Finite scale factor and future singularities

The main characteristic of the dark energy is its negative pressure. In a homogeneous and isotropic FRW background, we consider several models for the dark energy fluid, which lead to finite time future singularities of the type I-IV, by introducing the pressure density as a function of the scale factor. This approach gives acceptable behavior of the dark energy equation of state. We give various numerical examples of models with type I-IV singularities, that show very similar late time behavior, making it difficult to determine the type of singularity that would take place in the future.
Comment: 24 pages, 3 figures