Complete Decoupling Limit of Ghost-free Massive Gravity
  We present the complete form of the decoupling limit of ghost-free massive
gravity with a Minkowski reference metric, including the full interactions of
the helicity-1 and helicity-0 modes of the massive spin-2 field. While in the
metric language the square root structure of the mass terms makes it difficult
to find a simple way to write down the interactions, we show that using the
vierbein formulation of massive gravity, including Stueckelberg fields for both
diffeomorphism and local Lorentz symmetries, we can find an explicitly resummed
expression for the helicity-1 field interactions. We clarify the equations of
motion for the Lorentz Stueckelberg fields and how these generate the symmetric
vierbein condition which guarantees equivalence between the vierbein and metric
formulations of massive gravity.
