Ghost Condensation in the Brane-World

TL;DR

This paper explores ghost condensation phenomena in a brane-world model with higher derivative kinetic terms, showing how radion perturbations can induce ghost condensation, leading to a radiation-dominated universe and potential late-time acceleration.

Contribution

It demonstrates that radion perturbations in a generalized brane-world setup can trigger ghost condensation, offering insights into cosmic acceleration mechanisms.

Findings

Radion perturbations can induce ghost condensation.

The model predicts a radiation-dominated universe at late times.

Inclusion of bulk matter stabilizes the radion and explains cosmic acceleration.

Abstract

Motivated by the ghost condensate model, we study the Randall-Sundrum (RS) brane-world with an arbitrary function of the higher derivative kinetic terms, $\mathcal{P}(X)$, where $X=-(\nabla \phi)^{2}$. The five-dimensional Einstein equations reduce to two equations of motion with a constraint between $\mathcal{P}(X)$ and the five-dimensional cosmological constant on the brane. For a static extra dimension, $\mathcal{P}(X)$ has solutions for both a negative kinetic scalar (so called {\textit{ghost}}) as well as an ordinary scalar field. However ghost condensation cannot take place. We show that small perturbations along the extra dimensional radius (the radion) can give rise to ghost condensation. This produces a radiation-dominated universe and the vanishing cosmological constant at late times but destabilizes the radion. This instability can be resolved by an inclusion of bulk matter along $y$-direction, which finally presents a possible explanation of the late-time cosmic acceleration.