SUPER-ACCELERATED EXPANSION AND ASYMPTOTIC SOLUTIONS IN SCALAR-TENSOR COSMOLOGY

We consider FLRW cosmological models with barotropic fluid in the framework of scalar-tensor theories of gravity (STG) with arbitrary coupling function and potential, set in the Jordan frame. These models can exhibit (super-)accelerated expansion without a need to introduce any unusual matter component, and we give a necessary condition on the coupling function of the scalar field which must be satisfied to allow (super-)acceleration to occur. To satisfy also the Solar System observations the models have to be close to the limit of general relativity (GR), which has been shown to function as an attractor in a large class of STG theories. Approximating the cosmological equations near this limit we find the phase trajectories for the potential dominated case, and determine a condition when the flow of all trajectories is attracted to the GR point.