Effective dark matter fluid with higher derivative corrections
  The effective field theory for hydrodynamics allows to write the action
functional for fluid. In this paper, some simplest possible higher derivative
terms in the fluid action and the cosmological consequences of their presence
are considered. Particular attention is given to dark matter, modelled as a
dust with higher derivative corrections. We study the conditions of absence of
singularities in the solutions of the background and perturbed equations and
investigate the evolution of perturbations in two simple models of matter
dominated Universe. There is a range of parameters describing the higher
derivative terms, in which the short-wavelength perturbations of dark matter
are suppressed and the dark matter can be seen as fairly homogeneous on a
sufficiently small scale.
