On the dark sector interactions

It is possible that there exist some interactions between dark energy (DE) and dark matter (DM), and a suitable interaction can alleviate the coincidence problem. Several phenomenological interacting forms are proposed and are fitted with observations in the literature. In this paper we investigate the possible interaction in a way independent of specific interacting forms by the use of observational data (supernovae, BAO, CMB, and Hubble parameter). We divide the whole range of redshift into a few bins and set the interacting term δ(z) to be a constant in each redshift bin. We consider four parametrizations of the equation of state wde for DE and find that δ(z) is likely to cross the noninteracting (δ=0) and have an oscillation form. It suggests that to study the interaction between DE and DM, more general phenomenological forms of the interacting term should be considered.