New Constraints on the Early Expansion History

TL;DR

This paper uses recent CMB data from Planck and WMAP9 to constrain the early universe's expansion rate and constituents like dark energy and relativistic particles in a model-independent way, achieving high precision.

Contribution

It provides the first model-independent constraints on the early universe's expansion history from redshift z=10^5 using high-resolution CMB data.

Findings

Limits on early dark energy to 2-16% (95% CL)

Constraints on extra relativistic degrees of freedom to 0.71 neutrino species

Early dark energy constraints within specific models are 1.2-3.3%

Abstract

Cosmic microwave background measurements have pushed to higher resolution, lower noise, and more sky coverage. These data enable a unique test of the early universe's expansion rate and constituents such as effective number of relativistic degrees of freedom and dark energy. Using the most recent data from Planck and WMAP9, we constrain the expansion history in a model independent manner from today back to redshift z=10^5. The Hubble parameter is mapped to a few percent precision, limiting early dark energy and extra relativistic degrees of freedom within a model independent approach to 2-16% and 0.71 equivalent neutrino species respectively (95% CL). Within dark radiation, barotropic aether, and Doran-Robbers models, the early dark energy constraints are 3.3%, 1.9%, 1.2% respectively.