Calculating the Hubble diagram by perturbation theory
  The effect of density fluctuations upon light propagation is calculated
perturbatively in a matter dominated irrotational universe. The starting point
is the perturbed metric (second order in the perturbation strength), while the
output is the Hubble diagram. Density fluctuations cause this diagram to
broaden to a strip. Moreover, the shift of the diagram mimics accelerated
expansion.
