Self-gravitating darkon fluid with anisotropic scaling
  The fluid model for the dark sector of the universe (darkon fluid) introduced
previously in \cite{PRD} is reformulated as a modified model involving only
variables from physical phase space. The Lagrangian of the model does not
possess a free particle limit and hence the particles it describes, darkons,
exist only as a self-gravitating fluid. This darkon fluid presents a dynamical
realisation of the zero-mass Galilean algebra extended by anisotropic
dilational symmetry with dynamical exponent $z=5/3$. The model possesses
cosmologically relevant solutions which are identical to those of \cite{PRD}.
We derive also the equations for the cosmological perturbations at early times
and determine their solutions. In addition, we discuss also some implications
of adding higher spatial-derivative terms.
