| Abstract: | Oscillations of the F(R) dark energy around the phantom divide line, ω
DE=−1, both during the matter era and also in the de Sitter epoch are investigated. The analysis during the de Sitter epoch
is revisited by expanding the modified equations of motion around the de Sitter solution. Then, during the matter epoch, the
time dependence of the dark energy perturbations is discussed by using two different local expansions. For high values of
the red shift, the matter epoch is a stable point of the theory, giving the possibility to expand the F(R)-functions in terms of the dark energy perturbations. In the late-time matter era, the realistic case is considered where
dark energy tends to a constant. The results obtained are confirmed by precise numerical computation on a specific model of
exponential gravity. A novel and very detailed discussion is provided on the critical points in the matter era and on the
relation of the oscillations with possible singularities. |
