Early Dark Energy at High Redshifts: Status and Perspectives

TL;DR

This paper updates constraints on early dark energy using various cosmological observations, showing that future measurements could significantly improve our ability to distinguish early dark energy models from the standard $\\Lambda$CDM model.

Contribution

The paper provides the latest observational bounds on early dark energy density at high redshifts and discusses how future data can better differentiate these models from standard cosmology.

Findings

Current upper limit on dark energy density at last scattering: < 2.3×10^{-2} (95% C.L.)

Including high-redshift probes tightens the limit to < 1.4×10^{-3} (95% C.L.)

Future measurements could improve constraints by a factor of ten and distinguish models with high confidence.

Abstract

Early dark energy models, for which the contribution to the dark energy density at high redshifts is not negligible, influence the growth of cosmic structures and could leave observable signatures that are different from the standard cosmological constant cold dark matter ($\Lambda$CDM) model. In this paper, we present updated constraints on early dark energy using geometrical and dynamical probes. From WMAP five-year data, baryon acoustic oscillations and type Ia supernovae luminosity distances, we obtain an upper limit of the dark energy density at the last scattering surface (lss), $\Omega_{\rm EDE}(z_{\rm lss})<2.3\times10^{-2}$ (95% C.L.). When we include higher redshift observational probes, such as measurements of the linear growth factors, Gamma-Ray Bursts (GRBs) and Lyman-$\alpha$ forest (\lya), this limit improves significantly and becomes $\Omega_{\rm EDE}(z_{\rm lss})<1.4\times10^{-3}$ (95% C.L.). Furthermore, we find that future measurements, based on the Alcock-Paczy\'nski test using the 21cm neutral hydrogen line, on GRBs and on the \lya forest, could constrain the behavior of the dark energy component and distinguish at a high confidence level between early dark energy models and pure $\Lambda$CDM. In this case, the constraints on the amount of early dark energy at the last scattering surface improve by a factor ten, when compared to present constraints. We also discuss the impact on the parameter $\gamma$, the growth rate index, which describes the growth of structures in standard and in modified gravity models.