Can we distinguish early dark energy from a cosmological constant?

TL;DR

This paper investigates whether early dark energy can be distinguished from a cosmological constant by analyzing its effects on cosmic structure and the power spectrum, using simulations and observational data.

Contribution

It provides a detailed comparison of EDE and ΛCDM models, highlighting the potential of large-scale power spectrum measurements to differentiate them.

Findings

Large-scale power spectrum differences up to 15% between EDE and ΛCDM.

Most large-scale structure statistics are similar in EDE and ΛCDM.

Current observations favor no EDE, but extreme models show measurable differences.

Abstract

Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology using recent measurements of the cosmic microwave background and baryon acoustic oscillations. The best-fitting models favour no EDE; here we consider extreme examples which are in mild tension with current observations in order to explore the observational consequences of a maximally allowed amount of EDE. We study the non-linear evolution of cosmic structure in EDE cosmologies using large volume N-body simulations. Many large-scale structure statistics are found to be very similar between the $\Lambda$ cold dark matter ($\Lambda$CDM) and EDE models. We find that the most promising way to distinguish EDE from $\Lambda$CDM is to measure the power spectrum on large scales, where differences of up to 15% are expected.