We consider a locally rotationally symmetric(LRS)Bianchi type-Ⅱspacetime with a perfect fluid and a variable cosmological constant∧.To solve the Einstein field equations we consider the cosmological term∧to be prop...We consider a locally rotationally symmetric(LRS)Bianchi type-Ⅱspacetime with a perfect fluid and a variable cosmological constant∧.To solve the Einstein field equations we consider the cosmological term∧to be proportional to R^(-m) with R being the scale factor and m a constant[Phys.Rev.D 58(1998)043506].In this model we obtain∧~H^(2),∧~(R)/R and Larnbda~t^(-2),in agreement with the main dynamical laws for the decay of∧.The physical significance of the cosmological model is also discussed.展开更多
Einstein field equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for a Bianchi type-I universe by assuming that the cosmological term is proportional to...Einstein field equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for a Bianchi type-I universe by assuming that the cosmological term is proportional to the Hubble parameter..The variation law for vacuum density was recently proposed by Schützhold on the basis of quantum field estimation in a curved expanding background.The cosmological term tends asymptotically to a genuine cosmological constant and the model tends to a de Sitter universe.We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of a cosmological term.展开更多
We study the non existence of shear in locally rotationally symmetric Bianchi type-Ⅲstring cosmological models with bulk viscosity and variable cosmological termΛ.Exact solutions of the field equations are obtained ...We study the non existence of shear in locally rotationally symmetric Bianchi type-Ⅲstring cosmological models with bulk viscosity and variable cosmological termΛ.Exact solutions of the field equations are obtained by assuming the conditions:the bulk viscosity is proportional to the expansion scalar,ξ∝θ,expansion scalar is proportional to shear scalar,θ∝σ,and A is proportional to the Hubble parameter.The coefficient of bulk viscosity is assumed to be a power function of mass density.The corresponding physical interpretations of the cosmological solutions are also discussed.展开更多
Einstein field equations with the cosmological constant is considered in the presence of bulk viscosity in a Bianchi type-I universe.Solutions of the field equations are obtained by assuming the following conditions:t...Einstein field equations with the cosmological constant is considered in the presence of bulk viscosity in a Bianchi type-I universe.Solutions of the field equations are obtained by assuming the following conditions:the bulk viscosity is proportional to the expansion scalarξ∝θ;the expansion scalar is proportional to shear scalarθ∝σ;andΛis proportional to the Hubble parameterΛ∝H.The corresponding interpretations of the cosmological solutions are also discussed.展开更多
文摘We consider a locally rotationally symmetric(LRS)Bianchi type-Ⅱspacetime with a perfect fluid and a variable cosmological constant∧.To solve the Einstein field equations we consider the cosmological term∧to be proportional to R^(-m) with R being the scale factor and m a constant[Phys.Rev.D 58(1998)043506].In this model we obtain∧~H^(2),∧~(R)/R and Larnbda~t^(-2),in agreement with the main dynamical laws for the decay of∧.The physical significance of the cosmological model is also discussed.
文摘Einstein field equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for a Bianchi type-I universe by assuming that the cosmological term is proportional to the Hubble parameter..The variation law for vacuum density was recently proposed by Schützhold on the basis of quantum field estimation in a curved expanding background.The cosmological term tends asymptotically to a genuine cosmological constant and the model tends to a de Sitter universe.We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of a cosmological term.
文摘We study the non existence of shear in locally rotationally symmetric Bianchi type-Ⅲstring cosmological models with bulk viscosity and variable cosmological termΛ.Exact solutions of the field equations are obtained by assuming the conditions:the bulk viscosity is proportional to the expansion scalar,ξ∝θ,expansion scalar is proportional to shear scalar,θ∝σ,and A is proportional to the Hubble parameter.The coefficient of bulk viscosity is assumed to be a power function of mass density.The corresponding physical interpretations of the cosmological solutions are also discussed.
文摘Einstein field equations with the cosmological constant is considered in the presence of bulk viscosity in a Bianchi type-I universe.Solutions of the field equations are obtained by assuming the following conditions:the bulk viscosity is proportional to the expansion scalarξ∝θ;the expansion scalar is proportional to shear scalarθ∝σ;andΛis proportional to the Hubble parameterΛ∝H.The corresponding interpretations of the cosmological solutions are also discussed.
