Cascading Gravity is Ghost Free

TL;DR

This work probes the ghost issue in the 6D cascading gravity model by performing a full perturbative analysis around a flat background with brane tension. It shows that a sufficiently large codimension-2 tension renders the problematic scalar mode healthy, with the kinetic term acquiring a tension-dependent positive contribution and the dangerous mass term canceled by bulk effects. The main result provides a precise bound, $λ_{min}=(2/3) M_4^2 m_6^2$, and demonstrates perturbative ghost-freedom beyond the previously studied decoupling limit, strengthening cascaded gravity as a consistent infrared modification of gravity. Non-linear stability and extensions to higher codimensions remain open directions for future work, but the framework offers a robust basis for exploring IR gravity phenomenology.

Abstract

We perform a full perturbative stability analysis of the 6D cascading gravity model in the presence of 3-brane tension. We demonstrate that for sufficiently large tension on the (flat) 3-brane, there are no ghosts at the perturbative level, consistent with results that had previously only been obtained in a specific 5D decoupling limit. These results establish the cascading gravity framework as a consistent infrared modification of gravity.