Chiral Cosmological Models: Dark Sector Fields Description
  The present review is devoted to a Chiral Cosmological Model as the self-gravitating nonlinear sigma model with the potential of (self)interactions employed in cosmology. The chiral cosmological model has successive applications in descriptions of the inflationary epoch of the Universe evolution; the present accelerated expansion of the Universe also can be described by the chiral fields multiplet as the dark energy in wide sense.   To be more illustrative we are often addressed to the two-component chiral cosmological model. Namely, the two-component chiral cosmological model describing the phantom field with interaction to a canonical scalar field is analyzed in details. New generalized model of quintom character is proposed and exact solutions are founded out.   In the review we represented the perturbation theory for chiral cosmological model with the aim to describe the structure formation using the progress achieved in the inflation theory. It was shown that cosmological perturbations from chiral fields can be decomposed for inflaton and the dark sector perturbations. The two-component model is investigated in details, the general solution for shortwave approximation is obtained and analyzed for power law Universe expansion.   New issue for understanding the features of Universe evolution is proposed by consideration of the dark sector fields on the inflaton background. The results are illustrated for the solutions in the long-wave approximation. 
S.V. Chervon
gr-qc