Bianchi-I cosmologies with magnetic and spinor fields

We consider Bianchi type I cosmologies with unidirectional magnetic and electric fields as well as a global spinor field ψ(t) containing a nonlinearity in the form sn, where s = ψ̄ψ and n = const (the special case n = 1 corresponds to a Dirac massive field). The structure of the stress-energy tensor of the spinor field is shown to be the same as that of a perfect fluid with the equation of state p = wρ with the parameter w = n - 1. The Dirac massive spinor field and nonlinear fields with n < 4/3 are shown to be able to provide late-time isotropization. © 2009 Pleiades Publishing, Ltd.