Scale-dependence in $\Lambda$CDM parameters inferred from the CMB: a possible sign of Early Dark Energy

TL;DR

This paper investigates how the parameters inferred from the CMB power spectrum vary with scale under the EDE model, suggesting scale-dependent shifts could indicate the presence of Early Dark Energy.

Contribution

It demonstrates that if EDE is correct, $ m extit{ extbf{ extbf{Lambda}}}$CDM parameters inferred from different scales should vary, providing a new observational signature for EDE.

Findings

Parameter shifts become significant with smaller scales in mock CMB-S4 data.

Inclusion of smaller scales leads to lower $H_0$, $n_s$, $ m extbf{ extomega}_b$ and higher $ m extbf{ extomega}_m$, $A_s e^{-2 au}$.

These shifts could introduce new tensions with other cosmological measurements.

Abstract

The early dark energy (EDE) model is one of the promising solutions to the Hubble tension. One of the successes of the EDE model is that it can provide a similar fit to the $\Lambda$CDM model for the CMB power spectrum. In this work, I analyze the phenomenology of the EDE and $\Lambda$CDM parameters on the CMB temperature power spectrum and notice that this cannot hold on all scales. Thus, if the real cosmology is as described by the EDE model, the $\Lambda$CDM parameters will be scale-dependent when fitting the CMB power spectrum with the $\Lambda$CDM model, which can be hints for the EDE model. I examine CMB-S4-like observations through mock data analysis and find that parameter shifts are notable. As observations include smaller scales, I find lower $H_0$, $n_s$, $\omega_b$ and higher $\omega_m$, $A_s e^{-2\tau}$, which will also constitute new tensions with other observations. They can serve as a possible signal for the EDE model.