Stable cosmological solutions in degenerate theory of gravity
  We study cosmological applications of extended vector-tensor theories, whose
Lagrangians contain up to two derivatives with respect to metric and vector
field. We derive background equations under the assumption of homogeneous and
isotropic universe and study the nature of cosmological perturbations on top of
the background. We found an example of healthy cosmological solutions in
non-trivial degenerate theory of gravity for the first time, where those
perturbations do not suffer from any instabilities, that is, ghost and gradient
instabilities.
