w d =?1 in interacting quintessence model

A model consisting of a quintessence scalar field interacting with cold dark matter is considered. The conditions required to reach w _d =?1 are discussed. It is shown that, depending on the potential considered for the quintessence, crossing the phantom divide line puts some constraints on the interaction between dark energy and dark matter. This also may determine the ratio of dark matter to dark energy density at w _d =?1.