Model Independent Early Expansion History and Dark Energy

TL;DR

This paper develops a model-independent framework using principal component analysis to constrain the early universe's expansion history and dark energy properties from CMB data, enabling precise limits on early dark energy and relativistic species.

Contribution

It introduces a novel, model-independent method to analyze CMB data for constraining early universe expansion and dark energy, distinguishing between different models in eigenspace.

Findings

CMB data can map expansion history from redshift 0 to 10^5 with subpercent accuracy.

The method can differentiate between models like scaling, dark radiation, and barotropic aether.

Constraints on early dark energy and relativistic species are achievable with upcoming CMB observations.

Abstract

We examine model independent constraints on the high redshift and prerecombination expansion history from cosmic microwave background observations, using a combination of principal component analysis and other techniques. This can be translated to model independent limits on early dark energy and the number of relativistic species $N_{\rm eff}$. Models such as scaling (Doran-Robbers), dark radiation ($\Delta N_{\rm eff}$), and barotropic aether fall into distinct regions of eigenspace and can be easily distinguished from each other. Incoming CMB data will map the expansion history from $z=0$--$10^5$, achieving subpercent precision around recombination, and enable determination of the amount of early dark energy and valuable guidance to its nature.