Testing the Copernican principle by constraining spatial homogeneity
  We present a new programme for placing constraints on radial inhomogeneity in
a dark-energy dominated universe. We introduce a new measure to quantify
violations of the Copernican principle. Any violation of this principle would
interfere with our interpretation of any dark-energy evolution. In particular,
we find that current observations place reasonably tight constraints on
possible late-time violations of the Copernican principle: the allowed area in
the parameter space of amplitude and scale of a spherical inhomogeneity around
the observer has to be reduced by a factor of three so as to confirm the
Copernican principle. Then, by marginalizing over possible radial inhomogeneity
we provide the first constraints on the cosmological constant which are free of
the homogeneity prior prevalent in cosmology.
