  In R^2-inflation scalaron slow roll is responsible for the inflationary
stage, while its oscillations reheat the Universe. We find that the same
scalaron decays induced by gravity can also provide the dark matter production
and leptogenesis. With R^2-term and three Majorana fermions added to the
Standard Model, we arrive at the phenomenologically complete theory capable of
simultaneously explaining neutrino oscillations, inflation, reheating, dark
matter and baryon asymmetry of the Universe. Besides the seesaw mechanism in
neutrino sector, we use only gravity, which solves all the problems by
exploiting scalaron.
