Cascading DGP

TL;DR

This work generalizes the DGP framework to higher codimensions by cascading localized gravity terms across a 6D bulk with embedded 5D and 4D branes. The construction yields a regular 4D propagator and a gravity cascade from 6D to 4D across distance scales, addressing divergences inherent to codimension-2 setups. A ghost arises from scalar-mode mixing, but introducing a positive tension on the 3-brane generates a healthy localized kinetic term that can remove the ghost within a parameter window where $m_6 < m_5$. The model offers a route to ghost-free, multi-scale gravity with potential cosmological implications, while leaving questions about nonlinear behavior and observational Tensor structure for future work.

Abstract

We present a higher codimension generalization of the DGP scenario which, unlike previous attempts, is free of ghost instabilities. The 4D propagator is made regular by embedding our visible 3-brane within a 4-brane, each with their own induced gravity terms, in a flat 6D bulk. The model is ghost-free if the tension on the 3-brane is larger than a certain critical value, while the induced metric remains flat. The gravitational force law `cascades' from a 6D behavior at the largest distances followed by a 5D and finally a 4D regime at the shortest scales.