Spinor field in Bianchi type-$II$ Universe

Abstract

Within the scope of Bianchi type-$II$ cosmological model we have studied the role of spinor field in the evolution of the Universe. It is found that in this case the components of energy-momentum tensor of spinor field along the principal axis are different, i.e. $T_1^1 \ne T_2^2 \ne T_3^3$, even in absence of spinor field nonlinearity. The presence of nontrivial non-diagonal components of energy-momentum tensor of the spinor field imposes severe restrictions both on geometry of space-time and on the spinor field itself. Depending on the choice of $f(x_3)$ the space-time might be either locally rotationally symmetric or isotropic. In this paper we considered the Bianchi type-$II$ space-time both for a trivial and nontrivial $b$. It was found that while a positive $\lambda_1$ in case of $f^\prime \ne 0$ gives rise to oscillatory mode of evolution, in case of $f^\prime = 0$ it leads to accelerated mode of expansion.