Epoch dependent dark energy

We present a model in which the parameter w approaches −1 near a particular value of z, and has significant negative values in a restricted range of z. For example, one can have w≈−1 near z = 1, and w>−0.2 from z = 0 to z = 0.3, and for z>9. The ingredients of the model are neutral fermions (which may be neutrinos, neutralinos, etc) which are very weakly coupled to a light scalar field. This model emphasises the importance of the proposed studies of the properties of dark energy into the region z>1.