Exact Solution to the "Auxiliary Extra Dimension" Model of Massive Gravity

Understand

The "Auxiliary Extra Dimension" model was proposed in order to provide a geometrical interpretation to modifications of general relativity, in particular to non-linear massive gravity.

• In this context, the theory was shown to be ghost free to third order in perturbations, in the decoupling limit.
• In this work, we exactly solve the equation of motion in the extra dimension, to obtain a purely 4-dimensional theory.
• Using this solution, it is shown that the ghost appears at the fourth order and beyond.