Accelerated expansion from a modified-quadratic gravity

We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard Einstein-Hilbert action R is replaced by f(phi)R+f(R) where f(phi)=phi (2) and f(R)=AR (2)+BR (mu nu) R (mu nu),(A,B)aa"e. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form it was shown that the universe is dominated by dark energy with equation of state parameter wa parts per thousand a'0.2 and is accelerated in time with a scale factor evolving like a(t)aet (5/3) and B+3Aa parts per thousand 0.036. When, B+3A -> a which corresponds for the purely quadratic theory, the scale factor evolves like a(t)aet (1/2) whereas when B+3A -> 0 which corresponds for the purely scalar tensor theory we found when a(t)aet (1.98). In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter vary respectively like. It was shown that for some special values of chi, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the model is independent of the quadratic gravity corrections. Additional consequences are discussed.