Recent observations of SN Ia suggest that the universe has entered a stage of an accelerated expansion.
Given this, a dark energy component with negative pressure was suggested to account for the invisible fuel that drives the current accelerated expansion.
However, in the LCDM model there exists a theoretical problem of cosmic coincidence: why is the vacuum density comparable with the critical density at the present epoch in the long history of the universe?
Cosmological models with a coupling between dark energy and dark matter could provide a phenomenological explanation to the cosmic coincidence problem.
We place observational constraints on a coupling between dark energy and dark matter by using SNLS data, CMB shift parameter and BAO.
Our results indicate that the uncoupled LCDM model still remains a good fit to the data, but the negative coupling with a phantom equation of state of dark energy is slightly favored over the LCDM model.