Abstract
We show that the assumption of a flat universe induces critically large errors in
reconstructing the dark energy equation of state at 
even if the true cosmic curvature is very small, 
or less. The spuriously reconstructed
w(z)
shows a range of unusual behaviour, including crossing of the phantom divide
and mimicking of standard tracking quintessence models. For 1% curvature and
ΛCDM, the error
in w grows
rapidly above z∼0.9
reaching (50%,100%) by
redshifts of (2.5,2.9)
respectively, due to the long cosmological lever arm. Interestingly, the
w(z)
reconstructed from distance data and Hubble rate measurements have opposite
trends due to the asymmetric influence of the curved geodesics. These results show
that including curvature as a free parameter is imperative in any future analyses
attempting to pin down the dynamics of dark energy, especially at moderate or high
redshifts.