Infrared-modified Universe
  We consider a Hubble expansion law modified in the infra-red by
distance-dependent terms, and attempt to enforce homogeneity upon it. As a
warm-up, we re-derive the basic kinematics of a Friedman Robertson Walker
universe without using standard general relativistic tools: we describe the
expansion with a `Hubble velocity field' rather than with a four dimensional
metric. Then we extend this analysis to the modified Hubble expansion and
impose a transformation for velocities that makes it identical for all comoving
observers, and therefore homogeneous. We derive the modified equation for light
ray trajectories and other geometrical properties that are incompatible with
the general relativistic description. We speculate that this extended framework
could help addressing cosmological problems which are normally explained with
accelerating expansions.
