A Proof Of Ghost Freedom In de Rham-Gabadadze-Tolley Massive Gravity
  We identify different helicity degrees of freedom of Fierz-Paulian massive
gravity around generic backgrounds. We show that the two-parameter family
proposed by de Rham, Gabadadze, and Tolley always propagates five degrees of
freedom and therefore is free from the Boulware-Deser ghost. The analysis has a
number of byproducts, among which (a) it shows how the original decoupling
limit construction ensures ghost freedom of the full theory, (b) it reveals an
enhanced symmetry of the theory around linearized backgrounds, and (c) it
allows us to give an algorithm for finding dispersion relations. The proof
naturally extends to generalizations of the theory with a reference metric
different from Minkowski.
