Dark energy from modified F(R)-scalar-Gauss-Bonnet gravity

The modified F(R)-scalar-Gauss-Bonnet gravity is proposed as dark energy model. The reconstruction program for such theory is developed. It is explicitly demonstrated that the known classical universe expansion history (deceleration epoch, transition to acceleration and effective quintessence, phantom or cosmological constant era) may naturally occur in such unified theory for some (reconstructed) classes of scalar potentials. Gauss-Bonnet assisted dark energy is also proposed. The possibility of cosmic acceleration is studied there.Comment: LaTeX, 8 pages, no figure, refs. added, version to appear in Physics Letters