We know dark energy with value of state parameter less than (-1) is called phantom dark energy model. In this model if we assume dark energy to be fluid with value of state parameter=-2, we can say energy density of such dark matter increases with time. My question is whether the above statement violates the concept of accelerating universe. Because the energy density as well as matter density turns out to be negative (i.e. energy density=-AT^-2 ; A=constant) and if we use these values in the acceleration equation,we see the acceleration of the universe (second derivative of the scale factor) is negative.