Cosmological string model in the presence of a magnetic field: spinor approach and quantum loop effects

A Bianchi type-I string cosmological model in the presence of a magnetic field is investigated. A nonlinear spinor field simulation of the massive cosmic strings is presented. In the spinor approach the model is nonsingular at the end of the evolution and does not allow the anisotropic Universe to turn into an isotropic one. Quantum effects of a cosmic string are examined in the framework of loop quantum cosmology. In the first part of the paper we investigated an anisotropic spacetime of BI type describing a string cosmology model. Using a nonlinear spinor field simulation, we studied the singularities, asymptotic behaviors, isotropization during the evolution of the Universe. In the second part we considered the quantum effects. Loop quantum cosmology offers a different picture of the evolution of the spacetime, free of singularities. In spite of its simplicity, BI models are suitable for investigation of the evolution of the Universe, dark matter, spacetime singularities, etc. The extension of the effective loop quantum cosmology approach to anisotropic models is very promising, deserving further studies. (authors)