Infrared-modified gravities and massive gravitons
  We review some theoretical and phenomenological aspects of massive gravities in 4 dimensions. We start from the Fierz--Pauli theory with Lorentz-invariant mass terms and then proceed to Lorentz-violating masses. Unlike the former theory, some models with Lorentz-violation have no pathologies in the spectrum in flat and nearly flat backgrounds and lead to interesting phenomenology. 
V. A. Rubakov (1), P. G. Tinyakov (1 and 2) ((1) INR, Moscow, (2) ULB,   Brussels)