Brane quintessence

We propose a new quintessence scenario in brane cosmology, assuming that a quintessence field Q is confined in our three-dimensional brane world. With a potential V(Q) = μ^α+4Q-^α (α≥2), we find that the density parameter of the scalar field decreases as Ω_Q∼a^{-4(α-2)/(α+2)} in the epoch of quadratic energy density dominance, if α≤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 α≳4.