Dynamical dark energy or simply cosmic curvature?

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.