Higher Curvature Brane Corrections to the DGP Model

TL;DR

This paper studies how adding higher curvature terms to the DGP brane model significantly alters its spectrum, introducing massive ghost excitations that cause instabilities but may help address the cosmological constant problem.

Contribution

It demonstrates that higher curvature brane corrections induce massive ghost modes in the DGP model, impacting its stability and cosmological implications.

Findings

Massive ghost excitations with Planck-scale mass are generated.

These ghosts cause an instability of Minkowski vacuum on a Hubble time scale.

At large distances, tachyonic excitations decouple from matter.

Abstract

We investigate the Dvali-Gabadadze-Porrati (DGP) model corrected by higher curvature brane terms. We show that these corrections have a dramatic impact on the spectrum of the model at the linearized level. Owing to the presence of higher derivatives in the field equations very massive ghost excitations with mass of order of Planck mass are generated in the ordinary branch of the model. These excitations describe an instability of Minkowski vacuum with time-scale of order of the Hubble time. At large distances these tachyonic excitations are expected to decouple from brane-localized matter. Our modified DGP model represents therefore a very promising framework for solving of the cosmological constant problem, in which Planck-scale physics is responsible for the elementary excitations driving the accelerated expansion of the universe, but the time-scale of the instability is settled by gravitational physics at large scales.