Cosmological models with fluid matter undergoing velocity diffusion
  A new type of fluid matter model in general relativity is introduced, in
which the fluid particles are subject to velocity diffusion without friction.
In order to compensate for the energy gained by the fluid particles due to
diffusion, a cosmological scalar field term is added to the left hand side of
the Einstein equations. This hypothesis promotes diffusion to a new mechanism
for accelerated expansion in cosmology. It is shown that diffusion alters not
only quantitatively, but also qualitatively the global dynamical properties of
the standard cosmological models.
