Cosmological dynamics in sixth-order gravity

We consider the cosmological dynamics in a generalized modified theory of gravity with an R□R term added to the action of the form R + RN. The influence of the R□R term on the known solutions of modified gravity is described. We show that in the particular case of N = 3 the two non-Einsteinian terms are equally important in power-law solutions. These solutions and their stability have been studied using the dynamical system approach. Some results for the case of N ≠ 3 (including stability of the de Sitter solution in the theory under investigation) have been obtained using other methods. © 2011 Pleiades Publishing, Ltd.