Dark Before Light: Testing the Cosmic Expansion History through the Cosmic Microwave Background

TL;DR

This paper examines the possibility of early universe acceleration periods and finds that cosmic microwave background observations strongly restrict such deviations from the standard expansion history.

Contribution

It provides a robust analysis showing that no additional accelerated expansion occurred between Big Bang nucleosynthesis and recombination.

Findings

Accelerated expansion between 1  z  10^5 is excluded by CMB data.

Standard cosmic expansion history is highly robust.

Observations constrain early universe acceleration to very specific epochs.

Abstract

The cosmic expansion history proceeds in broad terms from a radiation dominated epoch to matter domination to an accelerated, dark energy dominated epoch. We investigate whether intermittent periods of acceleration are possible in the early universe -- between Big Bang nucleosynthesis (BBN) and recombination and beyond. We establish that the standard picture is remarkably robust: observations of anisotropies in the cosmic microwave background exclude any extra period of accelerated expansion between 1 \leq z \lesssim 10^5 (corresponding to 5\times10^{-4}\ {\rm eV} \leq T \lesssim 25\ {\rm eV}).