# Spinor field in Bianchi type-$IX$ space-time

## TL;DR

This paper investigates the influence of spinor fields on Bianchi type-IX universe models, revealing that non-diagonal energy-momentum components restrict the geometry, resulting in either isotropic or locally rotationally symmetric space-times with distinct expansion behaviors.

## Contribution

It demonstrates how spinor fields affect Bianchi type-IX cosmologies, especially regarding energy-momentum tensor components and resulting geometric restrictions, including oscillatory and rapid expansion modes.

## Key findings

- Non-diagonal energy-momentum tensor components impose geometric restrictions.
- Positive bb
gives oscillatory expansion mode.
- Trivial bb
leads to rapid early expansion.

## Abstract

Within the scope of Bianchi type-$IX$ we have studied the role of spinor field in the evolution of the Universe. It is found that unlike the diagonal Bianchi models in this case the components of energy-momentum tensor of spinor field along the principal axis are not the same, 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. As a result the space-time turns out to be either locally rotationally symmetric or isotropic. In this paper we considered the Bianchi type-$IX$ space-time both for a trivial $b$, that corresponds to standard $BIX$ and the one with a non-trivial $b$. It was found that a positive $\lambda_1$ gives rise to an oscillatory mode of expansion, while a trivial $\lambda_1$ leads to rapid expansion at the early stage of evolution.