Dark energy in the dark ages

Abstract

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 < ∼ 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 σ8, and the shape and evolution of the nonlinear mass power spectrum for z < 2 (using the LinderWhite 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.

Snapping supernovae at z>1.7

“…On a coarse level the answer is immediately no; we know that structure formed in the universe, in a manner not too different from a universe dominated by matter at z > 2, so dark energy cannot be dynamically important at high redshift (see [62] for details about growth of structure constraints). However, it is worthwhile to address this question quantitatively, from the distance perspective, to show that even percent level distance measurements are insufficient.…”

CMB lensing constraints on neutrinos and dark energy

“…In ΛCDM, the fractional contribution of dark energy density is of order 10 −9 at last scattering. However, many models exist where this can be at the percent level [43], with important impacts on the sound horizon scale and baryon acoustic oscillations, structure formation, and secondary anisotropies [18,19,43,44,45,46,47]. Such early dark energy models follow from physics where the dark energy traces the energy density of the dominant component of the universe, as in high energy physics and string theory models with dilatation symmetries [48].…”

Contiguous redshift parameterizations of the growth index

“…Thus using our redshift dependent parameterizations for the growth index gives an improvement to the fit of the growth rate function of about a factor 150. We also plot γ(z) for various dark energy equations of state, including some early dark energy models (see for example [35,37,38,40] for a discussion of the latter and our appendix for a parameterization). In Table I we list the best fit parameter values of γ 0 and γ a for the various models used.…”