A unique linear theory describing a free massive spin-2 representation
of the Poincare group – Fierz-Pauli model – has
proven to be extremely hard to generalize at the nonlinear level, without
violating its consistency. Recently, a class of four-dimensional,
ghost-free non-linear extensions of
the FP theory has been constructed, which are
natural candidates for describing massive gravity. After
reviewing some formal aspects of this class of theories (and their immediate
extensions) based on the analogy with massive Yang Mills, I will discuss their
relevance for cosmology.
