Dark energy in the dark ages

Non-negligible dark energy density at high redshifts would indicate dark energy physics distinct from a cosmological constant or reasonable canonical scalar fields. Such dark energy can be constrained tightly through investigation of the growth of structure, with limits of less than or similar to 2% of total energy density at z >> 1 for many models. Intermediate dark energy can have effects distinct from its energy density; the dark ages acceleration can be constrained to last less than 5% of a Hubble e-fold time, exacerbating the coincidence problem. Both the total linear growth, or equivalently sigma(8), and the shape and evolution of the nonlinear mass power spectrum for z < 2 (using the Linder-White nonlinear mapping prescription) provide important windows. Probes of growth, such as weak gravitational lensing, can interact with supernovae and CMB distance measurements to scan dark energy behavior over the entire range z = 0-1100. Published by Elsevier B.V.