Dodging the dark matter degeneracy while determining the dynamics of
  dark energy
  One of the key issues in cosmology is to establish the nature of dark energy,
and to determine whether the equation of state evolves with time. When
estimating this from distance measurements there is a degeneracy with the
matter density. We show that there exists a simple function of the dark energy
equation of state and its first derivative which is independent of this
degeneracy at all redshifts, and so is a much more robust determinant of the
evolution of dark energy than just its derivative. We show that this function
can be well determined at low redshift from supernovae using Gaussian
Processes, and that this method is far superior to a variety of
parameterisations which are also subject to priors on the matter density. This
shows that parametrised models give very biased constraints on the evolution of
dark energy.
