共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Arbab I. Arbab 《中国物理快报》2008,25(12):4497-4500
We investigate a cosmological model of a phantom energy with a variable cosmological constant (∧) depending on the energy density (ρ) as ∧∝ρ^α,α=const and a variable gravitational constant G. The model requires α 〈 0 and a negative gravitational constant. The cosmological constant evolves with time as ∧ ∝ t^-2. For ω 〉 - 1 and α 〈 -1 the cosmological constant ∧ 〈 0, G 〉 0 and ρ decrease with cosmic expansion. For ordinary energy (or dark energy), i.e.ω 〉 -1, we have -1 〈 α〈 0 and β 〉 0 so that G〉0 increases with time and p decreases with time. Cosmic acceleration with dust particles is granted, provided -2/3 〈α〈 0 and ∧〉0. 相似文献
3.
4.
Einstein's equations with variable gravitational and cosmological constants are considered in the presence of bulk viscosity for a Bianchi type I model in a way which conserves the energy momentum tensor. Several solutions are found, one of which corresponds to the earlier solution found by Tarkeshwar Singh et al. for the isotropic case. Our approach is compared with that of Arbab. 相似文献
5.
H. Baysal I. Yllmaz 《中国物理快报》2007,24(8):2185-2188
Einstein's field equations with C and A both varying with time are considered in the presence of a perfect fluid for five-dimensional cosmological model in a way which conserves the energy momentum tensor of the matter content. Several sets of explicit solutions in the five-dimensional Kaluza-Klein type cosmological models with variable G and A are obtained. The diminishment of extra dimension with the evolution of the universe for the five-dimensional model is exhibited. The physical properties of the models are examined. 相似文献
7.
Utpal Mukhopadhyay Partha Pratim Ghosh Saibal Ray 《International Journal of Theoretical Physics》2010,49(7):1622-1627
Two phenomenological models of Λ, viz. L ~ ([(a)\dot]/a)2\Lambda \sim (\dot{a}/a)^{2} and L ~ [(a)\ddot]/a\Lambda \sim \ddot{a}/a are studied under the assumption that G is a time-variable parameter. Both models show that G is inversely proportional to time as suggested earlier by others including Dirac. The models considered here can be matched
with observational results by properly tuning the parameters of the models. Our analysis shows that L ~ [(a)\ddot]/a\Lambda \sim \ddot{a}/a model corresponds to a repulsive situation and hence correlates with the present status of the accelerating Universe. The
other model L ~ ([(a)\dot]/a)2\Lambda \sim (\dot{a}/a)^{2} is, in general, attractive in nature. Moreover, it is seen that due to the combined effect of time-variable Λ and G the Universe evolved with acceleration as well as deceleration. This later one indicates a Big Crunch. 相似文献
8.
A cosmological model in which the universe has its critical density and gravitational constants generalized as coupling scalars in Einstein's theory is considered. A general method of solving the field equations is given. An exact solution for matter distribution in cosmological models satisfying G=G0(R/R0)n is presented. Corresponding physical interpretations of the cosmological solutions are also discussed. 相似文献
9.
Einstein's equations with variable gravitational and cosmological constants are considered in the presence of bulk viscosity for the spatially flat homogeneous and isotropic universe in a way which conserves the energy momentum tensor. A solution is found in which the cosmological term varies inversely with the square of time. Our approach is compared with that of Arbab. 相似文献
10.
Arbab I. Arbab 《中国物理快报》2008,25(10):3834-3836
We consider a cosmological model with bulk viscosity η and variable cosmological A ∝p^-α, alpha = const and gravitational G constants. The model exhibits many interesting cosmological features. Inflation proceeds du to the presence of bulk viscosity and dark energy without requiring the equation of state p =-p. During the inflationary era the energy density p does not remain constant, as in the de-Sitter type. Moreover, the cosmological and gravitational constants increase exponentially with time, whereas the energy density and viscosity decrease exponentially with time. The rate of mass creation during inflation is found to be very huge suggesting that all matter in the universe is created during inflation. 相似文献
11.
