Field equations in the presence of perfect fluid distribution are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke[1] with the aid of Bianchi type-II, VIII & IX metrics. Exact prefect ...Field equations in the presence of perfect fluid distribution are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke[1] with the aid of Bianchi type-II, VIII & IX metrics. Exact prefect fluid Bianchi type- IX cosmological model is presented since other models doesn’t exist in Brans-Dicke scalar tensor theory of gravitation. Some physical properties of the model are also discussed.展开更多
The locally rotationally symmetric(LRS)Bianchi type-II inflationary cosmological model is investigated for massless scalar field with flat potential and time varyingΛ.To obtain the deterministic solution,it is assume...The locally rotationally symmetric(LRS)Bianchi type-II inflationary cosmological model is investigated for massless scalar field with flat potential and time varyingΛ.To obtain the deterministic solution,it is assumed that scale factor is a(t)~e^(Ht) as we considered previously for Bianchi type-I spacetime andΛ~a^(-2) as considered by Chen and Wu,where H is the Hubble constant and effective potential V(φ)=const;φHigg's field.It is shown that such a time varyingΛleads to no conflict with existing observations.However,it does change the predictions of standard cosmology in the matter-dominated phase and alleviates some problems in reconciling observations with the inflationary scenario.The model represents anisotropic spacetime in general.However,the model isotropizes for large values of t andβ=3H^(2),whereβis constant.The physical and geometrical aspects of the model in the context of an inflationary scenario is also discussed.展开更多
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
The locally rotationally symmetric Bianchi type-II magnetized string cosmological model with bulk viscous fluid is investigated.The magnetic field is due to an electric current produced along the x−axis.Thus the magne...The locally rotationally symmetric Bianchi type-II magnetized string cosmological model with bulk viscous fluid is investigated.The magnetic field is due to an electric current produced along the x−axis.Thus the magnetic field is in the y–z plane and F23 is the only non−vanishing component of electromagnetic field tensor Fij.To obtain the deterministic model in terms of cosmic time t,we have assumed the conditionξθ=const,whereξis the coefficient of bulk viscosity andθis the expansion in the model.展开更多
We study the evolution of the equation of state of viscous dark energy in the scope of Bianchi type III space-time. We consider a case where the dark energy is minimally coupled to the perfect fluid, as well as in dir...We study the evolution of the equation of state of viscous dark energy in the scope of Bianchi type III space-time. We consider a case where the dark energy is minimally coupled to the perfect fluid, as well as in direct interaction with it. The viscosity and the interaction between the two fluids are parameterized by constants 40 and σ, respectively. We have made a detailed investigation of the cosmological implications of this parametrization. To differentiate between different dark energy models, we have performed a geometrical diagnostic by using the statefinder pair {s, r}.展开更多
We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-int...We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-interacting and interacting cases and then we examine its future by applying a hyperbolic scale factor. It is shown that in the non-interacting case, depending on the value of the anisotropy parameter K, the DE EoS parameter varies from phantom to quintessence whereas in the interacting case the EoS parameter varies in the quintessence region. However, in both cases, the DE EoS parameter ωde ultimately （i.e. at z ： -1） tends to the cosmological constant （ωde = -1）. Moreover, we fix the cosmological bound on the anisotropy parameter K by using recent observational data about the Hubble parameter.展开更多
文摘Field equations in the presence of perfect fluid distribution are obtained in a scalar tensor theory of gravitation proposed by Brans and Dicke[1] with the aid of Bianchi type-II, VIII & IX metrics. Exact prefect fluid Bianchi type- IX cosmological model is presented since other models doesn’t exist in Brans-Dicke scalar tensor theory of gravitation. Some physical properties of the model are also discussed.
文摘The locally rotationally symmetric(LRS)Bianchi type-II inflationary cosmological model is investigated for massless scalar field with flat potential and time varyingΛ.To obtain the deterministic solution,it is assumed that scale factor is a(t)~e^(Ht) as we considered previously for Bianchi type-I spacetime andΛ~a^(-2) as considered by Chen and Wu,where H is the Hubble constant and effective potential V(φ)=const;φHigg's field.It is shown that such a time varyingΛleads to no conflict with existing observations.However,it does change the predictions of standard cosmology in the matter-dominated phase and alleviates some problems in reconciling observations with the inflationary scenario.The model represents anisotropic spacetime in general.However,the model isotropizes for large values of t andβ=3H^(2),whereβis constant.The physical and geometrical aspects of the model in the context of an inflationary scenario is also discussed.
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The locally rotationally symmetric Bianchi type-II magnetized string cosmological model with bulk viscous fluid is investigated.The magnetic field is due to an electric current produced along the x−axis.Thus the magnetic field is in the y–z plane and F23 is the only non−vanishing component of electromagnetic field tensor Fij.To obtain the deterministic model in terms of cosmic time t,we have assumed the conditionξθ=const,whereξis the coefficient of bulk viscosity andθis the expansion in the model.
文摘We study the evolution of the equation of state of viscous dark energy in the scope of Bianchi type III space-time. We consider a case where the dark energy is minimally coupled to the perfect fluid, as well as in direct interaction with it. The viscosity and the interaction between the two fluids are parameterized by constants 40 and σ, respectively. We have made a detailed investigation of the cosmological implications of this parametrization. To differentiate between different dark energy models, we have performed a geometrical diagnostic by using the statefinder pair {s, r}.
基金a research fund from the Mahshahr Branch of Islamic Azad University under the project entitled "Interacting Viscous Dark Energy And Cold Dark Matter In An Anisotropic Universe"
文摘We study the interaction between dark energy （DE） and dark matter in the scope of anisotropic Bianchi type-I space-time. First we derive the general form of the DE equation of state （EoS） parameter in both non-interacting and interacting cases and then we examine its future by applying a hyperbolic scale factor. It is shown that in the non-interacting case, depending on the value of the anisotropy parameter K, the DE EoS parameter varies from phantom to quintessence whereas in the interacting case the EoS parameter varies in the quintessence region. However, in both cases, the DE EoS parameter ωde ultimately （i.e. at z ： -1） tends to the cosmological constant （ωde = -1）. Moreover, we fix the cosmological bound on the anisotropy parameter K by using recent observational data about the Hubble parameter.
