Interacting phantom energy and avoidance of the big rip singularity

Abstract

Models of the universe with additional (non-gravitational) interaction between the components of the cosmic fluid—the phantom energy and the background—are investigated. A general form of the interaction that is inspired by scalar–tensor theories of gravity is considered. No specific model for the phantom fluid is assumed. We concentrate our investigation on solutions which are free of the coincidence problem. Solutions with constant and dynamical equation-of-state parameters are studied separately. In the last case the model allows for smooth transition from dust in the past into phantom in the future. We found a wide region in the parameter space where the solutions are also free of big rip singularity. Physical arguments, together with arguments based on the analysis of the observational evidence, suggest that phantom models without the big rip singularity might be preferred by nature.