  It is proved that in order to obtain a model of the accelerated cosmic
expansion the thing one only need to do is to add a perturbation term to the
Einstein-Hilbert Lagrangian. This term leads to some symmetry breaking terms in
the fields equation, which makes the cosmic expansion accelerating. A vacuum de
Sitter solution is obtained. A new explanation of the acceleration of the
cosmic expansion is presented. In this model the changing of the expansion from
decelerating to accelerating is an intrinsic property of the universe without
need of an exotic dark energy. The acceleration of the cosmic expansion is
induced by the symmetry breaking perturbation of the gravitational energy. The
cosmological constant problem, the coincidence problem and the problem of
phantom divide line crossing are naturally solved. The results of the model are
roughly consistent with the observations.
