Can Phantom-Dominated Universe Decelerate Also in Future ?

Abstract

Here Randall-Sundrum brane-gravity models of the homogeneous and flat universe, dominated by phantom fluid, is considered. It is noted that brane-gravity corrections effect the behaviour of phantom fluid in RS-II model (where brane-tension $\lambda$ is negative) drastically. It is interesting to see that, phantom fluid violates the weak energy condition (WEC) till energy density $\rho < \lambda$, but when phantom energy density $\rho$ grows more, the effective equation of state does not violate WEC. Moreover, with increasing phantom energy density, a stage comes when even strong energy condition is not violated due to effect of these corrections. Also expansion stops, when $\rho = 2 \lambda$. As a consequence, RS-II phantom universe accelerates upto a finite time explaining the present cosmic acceleration, but it decelerates later.Thus, RS-II phantom universe is singularity-free. In the case of RS-I model, where $\lambda$ is positive, characteristics of phantom fluid is not suppressed by brane-corrections and phantom universe accelerates ending up in big-rip singularity in finite future time.