On theoretical models of dark energy

In this talk I divide dark energy models (precisely speaking, models to explain origin of current cosmic acceleration) existing in literatures in to three classes. The first one is to ascribe the cosmic acceleration to modifications of general relativity at cosmological scales. The second one is due to the backreaction of perturbations, or say, the effect of inhomogeneity of the universe. The third one is some exotic component in the universe, which appears in the right hand side of Einstein's equations. For each class I demonstrate some examples. (authors)