Non-linear Equation of State, COSMIC Acceleration and Deceleration During Phantom-Dominance

Abstract

Here, RS-II model of brane-gravity is considerd for phantom universe using non-linear equation of stste. Phantom fluid is known to violate the weak energy condition. In this paper, 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 upto a certain value of energy density $\rho$ satisfying $\rho/\lambda < 1$, weak energy condition is violated and universe super-accelerates. But as $\rho$ increases more, only strong energy condition is violated and universe accelerates. When $1 < \rho/\lambda <2$, even strong energy condition is not violated and universe decelerates. Expansion of the universe stops, when $\rho = 2 \lambda$. This is contrary to earlier results of phantom universe exhibiting acceleration only.