An Introduction to Cascading Gravity and Degravitation

TL;DR

The paper frames degravitation as an IR modification of gravity achieved by promoting the graviton mass to a nonlocal operator, constraining the parameter \alpha to realize a high-pass filter. It first analyzes the DGP model as a baseline with \alpha=1/2 and then constructs a higher-codimension cascading gravity setup to realize an explicit nonlinear degravitation, addressing divergences and ghost issues via brane tension and finite brane thickness. The results show a GR regime at short scales and a dimensional cascade at larger scales, offering a concrete mechanism to suppress the cosmological constant's gravitational backreaction. While promising, the approach relies on strong coupling and careful regularization, underscoring the need for a UV-complete framework.

Abstract

Cascading gravity is an explicit realization of the idea of degravitation, where gravity behaves as a high-pass filter. This could explain why a large cosmological constant does not backreact as much as anticipated from standard General Relativity. The model relies on the presence of at least two infinite extra dimensions while our world is confined on a four-dimensional brane. Gravity is then four-dimensional at short distances and becomes weaker and weaker at larger distances.