Self-consistent solutions to the nonlinear spinor field equations in general relativity are studied for the case of Bianchi type-I (BI) space-time. It is shown that, for some special type of nonlinearity the model provides a regular solution, but this singularity-free solution is attained at the cost of breaking the dominant energy condition in the Hawking-Penrose theorem. It is also shown that the introduction of a $\Lambda$ term in the Lagrangian generates oscillations of the BI model, which is not the case in the absence of a $\Lambda$ term. Moreover, for the linear spinor field, the $\Lambda$ term provides oscillatory solutions, which are regular everywhere, without violating the dominant energy condition.

We consider a self-consistent system of interacting spinor and scalar fields within the framework of a Bianchi type-I (BI) cosmological model filled with perfect fluid. The interacting term in the Lagrangian is chosen in the form of derivative coupling, i.e., ${\mathcal{L}}_{\mathrm{int}}=(\lambda /2){\phi }_{,\alpha }{\phi }^{,\alpha }F.\mathrm{}$ Here F is a power or trigonometric function of the invariants I and/or J constructed from bilinear spinor forms $S=\overline{\psi }\psi$ and $P=i\overline{\psi }{\gamma }^5\psi .$ Self-consistent solutions to the spinor, scalar, and BI gravitational field equations are obtained. The problems of an initial singularity and the asymptotically isotropization process of the initially anisotropic space-time are studied. The role of the cosmological constant $(\Lambda$ term) in the evolution of a BI Universe is studied. It is shown that a positive $\Lambda$ generates an oscillatory mode of expansion of the BI model, whereas if F in ${\mathcal{L}}_{\mathrm{int}}$ is chosen to be a trigonometric function of its arguments, there exists a nonexponential mode of evolution even with a negative $\Lambda .$ It is shown also that for a suitable choice of problem parameters the present model allows regular solutions without a broken dominant energy condition.

A self-consistent system of interacting nonlinear spinor and scalar fields within the scope of a Bianchi type-I cosmological model filled with perfect fluid is considered. Exact self-consistent solutions to the corresponding field equations are obtained. A role of the spinor field in the evolution of the Universe is studied. It is shown that the spinor field gives rise to an accelerated mode of expansion of the Universe. Early in the evolution, the spinor field nonlinearity generates an accelerated mode of expansion. The rapid growth of the Universe in this case results in the earlier isotropization. At the later evolution the acceleration of the Universe is provided with a spinor mass.