NONLINEAR EQUATION OF STATE, COSMIC ACCELERATION AND DECELERATION DURING PHANTOM DOMINANCE

In this paper, the RS-II model of brane gravity is considered for the phantom universe using a nonlinear equation of state. Phantom fluid is known to violate the weak energy condition. It is found that this characteristic of phantom energy is affected drastically by the negative brane tension lambda of the RS-II model. It is interesting to see that up to a certain value of energy density rho satisfying rho/lambda < 1, the weak energy condition is violated and the universe superaccelerates. But, as rho increases more, only the strong energy condition is violated and the universe accelerates. When 1 < rho/lambda < 2, even the strong energy condition is not violated and the universe decelerates. Expansion of the universe stops when rho = 2 lambda. This is contrary to earlier results of the phantom universe exhibiting acceleration only.