The dark side of curvature

Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance dA(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ωk in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and dA(z) up to sufficiently high redshifts z ∼ 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z) − Ωk degeneracy.