Cosmological solutions of a chiral self-gravitating model of $f(R,(\nabla R)^2,\square R)$ gravity

Abstract: We study modified $f(R,(\nabla R)^2,\square R)$ gravity and show in detail how it can be reduced to Einstein gravity with a few scalar fields and then represented in the form of chiral self-gravitating model of the special type. In further investigation of the model we focus on cosmology and looking for solutions of the dynamic equations of chiral fields and the Einstein-Friedman equations in the Friedman-Robertson-Walker spacetime. Exact solutions of the considered model for zero and constant potential are found. Between them power law solution corresponded to equation of state for stiff matter, de Sitter solution, trigonometric and hyperbolic expansion solution. Various type of chiral fields evolution support listed above solutions.