The Λ2 limit of massive gravity

Abstract

Lorentz-invariant massive gravity is usually associated with a strong coupling scale Λ3. By including non-trivial effects from the St¨uckelberg modes, we show that about these vacua, one can push the strong coupling scale to higher values and evade the linear vDVZ-discontinuity. For generic parameters of the theory and generic vacua for the St¨uckelberg fields, the Λ2-decoupling limit of the theory is well-behaved and free of any ghost or gradient-like instabilities. We also discuss the implications for nonlinear sigma models with Lorentzian target spaces.