Magnetized Viscous Fluid Anisotropic Models in String Cosmology

摘要

We study the evolution of a homogeneous and anisotropic Bianchi type VI_(0) 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 cosmology. 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.