G. C. Samanta 《International Journal of Theoretical Physics》2013,52(11):4015-4024
Two-fluid anisotropic Bianchi type-III cosmological model is investigated with variable gravitational constant G and cosmological constant Λ in the framework of Einstein’s general relativity. In the two-fluid model, one fluid represents the matter content of the universe and another fluid is chosen to model the cosmic microwave background radiation. The dynamics of the anisotropic universe with variable G and Λ are discussed. We also discussed in detail the behavior of associated fluid parameters and kinematical parameters. 相似文献
12.
We have considered higher dimensional cosmological models of the FRW model with variable G and Λ. The solutions have been obtained for flat model with particular form of cosmological constant. The cosmological parameters
have also been obtained for dust, radiation and stiff matter. Physical parameters of the models are discussed. 相似文献
13.
Arbab I. Arbab 《General Relativity and Gravitation》1998,30(9):1401-1405
Exact solutions for an anisotropic Bianchi type I model with bulk viscosity and variable G and are obtained. We have found some solutions that correspond to our earlier work for the isotropic one. Unlike Kalligas et al., an inflationary solution with a variable energy density has been found where the anisotropy energy decreases exponentially with time. There is a period of hyper-inflation during which the energy density remains constant. 相似文献
14.
In this paper, we have studied the cosmological models of Bianchi type-I universes in a different basic form filled with bulk viscous fluid, in the presence of time-dependent gravitational as well as cosmological constants. A set of new exact cosmological solutions have been obtained in both full and truncated causal theories. These solutions are suitable for describing the evolution of the universe in its early stages. The physical and dynamical consequences have been discussed in detail. 相似文献
15.
The mathematical framework of Relativistic Schrödinger Theory (RST) is generalized in order to include the self-interactions of the particles as an integral part of the theory (i.e. in a non-perturbative way). The extended theory admits a Lagrangean formulation where the Noether theorems confirm the existence of the conservation laws for charge and energy–momentum which were originally deduced directly from the dynamical equations. The generalized RST dynamics is applied to the case of some heavy helium-like ions, ranging from germanium (Z=32) to bismuth (Z=83), in order to compute the interaction energy of the two electrons in their ground-state. The present inclusion of the electron self-energies into RST yields a better agreement of the theoretical predictions with the experimental data. 相似文献
16.
Arbab Ibrahim Arbab 《中国物理快报》2008,25(1):351-351
This comment corrects the small errors in the Letter of Baysal and Yilmaz [Chin. Phys. Lett. 24 (2007) 2185], where the case of n = 1 was ignored. Meanwhile, the discussion in this comment on the case of n = -3 is novel, which shows a potential reason why today the effect of the extra dimension has not been observed. 相似文献
17.
We investigate the Bianchi type-V bulk viscous barotropic fluid cosmological model with variable gravitational constant G and the cosmological constant A, assuming the condition on metric A/A=B/B=C/C=m/tn potential aswhere A, B, and C are functions of time t, while m and n are constants. To obtain the deterministic mo del, we also assume the relations P = p - 3η H, p = 7P, η = ηop^s, where p is the isotropic pressure, η the bulk viscosity,0≤r≤1 H the Hubble constant, ηo and s are constants. Various physical aspects of the model are discussed.The case of n = 1 is also discussed to compare the results with the actual universe. 相似文献
18.
H. Baysal I. Yllmaz 《中国物理快报》2008,25(1):352-352
The results of ours are correct. There are misprints in the sign of Eq. (11) and the factor (n - 1) in Eq. (12) in our paper [Chin. Phys. Lett. 24 (2007) 2185]. We did not study special values of n = 1 and n = -3. 相似文献
19.
Bianchi type-Ⅲ bulk viscous barotropic fluid cosmological model with variables G and A is investigated. To obtain the realistic model, we assume the conditions between the metric potentials A, B, C as A/A = B/B = m1/t^N and C/C = m2/t^n, P = p - 3ηH, η =ηop^s, p=γρ, 0 ≤ γ ≤ 1, where p is isotropic pressure,η the coefficient of bulk viscosity, η0 and S the constants, H the Hubble constant, m1 = 2m2 where m1 〉 0, m2 〉 O. The solutions obtained lead to inflationary phase and the results obtained match with the observations. The case n = 1 for S = 1 is also discussed, relating the results with the observations. 相似文献
20.
A cosmological model with variable G and is considered in the framework of Israel–Stewart–Hiscock (ISH) causal theory. Power law as well as inflationary solutions are obtained. The gravitational constant is found to increase with time. 相似文献