Ghosts in the self-accelerating DGP branch with Gauss–Bonnet effect

Yen-Wei Liu,Mariam Bouhmadi-López,Keisuke Izumi,Pisin Chen

doi:10.1140/epjc/s10052-015-3463-0

Abstract

The Dvali-Gabadadze-Porrati brane-world model provides a possible approach to address the late-time cosmic acceleration. However, it has subsequently been pointed out that a ghost instability will arise on the self-accelerating branch. Here, we carefully investigate whether this ghost problem could be possibly cured by introducing the Gauss-Bonnet term in the five-dimensional bulk action, a natural generalization to the Dvali-Gabadadze-Porrati model. Our analysis is carried out for a background where a de Sitter brane is embedded in an anti-de Sitter bulk. Our result shows that the ghost excitations cannot be avoided even in this modified model.

Highlights

In recent years, the late-time cosmic acceleration has been confirmed by several observational pieces of evidence [1,2,3,4,5,6]
We looked into a generalized DGP brane-world scenario with a GB term as well as a cosmological constant both incorporated in the bulk action
To check whether this framework can possibly provide a way out of the DGP ghost instability, we have studied the linear perturbations around a de Sitter self-accelerating brane embedded in an AdS5 bulk space-time

Summary

Introduction

The late-time cosmic acceleration has been confirmed by several observational pieces of evidence [1,2,3,4,5,6]. In the original DGP model, the ghost conditions have been carefully checked [15,16,17,18,19,20], and one of the above mentioned condition is always satisfied, i.e. one of the ghost modes appears This means that the flip of the sign in the kinetic term of the brane-bending mode happens when the squared value of the mass of the lightest KK graviton is 2H 2. We study the linear perturbations around the background given by (2.8) and (2.9) with = +1 which includes as a particular case the self-accelerating branch, and carefully examine whether or not the ghost excitations appearing in the DGP model could be possibly evaded in this framework.

The model

Perturbed equations

Effective action and existence of ghosts

Summary