A singularity problem for interacting massive vectors
  Interacting massive spin-1 fields have been widely used in cosmology and
particle physics. We obtain a new condition on the validity of the classical
limit of these theories related to the non-trivial constraints that exist for
vector field components. A violation of this consistency condition causes a
singularity in the time derivative of the auxiliary component and could impact,
for example, the field's cosmic history and superradiance around black holes.
Such a condition is expected to exist generically in many other non-trivially
constrained systems.
