Brane Quintessence

We propose a new quintessence scenario in the brane cosmology, assuming that a quintessence field $Q$ is confined in our 3-dimensional brane world. With a potential $V(Q)= \mu^{\alpha+4} Q^{-\alpha}~(\alpha\geq 2)$, we find that the density parameter of the scalar field decreases as $\Omega_Q \sim a^{-4(\alpha-2)/(\alpha+2)}$ in the epoch of quadratic energy density dominance, if $\alpha\leq 6$. This attractor solution is followed by the usual tracking quintessence scenario after a conventional Friedmann universe is recovered. With an equipartition of initial energy density, we find a natural and successful quintessence model for $\alpha\gsim 4$.