Cosmic anti-friction and accelerated expansion

We explain an accelerated expansion of the present universe, suggested from observations of supernovae of type Ia at high redshift, by introducing an anti-frictional force that is self-consistently exerted on the particles of the cosmic substratum. Cosmic anti-friction, which is intimately related to ``particle production'', is shown to give rise to an effective negative pressure of the cosmic medium. While other explanations for an accelerated expansion (cosmological constant, quintessence) introduce a component of dark energy besides ``standard'' cold dark matter (CDM) we resort to a phenomenological one-component model of CDM with internal self-interactions. We demonstrate how the dynamics of the LambdaCDM model may be recovered as a special case of cosmic anti-friction. We discuss the connection with two-component models and obtain an attractor behavior for the ratio of the energy densities of both components which provides a possible phenomenological solution to the coincidence problem.