Modified gravity as an alternative for ACDM cosmology

A reconstruction scheme is developed for modified f (R) gravity with realistic matter ( dark matter, baryons, radiation). Two versions of such theory are constructed: the first one describes the sequence of radiation and matter domination, deceleration-acceleration transition and acceleration era, and the second one is reconstructed from exact Lambda CDM cosmology. The inclusion of a radiation dominated era in the cosmological sequence is qualitatively a new result. The asymptotic behaviour of the first model at late times coincides with the theory containing positive and negative powers of curvature while the second model approaches general relativity without a singularity at zero curvature.