Cosmology of Extended Proca-Nuevo
  Proca-Nuevo is a non-linear theory of a massive spin-1 field which enjoys a
non-linearly realized constraint that distinguishes it among other generalized
vector models. We show that the theory may be extended by the addition of
operators of the Generalized Proca class without spoiling the primary
constraint that is necessary for consistency, allowing to interpolate between
Generalized Proca operators and Proca-Nuevo ones. The constraint is maintained
on flat spacetime and on any fixed curved background. Upon mixing extended
Proca-Nuevo dynamically with gravity, we show that the constraint gets broken
in a Planck scale suppressed way. We further prove that the theory may be
covariantized in models that allow for consistent and ghost-free cosmological
solutions. We study the models in the presence of perfect fluid matter, and
show that they describe the correct number of dynamical variables and derive
their dispersion relations and stability criteria. We also exhibit, in a
specific set-up, explicit hot Big Bang solutions featuring a late-time
self-accelerating epoch, and which are such that all the stability and
subluminality conditions are satisfied and where gravitational waves behave
precisely as in General Relativity.
