indices. We also evaluate inflaton, directional Hubble parameter, slow-roll and perturbation parameters as well as tensor-scalar ratio as a function of inflaton during intermediate and logamediate inflationary eras. It is concluded that anisotropic inflationary universe model with non-Abelian gauge fields remains compatible with WMAP7. 相似文献
18.
Sunil Kumar Tripathy Dipanjali Behera Tushar Ranjan Routray 《Astrophysics and Space Science》2010,325(1):93-97
Spatially homogeneous and anisotropic 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. 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 physical and kinematical properties of the models are discussed.
The role of bulk viscosity in getting an inflationary phase in the universe is studied. 相似文献
19.
20.
It is shown that a suitable interaction between dark energy and dark matter in locally rotationally symmetric (LRS) Bianchi-I space-time can solve the coincidence problem and not contradict the accelerated expansion of present Universe. The interaction parameters are estimated from observational data. 相似文献