Self-accelerating Massive Gravity: Superluminality, Cauchy Surfaces and Strong Coupling

Understand

Self-accelerating solutions in massive gravity provide explicit, calculable examples that exhibit the general interplay between superluminality, the well-posedness of the Cauchy problem, and strong coupling.

• For three particular classes of vacuum solutions, one of which is new to this work, we construct the conformal diagram for the characteristic surfaces on which isotropic stress-energy perturbations propagate.
• With one exception, all solutions necessarily possess spacelike characteristics, indicating perturbative superluminality.
• Foliating the spacetime with these surfaces gives a pathological frame where kinetic terms of the perturbations vanish, confusing the Hamiltonian counting of degrees of freedom.