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.