Brane Induced Gravity, its Ghost and the Cosmological Constant Problem

Understand

"Brane Induced Gravity" is regarded as a promising framework for addressing the cosmological constant problem, but it also suffers from a ghost instability for parameter values that make it phenomenologically viable.

• We carry out a detailed analysis of codimension > 2 models employing gauge invariant variables in a flat background approximation.
• It is argued that using instead a curved background sourced by the brane would not resolve the ghost issue, unless a very specific condition is satisfied (if satisfiable at all).
• As for other properties of the model, from an explicit analysis of the 4-dimensional graviton propagator we extract a mass, a decay width and a momentum dependent modification of the gravitational coupling for the spin 2 mode.