Abstract
We study the evolution of a homogeneous and anisotropic Bianchi type VI0 cosmological model in the presence of magnetic field and viscous fluid together with a cloud of cosmic strings in general relativity. Since Viscous fluid and magnetic field have cosmological origin, it is interesting to discuss the effects of viscous fluid and magnetic field on the expansion history of the universe in early and later stages of evolution in string cosmol- ogy. Exact solutions of the field equations are obtained using the equation of state for a cloud of strings. The bulk viscous coefficient is assumed to be inversely proportional to the expansion scalar. The two string models, namely, geometrical(Nambu string) and Takabayasi (p-string) string models are discussed with magnetized and non-magnetized viscous fluid by taking certain physical conditions. We also examine numerically the effects of bulk viscosity and magnetic field on potential in each string model. We find that magnetic field and viscous fluid play important role during the early evolution of the universe. We observe that the viscous term affects the evolution much rapid as compare to magnetic field. The presence of viscous term prevents the universe to be empty. The other physical and geometrical aspects of each string model are also discussed in detail.
Highlights
In recent years cosmic strings have been studied to describe the early evolution of the universe
The strings dominate and the tension along the string is equal to its energy density per unit length as we call it string dust model
We have studied anisotropic Bianchi VI0 string cosmological model with viscous fluid and magnetic field in general relativity by taking certain physical assumptions
Summary
In recent years cosmic strings have been studied to describe the early evolution of the universe. The presently observed universe is almost isotropic at large as we have discussed above, the isotropization problem appears inevitably in any study of anisotropic cosmologies The presence of such a field demands the use of a class of space -times more general than the Friedmann - Roberstion-Walker ones, since the isotropy is broken. It would be worthwhile to discuss the early and late phases of the universe in BVI0 magnetized bulk viscous string cosmological model in general relativity. The paper is organized as follows: In Section 2 we present spatially homogeneous and anisotropic BVI0 space time and derive the field equations for cosmic string with magnetic field and viscous fluid.
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