Investigating early dark energy with new observations

Abstract

This paper mainly presents updated constraints on several types of early dark energy (EDE) models proposed by V. Pettorino et al. using observations of cosmic microwave background radiation (CMB) from Planck satellite, the Pantheon Type Ia supernovae (SNIa) sample, and baryon acoustic oscillation (BAO) measurements. The results yield stringent upper limits on the constant EDE fraction parameter ${\Omega }_e$. While the present equation of state (EoS) of dark energy $w_0$ in the EDE1 model suggests a mild tendency towards a value less than $-1$, these models remain compatible with the $\Lambda$CDM scenario. Partly as a result of this slight tendency towards phantom late-time physics, EDE1 model supports a higher Hubble constant value, potentially narrowing the Hubble tension gap. The global fitting results also align with the notion that the constraint ability on ${\Omega }_e$ weakens when dark energy is present only over a limited period after last scattering. Furthermore, by using the formalism of Fisher information matrix, we forecast uncertainties in the measured parameters of EDE models from the next-generation “Stage 4” CMB (CMB-S4) experiment. Forecasted precision of $w_0$ and ${\Omega }_e$ surpasses certain prior works, and most other basic parameters exhibit significantly higher limit precision compared to Planck 2018 results within the $\Lambda$CDM framework. To confirm the presence of EDE within the EDE1$\sim$EDE4 parameterization frameworks, further advancements in observations are crucial.