Ghost Condensation in the Brane-World

Motivated by the ghost condensate model, we study the Randall-Sundrum (RS) brane-world with an arbitrary function of the higher derivative kinetic terms, P(X), where X = −(∂φ)2. The five-dimensional Einstein equations reduce to two equations of motion with a constraint between P(X) and the five-dimensional cosmological constant on the brane. For a static extra dimension, P(X) has solutions of the negative kinetic scalar (so called ghost) as well as the ordinary scalar field while the higher derivative terms of X do not appear. On the other hand, it is shown that the small perturbations along the extra dimensional radius (non-static extra dimension) can give rise to the ghost condensation, which presents a possible way to produce a radiation-dominated universe and the vanishing cosmological constant at late times. Finally, we show that the higher derivative effects of ghosts can be responsible for either ghost condensation or cosmic acceleration, depending upon the form of P(X) near its minimum. PACS numbers: 98.80.Cq, 04.50.+h, 11.25.Mj